1. A concise explanation of the problem you’re experiencing.
When reversing the rendering pipeline in a post-processing fragement shader, different matrices that should be isomorphic behave differently.
2. A minimal code example.
As far as I can tell worldPos and otherWorldPos are not the same, but should be (roughly, allowing for floating point inaccuracies).
vec2 screenPos = (gl_FragCoord.xy / czm_viewport.zw) * 2.0 - 1.0;
vec4 clipPos = vec4(screenPos, 1.0, 1.0) / gl_FragCoord.w;
vec4 eyePos = czm_inverseProjection * clipPos;
vec4 worldPos = czm_inverseView * eyePos; vec4 otherWorldPos = czm_inverseViewProjection * clipPos; gl_FragColor = length(normalize(otherWorldPos) - normalize(worldPos)) < 0.1 ? vec4(1.0) // should be white : vec4(0.0); // is in fact mostly black, but not completely O.o
When using worldPos I get sensible results for my further calculations (see my panorama rendering question), but not when using otherWorldPos.
I was just trying to use the most efficient way to compute world coordinates to do “rendering” of a panorama in a fragment shader and was really confused that I got garbage results.
4. The Cesium version you’re using, your operating system and browser.
Firefox Nightly & Google chrome