Workbench: Scale shadowing based on density

This makes previewing thick smoke a bit more plausible with better shadows.

The shadowing is clamped so that nothing is completely black. That said the
lower bound is pretty low.

This is not an option but could become one if users do not like it in
all situations.

1 files changed, 4 insertions, 2 deletions

diff --git a/source/blender/draw/engines/workbench/shaders/workbench_volume_frag.glsl b/source/blender/draw/engines/workbench/shaders/workbench_volume_frag.glsl
index f14078a71eb..0bb6af40647 100644
--- a/source/blender/draw/engines/workbench/shaders/workbench_volume_frag.glsl
+++ b/source/blender/draw/engines/workbench/shaders/workbench_volume_frag.glsl
@@ -135,10 +135,12 @@ void volume_properties(vec3 ls_pos, out vec3 scattering, out float extinction)
 	float shadows = sample_volume_texture(shadowTexture, co).r;
 	vec4 density = sample_volume_texture(densityTexture, co); /* rgb: color, a: density */
 
-	scattering = density.rgb * density.a * densityScale;
+	scattering = density.rgb * (density.a * densityScale);
 	extinction = max(1e-4, dot(scattering, vec3(0.33333)));
 
-	scattering *= shadows * M_PI;
+	/* Scale shadows in log space and clamp them to avoid completely black shadows. */
+	scattering *= exp(clamp(log(shadows) * densityScale * 0.1, -2.5, 0.0)) * M_PI;
+
 	/* 800 is arbitrary and here to mimic old viewport. TODO make it a parameter */
 	scattering += pow(emission.rgb, vec3(2.2)) * emission.a * 800.0;
 #endif