Hello there. 
Hope you have a good day!
To solve “peter panning” problem I try to perform glPolygonOffset().
That gives so good results that I became almost happy.
But one frustrating problem appears: it conflicts with “Shadow Map Silhouette Revectorization” technique I implemented before.
The point is I need to determine the center of shadow texel in view space.
Before I calculated it easily by reprojecting point from shadow map to view space.
But now depth map loose exact dept because of details of glPolygonOffset:
The offset is added before the depth test is performed and before the value is written into the depth buffer.
Thus I can not calculate offsets in view space for shadow texels.
Is there a way to calculate the center of the shadow texel in view space without dept map values?
May be I can have origin and modified depth at the same rendering pass?
May be exists the third way to do that?
Thank for any answer!
It is possible to store a diff generated by glPolygonOffet to separate buffer and keep real data in depth buffer at the same pass?
May be I want to strange stuff, but separate pass to get offset is very expensive, also a custom offset generation is to expensive too even if using early depth test.
Found and implemented solution.
Build composite frame buffer with depth and color textures.
While rendering depth map:
- Render adapted depth data directly in depth buffer.
- Calculate real depth value in attached fragment shader.
The most difficult was correct calculation of depth:
#version 430
out vec4 fragColor;
in VBlock {
vec4 position;
} vIn;
void main() {
float far = gl_DepthRange.far;
float near = gl_DepthRange.near;
vec4 pos = vIn.position;
float val = pos.z / pos.w;
float depth = (((far - near) * val) + near + far) / 2.0;
fragColor = vec4(depth, 0, 0, 1.0);
}
That little bit slower than default depth mapping (without fragment shader) +6 ms.
But much much faster that 2 different passes.
The glPolygonOffet let me dramatically improve shadow quality avoiding any “peter panning”
The very good result for me.
