1 files changed, 40 insertions, 0 deletions
diff --git a/source/blender/draw/engines/eevee/shaders/eevee_hiz_downsample_frag.glsl b/source/blender/draw/engines/eevee/shaders/eevee_hiz_downsample_frag.glsl
new file mode 100644
index 00000000000..9a095d960b2
--- /dev/null
+++ b/source/blender/draw/engines/eevee/shaders/eevee_hiz_downsample_frag.glsl
@@ -0,0 +1,40 @@
+/**
+ * Shader that down-sample depth buffer, creating a Hierarchical-Z buffer.
+ * Saves max value of each 2x2 texel in the mipmap above the one we are rendering to.
+ * Adapted from http://rastergrid.com/blog/2010/10/hierarchical-z-map-based-occlusion-culling/
+ *
+ * Major simplification has been made since we pad the buffer to always be bigger than input to
+ * avoid mipmapping misalignement.
+ */
+
+#pragma BLENDER_REQUIRE(common_math_lib.glsl)
+
+uniform sampler2D depth_tx;
+
+uniform vec2 texel_size;
+
+layout(location = 0) out float out_depth;
+
+#ifndef GPU_ARB_texture_gather
+vec4 texGather(sampler2D tex, vec2 uv)
+{
+  vec4 ofs = vec2(0.5, 0.5, -0.5, -0.5) * texel_size.xyxy;
+  return vec4(texture(tex, uv + ofs.zw).r,
+              texture(tex, uv + ofs.zy).r,
+              texture(tex, uv + ofs.xw).r,
+              texture(tex, uv + ofs.xy).r);
+}
+#else
+#  define texGather(a, b) textureGather(a, b)
+#endif
+
+void main()
+{
+  /* NOTE(@fclem): textureSize() does not work the same on all implementations
+   * when changing the min and max texture levels. Use uniform instead (see T87801). */
+  vec2 uv = gl_FragCoord.xy * texel_size;
+
+  vec4 samp = texGather(depth_tx, uv);
+
+  out_depth = max_v4(samp);
+}