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/**
* Shader that down-sample depth buffer,
* saving min and max value of each texel in the above mipmaps.
* Adapted from http://rastergrid.com/blog/2010/10/hierarchical-z-map-based-occlusion-culling/
*/
#ifdef LAYERED
uniform sampler2DArray depthBuffer;
uniform int depthLayer;
#else
uniform sampler2D depthBuffer;
#endif
#ifdef LAYERED
# define sampleLowerMip(t) texelFetch(depthBuffer, ivec3(t, depthLayer), 0).r
# define gatherLowerMip(t) textureGather(depthBuffer, vec3(t, depthLayer))
#else
# define sampleLowerMip(t) texelFetch(depthBuffer, t, 0).r
# define gatherLowerMip(t) textureGather(depthBuffer, t)
#endif
#ifdef MIN_PASS
# define minmax2(a, b) min(a, b)
# define minmax3(a, b, c) min(min(a, b), c)
# define minmax4(a, b, c, d) min(min(min(a, b), c), d)
#else /* MAX_PASS */
# define minmax2(a, b) max(a, b)
# define minmax3(a, b, c) max(max(a, b), c)
# define minmax4(a, b, c, d) max(max(max(a, b), c), d)
#endif
/* On some AMD card / driver combination, it is needed otherwise,
* the shader does not write anything. */
#if defined(GPU_INTEL) || defined(GPU_ATI)
out vec4 fragColor;
#endif
void main()
{
ivec2 texelPos = ivec2(gl_FragCoord.xy);
ivec2 mipsize = textureSize(depthBuffer, 0).xy;
#ifndef COPY_DEPTH
texelPos *= 2;
#endif
#ifdef COPY_DEPTH
float val = sampleLowerMip(texelPos);
#else
vec4 samp;
# ifdef GPU_ARB_texture_gather
/* + 1.0 to gather at the center of target 4 texels. */
samp = gatherLowerMip((vec2(texelPos) + 1.0) / vec2(mipsize));
# else
samp.x = sampleLowerMip(texelPos);
samp.y = sampleLowerMip(texelPos + ivec2(1, 0));
samp.z = sampleLowerMip(texelPos + ivec2(1, 1));
samp.w = sampleLowerMip(texelPos + ivec2(0, 1));
# endif
float val = minmax4(samp.x, samp.y, samp.z, samp.w);
/* if we are reducing an odd-width texture then fetch the edge texels */
if (((mipsize.x & 1) != 0) && (texelPos.x == mipsize.x - 3)) {
/* if both edges are odd, fetch the top-left corner texel */
if (((mipsize.y & 1) != 0) && (texelPos.y == mipsize.y - 3)) {
samp.x = sampleLowerMip(texelPos + ivec2(2, 2));
val = minmax2(val, samp.x);
}
# ifdef GPU_ARB_texture_gather
samp = gatherLowerMip((vec2(texelPos) + vec2(2.0, 1.0)) / vec2(mipsize));
# else
samp.y = sampleLowerMip(texelPos + ivec2(2, 0));
samp.z = sampleLowerMip(texelPos + ivec2(2, 1));
# endif
val = minmax3(val, samp.y, samp.z);
}
/* if we are reducing an odd-height texture then fetch the edge texels */
if (((mipsize.y & 1) != 0) && (texelPos.y == mipsize.y - 3)) {
# ifdef GPU_ARB_texture_gather
samp = gatherLowerMip((vec2(texelPos) + vec2(1.0, 2.0)) / vec2(mipsize));
# else
samp.x = sampleLowerMip(texelPos + ivec2(0, 2));
samp.y = sampleLowerMip(texelPos + ivec2(1, 2));
# endif
val = minmax3(val, samp.x, samp.y);
}
#endif
#if defined(GPU_INTEL) || defined(GPU_ATI)
/* Use color format instead of 24bit depth texture */
fragColor = vec4(val);
#endif
gl_FragDepth = val;
}
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