EEVEE-Next: Remove slope and quantization biases

This avoid self intersection during tracing which expect
unbiased depth. We compensate by adding a 1.5 shadow pixel
offset in the normal direction which is enough to fix
most remaining self shadowing. But another bias parameter
will likely need to be added anyway.

Fixes #121194

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

@@ -107,6 +107,21 @@ float light_attenuation_common(LightData light, const bool is_directional, vec3
   return 1.0;
 }
 
+float light_shape_radius(LightData light)
+{
+
+  float radius;
+  if (is_sun_light(light.type)) {
+    return light_sun_data_get(light).radius;
+  }
+  else if (is_area_light(light.type)) {
+    return length(light_area_data_get(light).size);
+  }
+  else {
+    return light_spot_data_get(light).radius;
+  }
+}
+
 /**
  * Fade light influence when surface is not facing the light.
  * This is needed because LTC leaks light at roughness not 0 or 1
@@ -126,18 +141,8 @@ float light_attenuation_facing(LightData light,
     return 1.0;
   }
 
-  float radius;
-  if (is_sun_light(light.type)) {
-    radius = light_sun_data_get(light).radius;
-  }
-  else if (is_area_light(light.type)) {
-    radius = length(light_area_data_get(light).size);
-  }
-  else {
-    radius = light_spot_data_get(light).radius;
-  }
   /* Sine of angle between light center and light edge. */
-  float sin_solid_angle = radius / distance_to_light;
+  float sin_solid_angle = light_shape_radius(light) / distance_to_light;
   /* Sine of angle between light center and shading plane. */
   float sin_light_angle = dot(L, Ng);
   /* Do attenuation after the horizon line to avoid harsh cut

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

@@ -486,7 +486,10 @@ float shadow_normal_offset(float texel_radius, vec3 Ng, vec3 L)
   /* TODO: Should we take the light shape into consideration? */
   float cos_theta = abs(dot(Ng, L));
   float sin_theta = sqrt(saturate(1.0 - square(cos_theta)));
-  return texel_radius * sin_theta;
+  /* Note that we still bias by one pixel anyway to fight quantization artifacts.
+   * This helps with self intersection of slopped surfaces and gives softer soft shadow (?! why).
+   * FIXME: This is likely to hide some issue, and we need a user facing bias parameter anyway. */
+  return texel_radius * (sin_theta + 3.0);
 }
 
 /**

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

@@ -29,8 +29,6 @@ void main()
    * Note that we always need a minimum slope bias of 1 pixel to avoid slanted surfaces aliasing
    * onto facing surfaces.
    * IMPORTANT: `fwidth` needs to be inside uniform control flow. */
-  f_depth += fwidth(f_depth) * shadow_flat.filter_radius;
-
 #ifdef SHADOW_UPDATE_TBDR
 /* We need to write to `gl_FragDepth` un-conditionally. So we cannot early exit or use discard. */
 #  define discard_result f_depth = 1.0;
@@ -86,8 +84,6 @@ void main()
   ivec3 out_texel = ivec3((page.xy << page_shift) | texel_page, page.z);
 
   uint u_depth = floatBitsToUint(f_depth);
-  /* Quantization bias. Equivalent to `nextafter()` in C without all the safety. */
-  u_depth += 2;
   imageAtomicMin(shadow_atlas_img, out_texel, u_depth);
 #endif