EEVEE-Next: Precompute AO/GI quality factor

This avoid some ALU in hot loops of expensive shaders.

source/blender/draw/engines/eevee_next/eevee_ambient_occlusion.cc

@@ -42,7 +42,7 @@ void AmbientOcclusion::init()
 
   data_.distance = sce_eevee.gtao_distance;
   data_.gi_distance = (sce_eevee.fast_gi_distance > 0.0f) ? sce_eevee.fast_gi_distance : 1e16f;
-  data_.quality = sce_eevee.gtao_quality;
+  data_.lod_factor = 1.0f / (1.0f + sce_eevee.gtao_quality * 4.0f);
   data_.thickness = sce_eevee.gtao_thickness;
   data_.angle_bias = 1.0 / max_ff(1e-8f, 1.0 - sce_eevee.gtao_focus);
   /* Size is multiplied by 2 because it is applied in NDC [-1..1] range. */

source/blender/draw/engines/eevee_next/eevee_shader_shared.hh

@@ -1932,7 +1932,7 @@ BLI_STATIC_ASSERT_ALIGN(RayTraceData, 16)
 struct AOData {
   float2 pixel_size;
   float distance;
-  float quality;
+  float lod_factor;
 
   float thickness;
   float angle_bias;

source/blender/draw/engines/eevee_next/shaders/eevee_ambient_occlusion_lib.glsl

@@ -105,7 +105,7 @@ float ambient_ambient_occlusion_search_horizon(vec3 vI,
     /* Gives us good precision at center and ensure we cross at least one pixel per iteration. */
     time = 1.0 + iter + square((iter + noise) / sample_count) * ssray.max_time;
     float stride = time - prev_time;
-    float lod = (log2(stride) - noise) / (1.0 + uniform_buf.ao.quality);
+    float lod = (log2(stride) - noise) * uniform_buf.ao.lod_factor;
 
     vec2 uv = ssray.origin.xy + ssray.direction.xy * time;
     float depth = textureLod(depth_tx, uv * uniform_buf.hiz.uv_scale, floor(lod)).r;

source/blender/draw/engines/eevee_next/shaders/eevee_horizon_scan_eval_lib.glsl

@@ -169,7 +169,7 @@ HorizonScanResult horizon_scan_eval(vec3 vP,
           time += 1.0;
         }
 
-        float lod = 1.0 + (float(j >> 2) / (1.0 + uniform_buf.ao.quality));
+        float lod = 1.0 + float(j >> 2) * uniform_buf.ao.lod_factor;
 
         vec2 sample_uv = ssray.origin.xy + ssray.direction.xy * time;
         float sample_depth = textureLod(hiz_tx, sample_uv * uniform_buf.hiz.uv_scale, lod).r;