EEVEE: Volumetrics: Add support for soft volumetric shadows

Soft surface shadows were already supported but now we support
soft shadows of the volume themselves.

This is only enabled if the light casts shadow and the scene soft
shadows toggle is enabled.

2 files changed, 15 insertions, 1 deletions

diff --git a/source/blender/draw/engines/eevee/shaders/common_uniforms_lib.glsl b/source/blender/draw/engines/eevee/shaders/common_uniforms_lib.glsl
index b3174afc799..d7996ab4bd1 100644
--- a/source/blender/draw/engines/eevee/shaders/common_uniforms_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/common_uniforms_lib.glsl
@@ -12,9 +12,9 @@ layout(std140) uniform common_block
   vec4 volJitter;
   vec4 volCoordScale; /* To convert volume uvs to screen uvs */
   float volHistoryAlpha;
-  float volLightClamp;
   float volShadowSteps;
   bool volUseLights;
+  bool volUseSoftShadows;
   /* Screen Space Reflections */
   vec4 ssrParameters;
   float ssrBorderFac;
diff --git a/source/blender/draw/engines/eevee/shaders/volumetric_lib.glsl b/source/blender/draw/engines/eevee/shaders/volumetric_lib.glsl
index 6d7ddd4e56e..11fd3418a72 100644
--- a/source/blender/draw/engines/eevee/shaders/volumetric_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/volumetric_lib.glsl
@@ -127,6 +127,20 @@ vec3 participating_media_extinction(vec3 wpos, sampler3D volume_extinction)
 vec3 light_volume_shadow(LightData ld, vec3 ray_wpos, vec4 l_vector, sampler3D volume_extinction)
 {
 #if defined(VOLUME_SHADOW)
+  /* If light is shadowed, use the shadow vector, if not, reuse the light vector. */
+  if (volUseSoftShadows && ld.l_shadowid >= 0.0) {
+    ShadowData sd = shadows_data[int(ld.l_shadowid)];
+
+    if (ld.l_type == SUN) {
+      l_vector.xyz = shadows_cascade_data[int(sd.sh_data_index)].sh_shadow_vec;
+      /* No need for length, it is recomputed later. */
+    }
+    else {
+      l_vector.xyz = shadows_cube_data[int(sd.sh_data_index)].position.xyz - ray_wpos;
+      l_vector.w = length(l_vector.xyz);
+    }
+  }
+
   /* Heterogeneous volume shadows */
   float dd = l_vector.w / volShadowSteps;
   vec3 L = l_vector.xyz / volShadowSteps;