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Fix gizmo line width issue when using perspective (#9067)

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# Objective

- In bevy_polyline, we discovered an issue that happens when line width
is smaller than 1.0 and using perspective. It would sometimes end up
negative or NaN. I'm not entirely sure _why_ it happens.

## Solution

- Make sure the width doesn't go below 0 before multiplying it with the
alpha

# Notes 

Here's a link to the bevy_polyline issue
https://github.com/ForesightMiningSoftwareCorporation/bevy_polyline/issues/46

I'm not sure if the solution is correct but it solved the issue in my
testing.

Co-authored-by: François <mockersf@gmail.com>
This commit is contained in:
IceSentry 2023-07-31 14:57:59 -04:00 committed by GitHub
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commit 0d7e81ee81
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1 changed files with 3 additions and 3 deletions
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6
crates/bevy_gizmos/src/lines.wgsl
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@ -64,7 +64,7 @@ fn vertex(vertex: VertexInput) -> VertexOutput {
#endif #endif
// Line thinness fade from https://acegikmo.com/shapes/docs/#anti-aliasing // Line thinness fade from https://acegikmo.com/shapes/docs/#anti-aliasing
if line_width < 1. { if line_width > 0.0 && line_width < 1. {
color.a *= line_width; color.a *= line_width;
line_width = 1.; line_width = 1.;
} }
@ -79,10 +79,10 @@ fn vertex(vertex: VertexInput) -> VertexOutput {
let epsilon = 4.88e-04; 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
// clip.w represents the near plane in homogeneous clip space in bevy, having a depth // clip.w represents the near plane in homogeneous clip space in bevy, having a depth
// 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));
} }