EEVEE: Fix incorrect volumetric light shadowing

The shadowing was computed on the light distance squared,
leaking to much light since it was integrating the extinction behind
the ligth itself.

Also bump the maximum shadow max step to the actual UI values. Otherwise
we get shadowing under evaluated because `dd` is too small.

1 files changed, 4 insertions, 4 deletions

diff --git a/source/blender/draw/engines/eevee/shaders/volumetric_lib.glsl b/source/blender/draw/engines/eevee/shaders/volumetric_lib.glsl
index 9b852a57ec4..b1e3a40e8d2 100644
--- a/source/blender/draw/engines/eevee/shaders/volumetric_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/volumetric_lib.glsl
@@ -98,7 +98,7 @@ vec3 light_volume(LightData ld, vec4 l_vector)
   return tint * lum;
 }
 
-#define VOLUMETRIC_SHADOW_MAX_STEP 32.0
+#define VOLUMETRIC_SHADOW_MAX_STEP 128.0
 
 vec3 participating_media_extinction(vec3 wpos, sampler3D volume_extinction)
 {
@@ -115,10 +115,10 @@ vec3 light_volume_shadow(LightData ld, vec3 ray_wpos, vec4 l_vector, sampler3D v
 #if defined(VOLUME_SHADOW)
   /* Heterogeneous volume shadows */
   float dd = l_vector.w / volShadowSteps;
-  vec3 L = l_vector.xyz * l_vector.w;
+  vec3 L = l_vector.xyz / volShadowSteps;
   vec3 shadow = vec3(1.0);
-  for (float s = 0.5; s < VOLUMETRIC_SHADOW_MAX_STEP && s < (volShadowSteps - 0.1); s += 1.0) {
-    vec3 pos = ray_wpos + L * (s / volShadowSteps);
+  for (float s = 1.0; s < VOLUMETRIC_SHADOW_MAX_STEP && s <= volShadowSteps; s += 1.0) {
+    vec3 pos = ray_wpos + L * s;
     vec3 s_extinction = participating_media_extinction(pos, volume_extinction);
     shadow *= exp(-s_extinction * dd);
   }