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Fix log depth z fighting #6513

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merged 2 commits into from
Apr 30, 2018
Merged

Fix log depth z fighting #6513

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b5ba893
Fix z-fighting for classification primitives.
bagnell Apr 27, 2018
e1553dc
Merge remote-tracking branch 'origin/master' into z-fighting
emackey Apr 30, 2018
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3 changes: 2 additions & 1 deletion Source/Scene/ClassificationPrimitive.js
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Expand Up @@ -530,7 +530,8 @@ define([
// Tesselation on ClassificationPrimitives tends to be low,
// which causes problems when interpolating log depth from vertices.
// So force computing and writing logarithmic depth in the fragment shader.
var disableGlPositionLogDepth = 'DISABLE_GL_POSITION_LOG_DEPTH';
// Re-enable at far distances to avoid z-fighting.
var disableGlPositionLogDepth = 'ENABLE_GL_POSITION_LOG_DEPTH_AT_HEIGHT';

var vsSource = new ShaderSource({
defines : [extrudedDefine, disableGlPositionLogDepth],
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7 changes: 7 additions & 0 deletions Source/Shaders/Builtin/Functions/vertexLogDepth.glsl
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Expand Up @@ -7,6 +7,13 @@ void czm_updatePositionDepth() {
#if defined(LOG_DEPTH) && !defined(DISABLE_GL_POSITION_LOG_DEPTH)
v_logPositionEC = (czm_inverseProjection * gl_Position).xyz;

#ifdef ENABLE_GL_POSITION_LOG_DEPTH_AT_HEIGHT
if (length(v_logPositionEC) < 2.0e6)
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The fix works... I'm just wondering if there is anything special about 2.0e6 or if it just happens to be a good value.

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I zoomed in to the edge of the polygon and slowly zoomed out until I saw the z fighting. Tested with larger and smaller polygons than what was in the bug example.

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Alright, thanks!

{
return;
}
#endif

gl_Position.z = log2(max(1e-6, 1.0 + gl_Position.w)) * czm_logFarDistance - 1.0;
gl_Position.z *= gl_Position.w;
#endif
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