84 lines
2.7 KiB
Text
84 lines
2.7 KiB
Text
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/*
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* Logarithmic depth buffer utility functions
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*
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* The HDR pipeline uses a logarithmic depth buffer to avoid Z-fighting and
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* depth precision issues. This method is compatible with all OpenGL 3.3
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* hardware since it does not require any fancy depth reversal tricks.
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*
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* The main disadvantage is that we lose the early depth test optimization. This
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* is not a problem for us because we use deferred rendering, so the fragment
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* shaders that run on the actual geometry are very lightweight.
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*
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* Sources:
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* https://outerra.blogspot.com/2009/08/logarithmic-z-buffer.html
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* https://outerra.blogspot.com/2012/11/maximizing-depth-buffer-range-and.html
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* https://outerra.blogspot.com/2013/07/logarithmic-depth-buffer-optimizations.html
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* https://io7m.github.io/r2/documentation/p2s24.xhtml
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*/
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#version 330 core
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uniform float fg_Fcoef;
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uniform vec2 fg_NearFar;
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/*
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* Prepare a view space depth value for encoding. Normal usage involves calling
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* this function in the vertex shader, after writing to gl_Position. The z value
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* corresponds to gl_Position.w (if using perspective projection), or the
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* negated view space depth.
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* See logdepth_encode().
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*/
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float logdepth_prepare_vs_depth(float z)
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{
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return 1.0 + z;
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}
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/*
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* Encodes a given depth value obtained with logdepth_prepare_vs_depth() into
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* logarithmic depth. The result is used in the fragment shader to write to
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* gl_FragDepth.
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*/
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float logdepth_encode(float z)
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{
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float half_fcoef = fg_Fcoef * 0.5;
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float clamped_z = max(1e-6, z);
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return log2(clamped_z) * half_fcoef;
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}
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/*
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* This is an alternative way of encoding a depth value obtained with
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* logdepth_prepare_vs_depth() into logarithmic depth in the vertex shader
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* without writing to gl_FragDepth in the fragment shader. The result
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* corresponds to gl_Position.z
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*
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* The disadvantage is that depth will not be interpolated in a
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* perspectively-correct way, but it will work okay for very finely tessellated
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* geometry.
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*/
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float logdepth_encode_no_perspective(float z)
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{
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float clamped_z = max(1e-6, z);
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return log2(clamped_z) * fg_Fcoef - 1.0;
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}
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/*
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* Decode a view space depth value that was encoded with the functions above.
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* z corresponds to the [0,1] depth buffer value.
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* NOTE: The resulting depth value is positive, so it must be negated to yield
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* a conventional negative view space depth value.
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*/
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float logdepth_decode(float z)
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{
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float half_fcoef = fg_Fcoef * 0.5;
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float exponent = z / half_fcoef;
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return pow(2.0, exponent) - 1.0;
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}
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/*
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* Same as logdepth_decode(), but returns the normalized view-space depth
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* in the [0,1] range.
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*/
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float logdepth_decode_normalized(float z)
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{
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return logdepth_decode(z) / fg_NearFar.y;
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}
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