Initial vendor packages

Signed-off-by: Valentin Popov <valentin@popov.link>

1 files changed, 1197 insertions, 0 deletions

diff --git a/vendor/exr/src/meta/header.rs b/vendor/exr/src/meta/header.rs
new file mode 100644
index 0000000..b322b18
--- /dev/null
+++ b/vendor/exr/src/meta/header.rs
@@ -0,0 +1,1197 @@
+
+//! Contains collections of common attributes.
+//! Defines some data types that list all standard attributes.
+
+use std::collections::HashMap;
+use crate::meta::attribute::*; // FIXME shouldn't this need some more imports????
+use crate::meta::*;
+use crate::math::Vec2;
+
+// TODO rename header to LayerDescription!
+
+/// Describes a single layer in a file.
+/// A file can have any number of layers.
+/// The meta data contains one header per layer.
+#[derive(Clone, Debug, PartialEq)]
+pub struct Header {
+
+    /// List of channels in this layer.
+    pub channels: ChannelList,
+
+    /// How the pixel data of all channels in this layer is compressed. May be `Compression::Uncompressed`.
+    pub compression: Compression,
+
+    /// Describes how the pixels of this layer are divided into smaller blocks.
+    /// A single block can be loaded without processing all bytes of a file.
+    ///
+    /// Also describes whether a file contains multiple resolution levels: mip maps or rip maps.
+    /// This allows loading not the full resolution, but the smallest sensible resolution.
+    //
+    // Required if file contains deep data or multiple layers.
+    // Note: This value must agree with the version field's tile bit and deep data bit.
+    // In this crate, this attribute will always have a value, for simplicity.
+    pub blocks: BlockDescription,
+
+    /// In what order the tiles of this header occur in the file.
+    pub line_order: LineOrder,
+
+    /// The resolution of this layer. Equivalent to the size of the `DataWindow`.
+    pub layer_size: Vec2<usize>,
+
+    /// Whether this layer contains deep data.
+    pub deep: bool,
+
+    /// This library supports only deep data version 1.
+    pub deep_data_version: Option<i32>,
+
+    /// Number of chunks, that is, scan line blocks or tiles, that this image has been divided into.
+    /// This number is calculated once at the beginning
+    /// of the read process or when creating a header object.
+    ///
+    /// This value includes all chunks of all resolution levels.
+    ///
+    ///
+    /// __Warning__
+    /// _This value is relied upon. You should probably use `Header::with_encoding`,
+    /// which automatically updates the chunk count._
+    pub chunk_count: usize,
+
+    // Required for deep data (deepscanline and deeptile) layers.
+    // Note: Since the value of "maxSamplesPerPixel"
+    // maybe be unknown at the time of opening the
+    // file, the value “ -1 ” is written to the file to
+    // indicate an unknown value. When the file is
+    // closed, this will be overwritten with the correct value.
+    // If file writing does not complete
+    // correctly due to an error, the value -1 will
+    // remain. In this case, the value must be derived
+    // by decoding each chunk in the layer
+    /// Maximum number of samples in a single pixel in a deep image.
+    pub max_samples_per_pixel: Option<usize>,
+
+    /// Includes mandatory fields like pixel aspect or display window
+    /// which must be the same for all layers.
+    pub shared_attributes: ImageAttributes,
+
+    /// Does not include the attributes required for reading the file contents.
+    /// Excludes standard fields that must be the same for all headers.
+    pub own_attributes: LayerAttributes,
+}
+
+/// Includes mandatory fields like pixel aspect or display window
+/// which must be the same for all layers.
+/// For more attributes, see struct `LayerAttributes`.
+#[derive(Clone, PartialEq, Debug)]
+pub struct ImageAttributes {
+
+    /// The rectangle anywhere in the global infinite 2D space
+    /// that clips all contents of the file.
+    pub display_window: IntegerBounds,
+
+    /// Aspect ratio of each pixel in this header.
+    pub pixel_aspect: f32,
+
+    /// The chromaticities attribute of the image. See the `Chromaticities` type.
+    pub chromaticities: Option<Chromaticities>,
+
+    /// The time code of the image.
+    pub time_code: Option<TimeCode>,
+
+    /// Contains custom attributes.
+    /// Does not contain the attributes already present in the `ImageAttributes`.
+    /// Contains only attributes that are standardized to be the same for all headers: chromaticities and time codes.
+    pub other: HashMap<Text, AttributeValue>,
+}
+
+/// Does not include the attributes required for reading the file contents.
+/// Excludes standard fields that must be the same for all headers.
+/// For more attributes, see struct `ImageAttributes`.
+#[derive(Clone, PartialEq)]
+pub struct LayerAttributes {
+
+    /// The name of this layer.
+    /// Required if this file contains deep data or multiple layers.
+    // As this is an attribute value, it is not restricted in length, may even be empty
+    pub layer_name: Option<Text>,
+
+    /// The top left corner of the rectangle that positions this layer
+    /// within the global infinite 2D space of the whole file.
+    /// This represents the position of the `DataWindow`.
+    pub layer_position: Vec2<i32>,
+
+    /// Part of the perspective projection. Default should be `(0, 0)`.
+    // TODO same for all layers?
+    pub screen_window_center: Vec2<f32>,
+
+    // TODO same for all layers?
+    /// Part of the perspective projection. Default should be `1`.
+    pub screen_window_width: f32,
+
+    /// The white luminance of the colors.
+    /// Defines the luminance in candelas per square meter, Nits, of the rgb value `(1, 1, 1)`.
+    // If the chromaticities and the whiteLuminance of an RGB image are
+    // known, then it is possible to convert the image's pixels from RGB
+    // to CIE XYZ tristimulus values (see function RGBtoXYZ() in header
+    // file ImfChromaticities.h).
+    pub white_luminance: Option<f32>,
+
+    /// The adopted neutral of the colors. Specifies the CIE (x,y) frequency coordinates that should
+    /// be considered neutral during color rendering. Pixels in the image
+    /// whose CIE (x,y) frequency coordinates match the adopted neutral value should
+    /// be mapped to neutral values on the given display.
+    pub adopted_neutral: Option<Vec2<f32>>,
+
+    /// Name of the color transform function that is applied for rendering the image.
+    pub rendering_transform_name: Option<Text>,
+
+    /// Name of the color transform function that computes the look modification of the image.
+    pub look_modification_transform_name: Option<Text>,
+
+    /// The horizontal density, in pixels per inch.
+    /// The image's vertical output density can be computed using `horizontal_density * pixel_aspect_ratio`.
+    pub horizontal_density: Option<f32>,
+
+    /// Name of the owner.
+    pub owner: Option<Text>,
+
+    /// Additional textual information.
+    pub comments: Option<Text>,
+
+    /// The date of image creation, in `YYYY:MM:DD hh:mm:ss` format.
+    // TODO parse!
+    pub capture_date: Option<Text>,
+
+    /// Time offset from UTC.
+    pub utc_offset: Option<f32>,
+
+    /// Geographical image location.
+    pub longitude: Option<f32>,
+
+    /// Geographical image location.
+    pub latitude: Option<f32>,
+
+    /// Geographical image location.
+    pub altitude: Option<f32>,
+
+    /// Camera focus in meters.
+    pub focus: Option<f32>,
+
+    /// Exposure time in seconds.
+    pub exposure: Option<f32>,
+
+    /// Camera aperture measured in f-stops. Equals the focal length
+    /// of the lens divided by the diameter of the iris opening.
+    pub aperture: Option<f32>,
+
+    /// Iso-speed of the camera sensor.
+    pub iso_speed: Option<f32>,
+
+    /// If this is an environment map, specifies how to interpret it.
+    pub environment_map: Option<EnvironmentMap>,
+
+    /// Identifies film manufacturer, film type, film roll and frame position within the roll.
+    pub film_key_code: Option<KeyCode>,
+
+    /// Specifies how texture map images are extrapolated.
+    /// Values can be `black`, `clamp`, `periodic`, or `mirror`.
+    pub wrap_mode_name: Option<Text>,
+
+    /// Frames per second if this is a frame in a sequence.
+    pub frames_per_second: Option<Rational>,
+
+    /// Specifies the view names for multi-view, for example stereo, image files.
+    pub multi_view_names: Option<Vec<Text>>,
+
+    /// The matrix that transforms 3D points from the world to the camera coordinate space.
+    /// Left-handed coordinate system, y up, z forward.
+    pub world_to_camera: Option<Matrix4x4>,
+
+    /// The matrix that transforms 3D points from the world to the "Normalized Device Coordinate" space.
+    /// Left-handed coordinate system, y up, z forward.
+    pub world_to_normalized_device: Option<Matrix4x4>,
+
+    /// Specifies whether the pixels in a deep image are sorted and non-overlapping.
+    pub deep_image_state: Option<Rational>,
+
+    /// If the image was cropped, contains the original data window.
+    pub original_data_window: Option<IntegerBounds>,
+
+    /// An 8-bit rgba image representing the rendered image.
+    pub preview: Option<Preview>,
+
+    /// Name of the view, which is typically either `"right"` or `"left"` for a stereoscopic image.
+    pub view_name: Option<Text>,
+
+    /// The name of the software that produced this image.
+    pub software_name: Option<Text>,
+
+    /// The near clip plane of the virtual camera projection.
+    pub near_clip_plane: Option<f32>,
+
+    /// The far clip plane of the virtual camera projection.
+    pub far_clip_plane: Option<f32>,
+
+    /// The field of view angle, along the horizontal axis, in degrees.
+    pub horizontal_field_of_view: Option<f32>,
+
+    /// The field of view angle, along the horizontal axis, in degrees.
+    pub vertical_field_of_view: Option<f32>,
+
+    /// Contains custom attributes.
+    /// Does not contain the attributes already present in the `Header` or `LayerAttributes` struct.
+    /// Does not contain attributes that are standardized to be the same for all layers: no chromaticities and no time codes.
+    pub other: HashMap<Text, AttributeValue>,
+}
+
+
+impl LayerAttributes {
+
+    /// Create default layer attributes with a data position of zero.
+    pub fn named(layer_name: impl Into<Text>) -> Self {
+        Self {
+            layer_name: Some(layer_name.into()),
+            .. Self::default()
+        }
+    }
+
+    /// Set the data position of this layer.
+    pub fn with_position(self, data_position: Vec2<i32>) -> Self {
+        Self { layer_position: data_position, ..self }
+    }
+
+    /// Set all common camera projection attributes at once.
+    pub fn with_camera_frustum(
+        self,
+        world_to_camera: Matrix4x4,
+        world_to_normalized_device: Matrix4x4,
+        field_of_view: impl Into<Vec2<f32>>,
+        depth_clip_range: std::ops::Range<f32>,
+    ) -> Self
+    {
+        let fov = field_of_view.into();
+
+        Self {
+            world_to_normalized_device: Some(world_to_normalized_device),
+            world_to_camera: Some(world_to_camera),
+            horizontal_field_of_view: Some(fov.x()),
+            vertical_field_of_view: Some(fov.y()),
+            near_clip_plane: Some(depth_clip_range.start),
+            far_clip_plane: Some(depth_clip_range.end),
+            ..self
+        }
+    }
+}
+
+impl ImageAttributes {
+
+    /// Set the display position and size of this image.
+    pub fn new(display_window: IntegerBounds) -> Self {
+        Self {
+            pixel_aspect: 1.0,
+            chromaticities: None,
+            time_code: None,
+            other: Default::default(),
+            display_window,
+        }
+    }
+
+    /// Set the display position to zero and use the specified size for this image.
+    pub fn with_size(size: impl Into<Vec2<usize>>) -> Self {
+        Self::new(IntegerBounds::from_dimensions(size))
+    }
+}
+
+
+
+
+impl Header {
+
+    /// Create a new Header with the specified name, display window and channels.
+    /// Use `Header::with_encoding` and the similar methods to add further properties to the header.
+    ///
+    /// The other settings are left to their default values:
+    /// - RLE compression
+    /// - display window equal to data window
+    /// - tiles (64 x 64 px)
+    /// - unspecified line order
+    /// - no custom attributes
+    pub fn new(name: Text, data_size: impl Into<Vec2<usize>>, channels: SmallVec<[ChannelDescription; 5]>) -> Self {
+        let data_size: Vec2<usize> = data_size.into();
+
+        let compression = Compression::RLE;
+        let blocks = BlockDescription::Tiles(TileDescription {
+            tile_size: Vec2(64, 64),
+            level_mode: LevelMode::Singular,
+            rounding_mode: RoundingMode::Down
+        });
+
+        Self {
+            layer_size: data_size,
+            compression,
+            blocks,
+
+            channels: ChannelList::new(channels),
+            line_order: LineOrder::Unspecified,
+
+            shared_attributes: ImageAttributes::with_size(data_size),
+            own_attributes: LayerAttributes::named(name),
+
+            chunk_count: compute_chunk_count(compression, data_size, blocks),
+
+            deep: false,
+            deep_data_version: None,
+            max_samples_per_pixel: None,
+        }
+    }
+
+    /// Set the display window, that is, the global clipping rectangle.
+    /// __Must be the same for all headers of a file.__
+    pub fn with_display_window(mut self, display_window: IntegerBounds) -> Self {
+        self.shared_attributes.display_window = display_window;
+        self
+    }
+
+    /// Set the offset of this layer.
+    pub fn with_position(mut self, position: Vec2<i32>) -> Self {
+        self.own_attributes.layer_position = position;
+        self
+    }
+
+    /// Set compression, tiling, and line order. Automatically computes chunk count.
+    pub fn with_encoding(self, compression: Compression, blocks: BlockDescription, line_order: LineOrder) -> Self {
+        Self {
+            chunk_count: compute_chunk_count(compression, self.layer_size, blocks),
+            compression, blocks, line_order,
+            .. self
+        }
+    }
+
+    /// Set **all** attributes of the header that are not shared with all other headers in the image.
+    pub fn with_attributes(self, own_attributes: LayerAttributes) -> Self {
+        Self { own_attributes, .. self }
+    }
+
+    /// Set **all** attributes of the header that are shared with all other headers in the image.
+    pub fn with_shared_attributes(self, shared_attributes: ImageAttributes) -> Self {
+        Self { shared_attributes, .. self }
+    }
+
+    /// Iterate over all blocks, in the order specified by the headers line order attribute.
+    /// Unspecified line order is treated as increasing line order.
+    /// Also enumerates the index of each block in the header, as if it were sorted in increasing line order.
+    pub fn enumerate_ordered_blocks(&self) -> impl Iterator<Item=(usize, TileIndices)> + Send {
+        let increasing_y = self.blocks_increasing_y_order().enumerate();
+
+        // TODO without box?
+        let ordered: Box<dyn Send + Iterator<Item=(usize, TileIndices)>> = {
+            if self.line_order == LineOrder::Decreasing { Box::new(increasing_y.rev()) }
+            else { Box::new(increasing_y) }
+        };
+
+        ordered
+    }
+
+    /*/// Iterate over all blocks, in the order specified by the headers line order attribute.
+    /// Also includes an index of the block if it were `LineOrder::Increasing`, starting at zero for this header.
+    pub fn enumerate_ordered_blocks(&self) -> impl Iterator<Item = (usize, TileIndices)> + Send {
+        let increasing_y = self.blocks_increasing_y_order().enumerate();
+
+        let ordered: Box<dyn Send + Iterator<Item = (usize, TileIndices)>> = {
+            if self.line_order == LineOrder::Decreasing {
+                Box::new(increasing_y.rev()) // TODO without box?
+            }
+            else {
+                Box::new(increasing_y)
+            }
+        };
+
+        ordered
+    }*/
+
+    /// Iterate over all tile indices in this header in `LineOrder::Increasing` order.
+    pub fn blocks_increasing_y_order(&self) -> impl Iterator<Item = TileIndices> + ExactSizeIterator + DoubleEndedIterator {
+        fn tiles_of(image_size: Vec2<usize>, tile_size: Vec2<usize>, level_index: Vec2<usize>) -> impl Iterator<Item=TileIndices> {
+            fn divide_and_rest(total_size: usize, block_size: usize) -> impl Iterator<Item=(usize, usize)> {
+                let block_count = compute_block_count(total_size, block_size);
+                (0..block_count).map(move |block_index| (
+                    block_index, calculate_block_size(total_size, block_size, block_index).expect("block size calculation bug")
+                ))
+            }
+
+            divide_and_rest(image_size.height(), tile_size.height()).flat_map(move |(y_index, tile_height)|{
+                divide_and_rest(image_size.width(), tile_size.width()).map(move |(x_index, tile_width)|{
+                    TileIndices {
+                        size: Vec2(tile_width, tile_height),
+                        location: TileCoordinates { tile_index: Vec2(x_index, y_index), level_index, },
+                    }
+                })
+            })
+        }
+
+        let vec: Vec<TileIndices> = {
+            if let BlockDescription::Tiles(tiles) = self.blocks {
+                match tiles.level_mode {
+                    LevelMode::Singular => {
+                        tiles_of(self.layer_size, tiles.tile_size, Vec2(0, 0)).collect()
+                    },
+                    LevelMode::MipMap => {
+                        mip_map_levels(tiles.rounding_mode, self.layer_size)
+                            .flat_map(move |(level_index, level_size)|{
+                                tiles_of(level_size, tiles.tile_size, Vec2(level_index, level_index))
+                            })
+                            .collect()
+                    },
+                    LevelMode::RipMap => {
+                        rip_map_levels(tiles.rounding_mode, self.layer_size)
+                            .flat_map(move |(level_index, level_size)| {
+                                tiles_of(level_size, tiles.tile_size, level_index)
+                            })
+                            .collect()
+                    }
+                }
+            }
+            else {
+                let tiles = Vec2(self.layer_size.0, self.compression.scan_lines_per_block());
+                tiles_of(self.layer_size, tiles, Vec2(0, 0)).collect()
+            }
+        };
+
+        vec.into_iter() // TODO without collect
+    }
+
+    /* TODO
+    /// The block indices of this header, ordered as they would appear in the file.
+    pub fn ordered_block_indices<'s>(&'s self, layer_index: usize) -> impl 's + Iterator<Item=BlockIndex> {
+        self.enumerate_ordered_blocks().map(|(chunk_index, tile)|{
+            let data_indices = self.get_absolute_block_pixel_coordinates(tile.location).expect("tile coordinate bug");
+
+            BlockIndex {
+                layer: layer_index,
+                level: tile.location.level_index,
+                pixel_position: data_indices.position.to_usize("data indices start").expect("data index bug"),
+                pixel_size: data_indices.size,
+            }
+        })
+    }*/
+
+    // TODO reuse this function everywhere
+    /// The default pixel resolution of a single block (tile or scan line block).
+    /// Not all blocks have this size, because they may be cutoff at the end of the image.
+    pub fn max_block_pixel_size(&self) -> Vec2<usize> {
+        match self.blocks {
+            BlockDescription::ScanLines => Vec2(self.layer_size.0, self.compression.scan_lines_per_block()),
+            BlockDescription::Tiles(tiles) => tiles.tile_size,
+        }
+    }
+
+    /// Calculate the position of a block in the global infinite 2D space of a file. May be negative.
+    pub fn get_block_data_window_pixel_coordinates(&self, tile: TileCoordinates) -> Result<IntegerBounds> {
+        let data = self.get_absolute_block_pixel_coordinates(tile)?;
+        Ok(data.with_origin(self.own_attributes.layer_position))
+    }
+
+    /// Calculate the pixel index rectangle inside this header. Is not negative. Starts at `0`.
+    pub fn get_absolute_block_pixel_coordinates(&self, tile: TileCoordinates) -> Result<IntegerBounds> {
+        if let BlockDescription::Tiles(tiles) = self.blocks {
+            let Vec2(data_width, data_height) = self.layer_size;
+
+            let data_width = compute_level_size(tiles.rounding_mode, data_width, tile.level_index.x());
+            let data_height = compute_level_size(tiles.rounding_mode, data_height, tile.level_index.y());
+            let absolute_tile_coordinates = tile.to_data_indices(tiles.tile_size, Vec2(data_width, data_height))?;
+
+            if absolute_tile_coordinates.position.x() as i64 >= data_width as i64 || absolute_tile_coordinates.position.y() as i64 >= data_height as i64 {
+                return Err(Error::invalid("data block tile index"))
+            }
+
+            Ok(absolute_tile_coordinates)
+        }
+        else { // this is a scanline image
+            debug_assert_eq!(tile.tile_index.0, 0, "block index calculation bug");
+
+            let (y, height) = calculate_block_position_and_size(
+                self.layer_size.height(),
+                self.compression.scan_lines_per_block(),
+                tile.tile_index.y()
+            )?;
+
+            Ok(IntegerBounds {
+                position: Vec2(0, usize_to_i32(y)),
+                size: Vec2(self.layer_size.width(), height)
+            })
+        }
+
+        // TODO deep data?
+    }
+
+    /// Return the tile index, converting scan line block coordinates to tile indices.
+    /// Starts at `0` and is not negative.
+    pub fn get_block_data_indices(&self, block: &CompressedBlock) -> Result<TileCoordinates> {
+        Ok(match block {
+            CompressedBlock::Tile(ref tile) => {
+                tile.coordinates
+            },
+
+            CompressedBlock::ScanLine(ref block) => {
+                let size = self.compression.scan_lines_per_block() as i32;
+
+                let diff = block.y_coordinate.checked_sub(self.own_attributes.layer_position.y()).ok_or(Error::invalid("invalid header"))?;
+                let y = diff.checked_div(size).ok_or(Error::invalid("invalid header"))?;
+
+                if y < 0 {
+                    return Err(Error::invalid("scan block y coordinate"));
+                }
+
+                TileCoordinates {
+                    tile_index: Vec2(0, y as usize),
+                    level_index: Vec2(0, 0)
+                }
+            },
+
+            _ => return Err(Error::unsupported("deep data not supported yet"))
+        })
+    }
+
+    /// Computes the absolute tile coordinate data indices, which start at `0`.
+    pub fn get_scan_line_block_tile_coordinates(&self, block_y_coordinate: i32) -> Result<TileCoordinates> {
+        let size = self.compression.scan_lines_per_block() as i32;
+
+        let diff = block_y_coordinate.checked_sub(self.own_attributes.layer_position.1).ok_or(Error::invalid("invalid header"))?;
+        let y = diff.checked_div(size).ok_or(Error::invalid("invalid header"))?;
+
+        if y < 0 {
+            return Err(Error::invalid("scan block y coordinate"));
+        }
+
+        Ok(TileCoordinates {
+            tile_index: Vec2(0, y as usize),
+            level_index: Vec2(0, 0)
+        })
+    }
+
+    /// Maximum byte length of an uncompressed or compressed block, used for validation.
+    pub fn max_block_byte_size(&self) -> usize {
+        self.channels.bytes_per_pixel * match self.blocks {
+            BlockDescription::Tiles(tiles) => tiles.tile_size.area(),
+            BlockDescription::ScanLines => self.compression.scan_lines_per_block() * self.layer_size.width()
+            // TODO What about deep data???
+        }
+    }
+
+    /// Returns the number of bytes that the pixels of this header will require
+    /// when stored without compression. Respects multi-resolution levels and subsampling.
+    pub fn total_pixel_bytes(&self) -> usize {
+        assert!(!self.deep);
+
+        let pixel_count_of_levels = |size: Vec2<usize>| -> usize {
+            match self.blocks {
+                BlockDescription::ScanLines => size.area(),
+                BlockDescription::Tiles(tile_description) => match tile_description.level_mode {
+                    LevelMode::Singular => size.area(),
+
+                    LevelMode::MipMap => mip_map_levels(tile_description.rounding_mode, size)
+                        .map(|(_, size)| size.area()).sum(),
+
+                    LevelMode::RipMap => rip_map_levels(tile_description.rounding_mode, size)
+                        .map(|(_, size)| size.area()).sum(),
+                }
+            }
+        };
+
+        self.channels.list.iter()
+            .map(|channel: &ChannelDescription|
+                pixel_count_of_levels(channel.subsampled_resolution(self.layer_size)) * channel.sample_type.bytes_per_sample()
+            )
+            .sum()
+
+    }
+
+    /// Approximates the maximum number of bytes that the pixels of this header will consume in a file.
+    /// Due to compression, the actual byte size may be smaller.
+    pub fn max_pixel_file_bytes(&self) -> usize {
+        assert!(!self.deep);
+
+        self.chunk_count * 64 // at most 64 bytes overhead for each chunk (header index, tile description, chunk size, and more)
+            + self.total_pixel_bytes()
+    }
+
+    /// Validate this instance.
+    pub fn validate(&self, is_multilayer: bool, long_names: &mut bool, strict: bool) -> UnitResult {
+
+        self.data_window().validate(None)?;
+        self.shared_attributes.display_window.validate(None)?;
+
+        if strict {
+            if is_multilayer {
+                if self.own_attributes.layer_name.is_none() {
+                    return Err(missing_attribute("layer name for multi layer file"));
+                }
+            }
+
+            if self.blocks == BlockDescription::ScanLines && self.line_order == LineOrder::Unspecified {
+                return Err(Error::invalid("unspecified line order in scan line images"));
+            }
+
+            if self.layer_size == Vec2(0, 0) {
+                return Err(Error::invalid("empty data window"));
+            }
+
+            if self.shared_attributes.display_window.size == Vec2(0,0) {
+                return Err(Error::invalid("empty display window"));
+            }
+
+            if !self.shared_attributes.pixel_aspect.is_normal() || self.shared_attributes.pixel_aspect < 1.0e-6 || self.shared_attributes.pixel_aspect > 1.0e6 {
+                return Err(Error::invalid("pixel aspect ratio"));
+            }
+
+            if self.own_attributes.screen_window_width < 0.0 {
+                return Err(Error::invalid("screen window width"));
+            }
+        }
+
+        let allow_subsampling = !self.deep && self.blocks == BlockDescription::ScanLines;
+        self.channels.validate(allow_subsampling, self.data_window(), strict)?;
+
+        for (name, value) in &self.shared_attributes.other {
+            attribute::validate(name, value, long_names, allow_subsampling, self.data_window(), strict)?;
+        }
+
+        for (name, value) in &self.own_attributes.other {
+            attribute::validate(name, value, long_names, allow_subsampling, self.data_window(), strict)?;
+        }
+
+        // this is only to check whether someone tampered with our precious values, to avoid writing an invalid file
+        if self.chunk_count != compute_chunk_count(self.compression, self.layer_size, self.blocks) {
+            return Err(Error::invalid("chunk count attribute")); // TODO this may be an expensive check?
+        }
+
+        // check if attribute names appear twice
+        if strict {
+            for (name, _) in &self.shared_attributes.other {
+                if self.own_attributes.other.contains_key(name) {
+                    return Err(Error::invalid(format!("duplicate attribute name: `{}`", name)));
+                }
+            }
+
+            for &reserved in header::standard_names::ALL.iter() {
+                let name  = Text::from_bytes_unchecked(SmallVec::from_slice(reserved));
+                if self.own_attributes.other.contains_key(&name) || self.shared_attributes.other.contains_key(&name) {
+                    return Err(Error::invalid(format!(
+                        "attribute name `{}` is reserved and cannot be custom",
+                        Text::from_bytes_unchecked(reserved.into())
+                    )));
+                }
+            }
+        }
+
+        if self.deep {
+            if strict {
+                if self.own_attributes.layer_name.is_none() {
+                    return Err(missing_attribute("layer name for deep file"));
+                }
+
+                if self.max_samples_per_pixel.is_none() {
+                    return Err(Error::invalid("missing max samples per pixel attribute for deepdata"));
+                }
+            }
+
+            match self.deep_data_version {
+                Some(1) => {},
+                Some(_) => return Err(Error::unsupported("deep data version")),
+                None => return Err(missing_attribute("deep data version")),
+            }
+
+            if !self.compression.supports_deep_data() {
+                return Err(Error::invalid("compression method does not support deep data"));
+            }
+        }
+
+        Ok(())
+    }
+
+    /// Read the headers without validating them.
+    pub fn read_all(read: &mut PeekRead<impl Read>, version: &Requirements, pedantic: bool) -> Result<Headers> {
+        if !version.is_multilayer() {
+            Ok(smallvec![ Header::read(read, version, pedantic)? ])
+        }
+        else {
+            let mut headers = SmallVec::new();
+
+            while !sequence_end::has_come(read)? {
+                headers.push(Header::read(read, version, pedantic)?);
+            }
+
+            Ok(headers)
+        }
+    }
+
+    /// Without validation, write the headers to the byte stream.
+    pub fn write_all(headers: &[Header], write: &mut impl Write, is_multilayer: bool) -> UnitResult {
+        for header in headers {
+            header.write(write)?;
+        }
+
+        if is_multilayer {
+            sequence_end::write(write)?;
+        }
+
+        Ok(())
+    }
+
+    /// Read the value without validating.
+    pub fn read(read: &mut PeekRead<impl Read>, requirements: &Requirements, pedantic: bool) -> Result<Self> {
+        let max_string_len = if requirements.has_long_names { 256 } else { 32 }; // TODO DRY this information
+
+        // these required attributes will be filled when encountered while parsing
+        let mut tiles = None;
+        let mut block_type = None;
+        let mut version = None;
+        let mut chunk_count = None;
+        let mut max_samples_per_pixel = None;
+        let mut channels = None;
+        let mut compression = None;
+        let mut data_window = None;
+        let mut display_window = None;
+        let mut line_order = None;
+
+        let mut dwa_compression_level = None;
+
+        let mut layer_attributes = LayerAttributes::default();
+        let mut image_attributes = ImageAttributes::new(IntegerBounds::zero());
+
+        // read each attribute in this header
+        while !sequence_end::has_come(read)? {
+            let (attribute_name, value) = attribute::read(read, max_string_len)?;
+
+            // if the attribute value itself is ok, record it
+            match value {
+                Ok(value) => {
+                    use crate::meta::header::standard_names as name;
+                    use crate::meta::attribute::AttributeValue::*;
+
+                    // if the attribute is a required attribute, set the corresponding variable directly.
+                    // otherwise, add the attribute to the vector of custom attributes
+
+                    // the following attributes will only be set if the type matches the commonly used type for that attribute
+                    match (attribute_name.as_slice(), value) {
+                        (name::BLOCK_TYPE, Text(value)) => block_type = Some(attribute::BlockType::parse(value)?),
+                        (name::TILES, TileDescription(value)) => tiles = Some(value),
+                        (name::CHANNELS, ChannelList(value)) => channels = Some(value),
+                        (name::COMPRESSION, Compression(value)) => compression = Some(value),
+                        (name::DATA_WINDOW, IntegerBounds(value)) => data_window = Some(value),
+                        (name::DISPLAY_WINDOW, IntegerBounds(value)) => display_window = Some(value),
+                        (name::LINE_ORDER, LineOrder(value)) => line_order = Some(value),
+                        (name::DEEP_DATA_VERSION, I32(value)) => version = Some(value),
+
+                        (name::MAX_SAMPLES, I32(value)) => max_samples_per_pixel = Some(
+                            i32_to_usize(value, "max sample count")?
+                        ),
+
+                        (name::CHUNKS, I32(value)) => chunk_count = Some(
+                            i32_to_usize(value, "chunk count")?
+                        ),
+
+                        (name::NAME, Text(value)) => layer_attributes.layer_name = Some(value),
+                        (name::WINDOW_CENTER, FloatVec2(value)) => layer_attributes.screen_window_center = value,
+                        (name::WINDOW_WIDTH, F32(value)) => layer_attributes.screen_window_width = value,
+
+                        (name::WHITE_LUMINANCE, F32(value)) => layer_attributes.white_luminance = Some(value),
+                        (name::ADOPTED_NEUTRAL, FloatVec2(value)) => layer_attributes.adopted_neutral = Some(value),
+                        (name::RENDERING_TRANSFORM, Text(value)) => layer_attributes.rendering_transform_name = Some(value),
+                        (name::LOOK_MOD_TRANSFORM, Text(value)) => layer_attributes.look_modification_transform_name = Some(value),
+                        (name::X_DENSITY, F32(value)) => layer_attributes.horizontal_density = Some(value),
+
+                        (name::OWNER, Text(value)) => layer_attributes.owner = Some(value),
+                        (name::COMMENTS, Text(value)) => layer_attributes.comments = Some(value),
+                        (name::CAPTURE_DATE, Text(value)) => layer_attributes.capture_date = Some(value),
+                        (name::UTC_OFFSET, F32(value)) => layer_attributes.utc_offset = Some(value),
+                        (name::LONGITUDE, F32(value)) => layer_attributes.longitude = Some(value),
+                        (name::LATITUDE, F32(value)) => layer_attributes.latitude = Some(value),
+                        (name::ALTITUDE, F32(value)) => layer_attributes.altitude = Some(value),
+                        (name::FOCUS, F32(value)) => layer_attributes.focus = Some(value),
+                        (name::EXPOSURE_TIME, F32(value)) => layer_attributes.exposure = Some(value),
+                        (name::APERTURE, F32(value)) => layer_attributes.aperture = Some(value),
+                        (name::ISO_SPEED, F32(value)) => layer_attributes.iso_speed = Some(value),
+                        (name::ENVIRONMENT_MAP, EnvironmentMap(value)) => layer_attributes.environment_map = Some(value),
+                        (name::KEY_CODE, KeyCode(value)) => layer_attributes.film_key_code = Some(value),
+                        (name::WRAP_MODES, Text(value)) => layer_attributes.wrap_mode_name = Some(value),
+                        (name::FRAMES_PER_SECOND, Rational(value)) => layer_attributes.frames_per_second = Some(value),
+                        (name::MULTI_VIEW, TextVector(value)) => layer_attributes.multi_view_names = Some(value),
+                        (name::WORLD_TO_CAMERA, Matrix4x4(value)) => layer_attributes.world_to_camera = Some(value),
+                        (name::WORLD_TO_NDC, Matrix4x4(value)) => layer_attributes.world_to_normalized_device = Some(value),
+                        (name::DEEP_IMAGE_STATE, Rational(value)) => layer_attributes.deep_image_state = Some(value),
+                        (name::ORIGINAL_DATA_WINDOW, IntegerBounds(value)) => layer_attributes.original_data_window = Some(value),
+                        (name::DWA_COMPRESSION_LEVEL, F32(value)) => dwa_compression_level = Some(value),
+                        (name::PREVIEW, Preview(value)) => layer_attributes.preview = Some(value),
+                        (name::VIEW, Text(value)) => layer_attributes.view_name = Some(value),
+
+                        (name::NEAR, F32(value)) => layer_attributes.near_clip_plane = Some(value),
+                        (name::FAR, F32(value)) => layer_attributes.far_clip_plane = Some(value),
+                        (name::FOV_X, F32(value)) => layer_attributes.horizontal_field_of_view = Some(value),
+                        (name::FOV_Y, F32(value)) => layer_attributes.vertical_field_of_view = Some(value),
+                        (name::SOFTWARE, Text(value)) => layer_attributes.software_name = Some(value),
+
+                        (name::PIXEL_ASPECT, F32(value)) => image_attributes.pixel_aspect = value,
+                        (name::TIME_CODE, TimeCode(value)) => image_attributes.time_code = Some(value),
+                        (name::CHROMATICITIES, Chromaticities(value)) => image_attributes.chromaticities = Some(value),
+
+                        // insert unknown attributes of these types into image attributes,
+                        // as these must be the same for all headers
+                        (_, value @ Chromaticities(_)) |
+                        (_, value @ TimeCode(_)) => {
+                            image_attributes.other.insert(attribute_name, value);
+                        },
+
+                        // insert unknown attributes into layer attributes
+                        (_, value) => {
+                            layer_attributes.other.insert(attribute_name, value);
+                        },
+
+                    }
+                },
+
+                // in case the attribute value itself is not ok, but the rest of the image is
+                // only abort reading the image if desired
+                Err(error) => {
+                    if pedantic { return Err(error); }
+                }
+            }
+        }
+
+        // construct compression with parameters from properties
+        let compression = match (dwa_compression_level, compression) {
+            (Some(level), Some(Compression::DWAA(_))) => Some(Compression::DWAA(Some(level))),
+            (Some(level), Some(Compression::DWAB(_))) => Some(Compression::DWAB(Some(level))),
+            (_, other) => other,
+            // FIXME dwa compression level gets lost if any other compression is used later in the process
+        };
+
+        let compression = compression.ok_or(missing_attribute("compression"))?;
+        image_attributes.display_window = display_window.ok_or(missing_attribute("display window"))?;
+
+        let data_window = data_window.ok_or(missing_attribute("data window"))?;
+        data_window.validate(None)?; // validate now to avoid errors when computing the chunk_count
+        layer_attributes.layer_position = data_window.position;
+
+
+        // validate now to avoid errors when computing the chunk_count
+        if let Some(tiles) = tiles { tiles.validate()?; }
+        let blocks = match block_type {
+            None if requirements.is_single_layer_and_tiled => {
+                BlockDescription::Tiles(tiles.ok_or(missing_attribute("tiles"))?)
+            },
+            Some(BlockType::Tile) | Some(BlockType::DeepTile) => {
+                BlockDescription::Tiles(tiles.ok_or(missing_attribute("tiles"))?)
+            },
+
+            _ => BlockDescription::ScanLines,
+        };
+
+        let computed_chunk_count = compute_chunk_count(compression, data_window.size, blocks);
+        if chunk_count.is_some() && pedantic && chunk_count != Some(computed_chunk_count) {
+            return Err(Error::invalid("chunk count not matching data size"));
+        }
+
+        let header = Header {
+            compression,
+
+            // always compute ourselves, because we cannot trust anyone out there 😱
+            chunk_count: computed_chunk_count,
+
+            layer_size: data_window.size,
+
+            shared_attributes: image_attributes,
+            own_attributes: layer_attributes,
+
+            channels: channels.ok_or(missing_attribute("channels"))?,
+            line_order: line_order.unwrap_or(LineOrder::Unspecified),
+
+            blocks,
+            max_samples_per_pixel,
+            deep_data_version: version,
+            deep: block_type == Some(BlockType::DeepScanLine) || block_type == Some(BlockType::DeepTile),
+        };
+
+        Ok(header)
+    }
+
+    /// Without validation, write this instance to the byte stream.
+    pub fn write(&self, write: &mut impl Write) -> UnitResult {
+
+        macro_rules! write_attributes {
+            ( $($name: ident : $variant: ident = $value: expr),* ) => { $(
+                attribute::write($name, & $variant ($value .clone()), write)?; // TODO without clone
+            )* };
+        }
+
+        macro_rules! write_optional_attributes {
+            ( $($name: ident : $variant: ident = $value: expr),* ) => { $(
+                if let Some(value) = $value {
+                    attribute::write($name, & $variant (value.clone()), write)?; // TODO without clone
+                };
+            )* };
+        }
+
+        use crate::meta::header::standard_names::*;
+        use AttributeValue::*;
+
+        let (block_type, tiles) = match self.blocks {
+            BlockDescription::ScanLines => (attribute::BlockType::ScanLine, None),
+            BlockDescription::Tiles(tiles) => (attribute::BlockType::Tile, Some(tiles))
+        };
+
+        fn usize_as_i32(value: usize) -> AttributeValue {
+            I32(i32::try_from(value).expect("u32 exceeds i32 range"))
+        }
+
+        write_optional_attributes!(
+            TILES: TileDescription = &tiles,
+            DEEP_DATA_VERSION: I32 = &self.deep_data_version,
+            MAX_SAMPLES: usize_as_i32 = &self.max_samples_per_pixel
+        );
+
+        write_attributes!(
+            // chunks is not actually required, but always computed in this library anyways
+            CHUNKS: usize_as_i32 = &self.chunk_count,
+
+            BLOCK_TYPE: BlockType = &block_type,
+            CHANNELS: ChannelList = &self.channels,
+            COMPRESSION: Compression = &self.compression,
+            LINE_ORDER: LineOrder = &self.line_order,
+            DATA_WINDOW: IntegerBounds = &self.data_window(),
+
+            DISPLAY_WINDOW: IntegerBounds = &self.shared_attributes.display_window,
+            PIXEL_ASPECT: F32 = &self.shared_attributes.pixel_aspect,
+
+            WINDOW_CENTER: FloatVec2 = &self.own_attributes.screen_window_center,
+            WINDOW_WIDTH: F32 = &self.own_attributes.screen_window_width
+        );
+
+        write_optional_attributes!(
+            NAME: Text = &self.own_attributes.layer_name,
+            WHITE_LUMINANCE: F32 = &self.own_attributes.white_luminance,
+            ADOPTED_NEUTRAL: FloatVec2 = &self.own_attributes.adopted_neutral,
+            RENDERING_TRANSFORM: Text = &self.own_attributes.rendering_transform_name,
+            LOOK_MOD_TRANSFORM: Text = &self.own_attributes.look_modification_transform_name,
+            X_DENSITY: F32 = &self.own_attributes.horizontal_density,
+            OWNER: Text = &self.own_attributes.owner,
+            COMMENTS: Text = &self.own_attributes.comments,
+            CAPTURE_DATE: Text = &self.own_attributes.capture_date,
+            UTC_OFFSET: F32 = &self.own_attributes.utc_offset,
+            LONGITUDE: F32 = &self.own_attributes.longitude,
+            LATITUDE: F32 = &self.own_attributes.latitude,
+            ALTITUDE: F32 = &self.own_attributes.altitude,
+            FOCUS: F32 = &self.own_attributes.focus,
+            EXPOSURE_TIME: F32 = &self.own_attributes.exposure,
+            APERTURE: F32 = &self.own_attributes.aperture,
+            ISO_SPEED: F32 = &self.own_attributes.iso_speed,
+            ENVIRONMENT_MAP: EnvironmentMap = &self.own_attributes.environment_map,
+            KEY_CODE: KeyCode = &self.own_attributes.film_key_code,
+            TIME_CODE: TimeCode = &self.shared_attributes.time_code,
+            WRAP_MODES: Text = &self.own_attributes.wrap_mode_name,
+            FRAMES_PER_SECOND: Rational = &self.own_attributes.frames_per_second,
+            MULTI_VIEW: TextVector = &self.own_attributes.multi_view_names,
+            WORLD_TO_CAMERA: Matrix4x4 = &self.own_attributes.world_to_camera,
+            WORLD_TO_NDC: Matrix4x4 = &self.own_attributes.world_to_normalized_device,
+            DEEP_IMAGE_STATE: Rational = &self.own_attributes.deep_image_state,
+            ORIGINAL_DATA_WINDOW: IntegerBounds = &self.own_attributes.original_data_window,
+            CHROMATICITIES: Chromaticities = &self.shared_attributes.chromaticities,
+            PREVIEW: Preview = &self.own_attributes.preview,
+            VIEW: Text = &self.own_attributes.view_name,
+            NEAR: F32 = &self.own_attributes.near_clip_plane,
+            FAR: F32 = &self.own_attributes.far_clip_plane,
+            FOV_X: F32 = &self.own_attributes.horizontal_field_of_view,
+            FOV_Y: F32 = &self.own_attributes.vertical_field_of_view,
+            SOFTWARE: Text = &self.own_attributes.software_name
+        );
+
+        // dwa writes compression parameters as attribute.
+        match self.compression {
+            attribute::Compression::DWAA(Some(level)) |
+            attribute::Compression::DWAB(Some(level)) =>
+                attribute::write(DWA_COMPRESSION_LEVEL, &F32(level), write)?,
+
+            _ => {}
+        };
+
+
+        for (name, value) in &self.shared_attributes.other {
+            attribute::write(name.as_slice(), value, write)?;
+        }
+
+        for (name, value) in &self.own_attributes.other {
+            attribute::write(name.as_slice(), value, write)?;
+        }
+
+        sequence_end::write(write)?;
+        Ok(())
+    }
+
+    /// The rectangle describing the bounding box of this layer
+    /// within the infinite global 2D space of the file.
+    pub fn data_window(&self) -> IntegerBounds {
+        IntegerBounds::new(self.own_attributes.layer_position, self.layer_size)
+    }
+}
+
+
+
+/// Collection of required attribute names.
+pub mod standard_names {
+    macro_rules! define_required_attribute_names {
+        ( $($name: ident  :  $value: expr),* ) => {
+
+            /// A list containing all reserved names.
+            pub const ALL: &'static [&'static [u8]] = &[
+                $( $value ),*
+            ];
+
+            $(
+                /// The byte-string name of this required attribute as it appears in an exr file.
+                pub const $name: &'static [u8] = $value;
+            )*
+        };
+    }
+
+    define_required_attribute_names! {
+        TILES: b"tiles",
+        NAME: b"name",
+        BLOCK_TYPE: b"type",
+        DEEP_DATA_VERSION: b"version",
+        CHUNKS: b"chunkCount",
+        MAX_SAMPLES: b"maxSamplesPerPixel",
+        CHANNELS: b"channels",
+        COMPRESSION: b"compression",
+        DATA_WINDOW: b"dataWindow",
+        DISPLAY_WINDOW: b"displayWindow",
+        LINE_ORDER: b"lineOrder",
+        PIXEL_ASPECT: b"pixelAspectRatio",
+        WINDOW_CENTER: b"screenWindowCenter",
+        WINDOW_WIDTH: b"screenWindowWidth",
+        WHITE_LUMINANCE: b"whiteLuminance",
+        ADOPTED_NEUTRAL: b"adoptedNeutral",
+        RENDERING_TRANSFORM: b"renderingTransform",
+        LOOK_MOD_TRANSFORM: b"lookModTransform",
+        X_DENSITY: b"xDensity",
+        OWNER: b"owner",
+        COMMENTS: b"comments",
+        CAPTURE_DATE: b"capDate",
+        UTC_OFFSET: b"utcOffset",
+        LONGITUDE: b"longitude",
+        LATITUDE: b"latitude",
+        ALTITUDE: b"altitude",
+        FOCUS: b"focus",
+        EXPOSURE_TIME: b"expTime",
+        APERTURE: b"aperture",
+        ISO_SPEED: b"isoSpeed",
+        ENVIRONMENT_MAP: b"envmap",
+        KEY_CODE: b"keyCode",
+        TIME_CODE: b"timeCode",
+        WRAP_MODES: b"wrapmodes",
+        FRAMES_PER_SECOND: b"framesPerSecond",
+        MULTI_VIEW: b"multiView",
+        WORLD_TO_CAMERA: b"worldToCamera",
+        WORLD_TO_NDC: b"worldToNDC",
+        DEEP_IMAGE_STATE: b"deepImageState",
+        ORIGINAL_DATA_WINDOW: b"originalDataWindow",
+        DWA_COMPRESSION_LEVEL: b"dwaCompressionLevel",
+        PREVIEW: b"preview",
+        VIEW: b"view",
+        CHROMATICITIES: b"chromaticities",
+        NEAR: b"near",
+        FAR: b"far",
+        FOV_X: b"fieldOfViewHorizontal",
+        FOV_Y: b"fieldOfViewVertical",
+        SOFTWARE: b"software"
+    }
+}
+
+
+impl Default for LayerAttributes {
+    fn default() -> Self {
+        Self {
+            layer_position: Vec2(0, 0),
+            screen_window_center: Vec2(0.0, 0.0),
+            screen_window_width: 1.0,
+            layer_name: None,
+            white_luminance: None,
+            adopted_neutral: None,
+            rendering_transform_name: None,
+            look_modification_transform_name: None,
+            horizontal_density: None,
+            owner: None,
+            comments: None,
+            capture_date: None,
+            utc_offset: None,
+            longitude: None,
+            latitude: None,
+            altitude: None,
+            focus: None,
+            exposure: None,
+            aperture: None,
+            iso_speed: None,
+            environment_map: None,
+            film_key_code: None,
+            wrap_mode_name: None,
+            frames_per_second: None,
+            multi_view_names: None,
+            world_to_camera: None,
+            world_to_normalized_device: None,
+            deep_image_state: None,
+            original_data_window: None,
+            preview: None,
+            view_name: None,
+            software_name: None,
+            near_clip_plane: None,
+            far_clip_plane: None,
+            horizontal_field_of_view: None,
+            vertical_field_of_view: None,
+            other: Default::default()
+        }
+    }
+}
+
+impl std::fmt::Debug for LayerAttributes {
+    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let default_self = Self::default();
+
+        let mut debug = formatter.debug_struct("LayerAttributes (default values omitted)");
+
+        // always debug the following field
+        debug.field("name", &self.layer_name);
+
+        macro_rules! debug_non_default_fields {
+            ( $( $name: ident ),* ) => { $(
+
+                if self.$name != default_self.$name {
+                    debug.field(stringify!($name), &self.$name);
+                }
+
+            )* };
+        }
+
+        // only debug these fields if they are not the default value
+        debug_non_default_fields! {
+            screen_window_center, screen_window_width,
+            white_luminance, adopted_neutral, horizontal_density,
+            rendering_transform_name, look_modification_transform_name,
+            owner, comments,
+            capture_date, utc_offset,
+            longitude, latitude, altitude,
+            focus, exposure, aperture, iso_speed,
+            environment_map, film_key_code, wrap_mode_name,
+            frames_per_second, multi_view_names,
+            world_to_camera, world_to_normalized_device,
+            deep_image_state, original_data_window,
+            preview, view_name,
+            vertical_field_of_view, horizontal_field_of_view,
+            near_clip_plane, far_clip_plane, software_name
+        }
+
+        for (name, value) in &self.other {
+            debug.field(&format!("\"{}\"", name), value);
+        }
+
+        // debug.finish_non_exhaustive() TODO
+        debug.finish()
+    }
+}