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.