EEVEE-Next: HiZ Buffer: New implementation

This new implementation does all downsampling in a single compute shader
dispatch, removing a lot of complexity from the previous recursive
downsampling.

This is heavilly inspired by the Single-Pass-Downsampler from GPUOpen:
https://github.com/GPUOpen-Effects/FidelityFX-SPD
However I do not implement all the optimization bits as they require
vulkan (GL_KHR_shader_subgroup) and is not as versatile (it is only
for HiZ).

Timers inside renderdoc report ~0.4ms of saving on a 2048*1024 render for
the whole downsampling. Note that the previous implementation only
processed 6 mips where the new one processes 8 mips.
```
EEVEE ~1.0ms
EEVEE-Next ~0.6ms
```

Padding has been bumped to be of 128px for processing 8 mips.

A new debug option has been added (debug value 2) to validate the HiZ.

2 files changed, 12 insertions, 2 deletions

diff --git a/source/blender/draw/intern/DRW_gpu_wrapper.hh b/source/blender/draw/intern/DRW_gpu_wrapper.hh
index 5405afd2a90..b32fdedaeb9 100644
--- a/source/blender/draw/intern/DRW_gpu_wrapper.hh
+++ b/source/blender/draw/intern/DRW_gpu_wrapper.hh
@@ -562,6 +562,11 @@ class Texture : NonCopyable {
     return mip_views_[miplvl];
   }
 
+  int mip_count() const
+  {
+    return GPU_texture_mip_count(tx_);
+  }
+
   /**
    * Ensure the availability of mipmap views.
    * Layer views covers all layers of array textures.
diff --git a/source/blender/draw/intern/shaders/common_math_lib.glsl b/source/blender/draw/intern/shaders/common_math_lib.glsl
index e081a0243ca..e3734939b3f 100644
--- a/source/blender/draw/intern/shaders/common_math_lib.glsl
+++ b/source/blender/draw/intern/shaders/common_math_lib.glsl
@@ -130,12 +130,17 @@ void set_flag_from_test(inout int value, bool test, int flag) { if (test) { valu
 #define in_texture_range(texel, tex) \
   (all(greaterThanEqual(texel, ivec2(0))) && all(lessThan(texel, textureSize(tex, 0).xy)))
 
-uint divide_ceil_u(uint visible_count, uint divisor)
+uint divide_ceil(uint visible_count, uint divisor)
 {
   return (visible_count + (divisor - 1u)) / divisor;
 }
 
-int divide_ceil_i(int visible_count, int divisor)
+int divide_ceil(int visible_count, int divisor)
+{
+  return (visible_count + (divisor - 1)) / divisor;
+}
+
+ivec2 divide_ceil(ivec2 visible_count, ivec2 divisor)
 {
   return (visible_count + (divisor - 1)) / divisor;
 }