diff options
Diffstat (limited to 'crates/fparkan-render/src/lib.rs')
| -rw-r--r-- | crates/fparkan-render/src/lib.rs | 40 |
1 files changed, 40 insertions, 0 deletions
diff --git a/crates/fparkan-render/src/lib.rs b/crates/fparkan-render/src/lib.rs index ad96204..2ad4789 100644 --- a/crates/fparkan-render/src/lib.rs +++ b/crates/fparkan-render/src/lib.rs @@ -349,6 +349,23 @@ pub enum LegacyDepthMode { TestReadOnly, } +/// Reflects world Z before a row-vector clip transform, preserving points on the plane. +#[must_use] +pub fn reflect_clip_from_world_about_z(matrix: [f32; 16], height: f32) -> Option<[f32; 16]> { + if !height.is_finite() || !matrix.iter().all(|value| value.is_finite()) { + return None; + } + let mut reflected = matrix; + for column in 0..4 { + reflected[8 + column] = -matrix[8 + column]; + reflected[12 + column] = matrix[12 + column] + 2.0 * height * matrix[8 + column]; + } + reflected + .iter() + .all(|value| value.is_finite()) + .then_some(reflected) +} + /// Triangle culling behaviour represented without a graphics API type. #[derive(Clone, Copy, Debug, Default, Eq, PartialEq)] pub enum LegacyCullMode { @@ -556,6 +573,29 @@ mod tests { result } + #[test] + fn water_reflection_preserves_the_plane_and_reverses_height_before_projection() { + let matrix = [ + 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, + ]; + let reflected = reflect_clip_from_world_about_z(matrix, 150.0).unwrap(); + let project = |m: [f32; 16], p: [f32; 4]| -> [f32; 4] { + std::array::from_fn(|column| (0..4).map(|row| p[row] * m[row * 4 + column]).sum()) + }; + for z in [125.0, 150.0, 185.0] { + assert_eq!( + project(reflected, [7.0, 11.0, z, 1.0]), + project(matrix, [7.0, 11.0, 300.0 - z, 1.0]) + ); + } + assert_eq!( + reflect_clip_from_world_about_z(reflected, 150.0), + Some(matrix) + ); + assert!(reflect_clip_from_world_about_z(matrix, f32::NAN).is_none()); + assert!(reflect_clip_from_world_about_z([f32::MAX; 16], f32::MAX).is_none()); + } + fn assert_matrix_approximately_identity(matrix: [f32; 16]) { for (index, value) in matrix.into_iter().enumerate() { let expected = if index / 4 == index % 4 { 1.0 } else { 0.0 }; |