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compute world_from_cascade analytically #20364

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Aug 5, 2025
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compute world_from_cascade analytically #20364

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20 changes: 13 additions & 7 deletions crates/bevy_light/src/cascade.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -302,16 +302,22 @@ fn calculate_cascade(
max.z,
);

// It is critical for `world_to_cascade` to be stable. So rather than forming `cascade_to_world`
// It is critical for `cascade_from_world` to be stable. So rather than forming `world_from_cascade`
// and inverting it, which risks instability due to numerical precision, we directly form
// `world_to_cascade` as the reference material suggests.
let light_to_world_transpose = world_from_light.transpose();
// `cascade_from_world` as the reference material suggests.
let world_from_light_transpose = world_from_light.transpose();
let cascade_from_world = Mat4::from_cols(
light_to_world_transpose.x_axis,
light_to_world_transpose.y_axis,
light_to_world_transpose.z_axis,
world_from_light_transpose.x_axis,
world_from_light_transpose.y_axis,
world_from_light_transpose.z_axis,
(-near_plane_center).extend(1.0),
);
let world_from_cascade = Mat4::from_cols(
world_from_light.x_axis,
world_from_light.y_axis,
world_from_light.z_axis,
world_from_light * near_plane_center.extend(1.0),
);

// Right-handed orthographic projection, centered at `near_plane_center`.
// NOTE: This is different from the reference material, as we use reverse Z.
Expand All @@ -325,7 +331,7 @@ fn calculate_cascade(

let clip_from_world = clip_from_cascade * cascade_from_world;
Cascade {
world_from_cascade: cascade_from_world.inverse(),
world_from_cascade,
clip_from_cascade,
clip_from_world,
texel_size: cascade_texel_size,
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