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Fix float precision issue in the gizmo shader (#10408)

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Fix a precision issue with in the manual near-clipping function.
This only affected lines that span large distances (starting at 100_000~
units) in my testing.

Fixes #10403
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irate 2023-11-14 23:36:02 +01:00 committed by GitHub
parent b1fd9eddbb
commit 7b2213a5f3
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1 changed files with 7 additions and 4 deletions
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11
crates/bevy_gizmos/src/lines.wgsl
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@ -28,6 +28,8 @@ struct VertexOutput {
@location(0) color: vec4<f32>, @location(0) color: vec4<f32>,
}; };
const EPSILON: f32 = 4.88e-04;
@vertex @vertex
fn vertex(vertex: VertexInput) -> VertexOutput { fn vertex(vertex: VertexInput) -> VertexOutput {
var positions = array<vec3<f32>, 6>( var positions = array<vec3<f32>, 6>(
@ -79,7 +81,6 @@ fn vertex(vertex: VertexInput) -> VertexOutput {
if line_gizmo.depth_bias >= 0. { if line_gizmo.depth_bias >= 0. {
depth = clip.z * (1. - line_gizmo.depth_bias); depth = clip.z * (1. - line_gizmo.depth_bias);
} else { } else {
let epsilon = 4.88e-04;
// depth * (clip.w / depth)^-depth_bias. So that when -depth_bias is 1.0, this is equal to clip.w // depth * (clip.w / depth)^-depth_bias. So that when -depth_bias is 1.0, this is equal to clip.w
// and when equal to 0.0, it is exactly equal to depth. // and when equal to 0.0, it is exactly equal to depth.
// the epsilon is here to prevent the depth from exceeding clip.w when -depth_bias = 1.0 // the epsilon is here to prevent the depth from exceeding clip.w when -depth_bias = 1.0
@ -87,7 +88,7 @@ fn vertex(vertex: VertexInput) -> VertexOutput {
// of this value means nothing can be in front of this // of this value means nothing can be in front of this
// The reason this uses an exponential function is that it makes it much easier for the // The reason this uses an exponential function is that it makes it much easier for the
// user to chose a value that is convenient for them // user to chose a value that is convenient for them
depth = clip.z * exp2(-line_gizmo.depth_bias * log2(clip.w / clip.z - epsilon)); depth = clip.z * exp2(-line_gizmo.depth_bias * log2(clip.w / clip.z - EPSILON));
} }
var clip_position = vec4(clip.w * ((2. * screen) / resolution - 1.), depth, clip.w); var clip_position = vec4(clip.w * ((2. * screen) / resolution - 1.), depth, clip.w);
@ -101,8 +102,10 @@ fn clip_near_plane(a: vec4<f32>, b: vec4<f32>) -> vec4<f32> {
// Interpolate a towards b until it's at the near plane. // Interpolate a towards b until it's at the near plane.
let distance_a = a.z - a.w; let distance_a = a.z - a.w;
let distance_b = b.z - b.w; let distance_b = b.z - b.w;
let t = distance_a / (distance_a - distance_b); // Add an epsilon to the interpolator to ensure that the point is
return a + (b - a) * t; // not just behind the clip plane due to floating-point imprecision.
let t = distance_a / (distance_a - distance_b) + EPSILON;
return mix(a, b, t);
} }
return a; return a;
} }