OpenGL Smoke: fix color issue, and clarify meaning of variables in the shader.

1 files changed, 16 insertions, 22 deletions

diff --git a/source/blender/gpu/shaders/gpu_shader_smoke_frag.glsl b/source/blender/gpu/shaders/gpu_shader_smoke_frag.glsl
index c467925725d..7bee7ef47a7 100644
--- a/source/blender/gpu/shaders/gpu_shader_smoke_frag.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_smoke_frag.glsl
@@ -1,8 +1,9 @@
 
 varying vec3 coords;
 
-uniform vec4 active_color;
-uniform float cell_spacing;
+uniform vec3 active_color;
+uniform float step_size;
+uniform float density_scale;
 
 uniform sampler3D soot_texture;
 uniform sampler3D shadow_texture;
@@ -14,34 +15,27 @@ uniform sampler1D spectrum_texture;
 
 void main()
 {
+	/* compute color and density from volume texture */
 	vec4 soot = texture3D(soot_texture, coords);
+	vec3 soot_color = active_color * soot.rgb / soot.a;
+	float soot_density = density_scale * soot.a;
 
-	/* unpremultiply volume texture */
-	float value = 1.0f / soot.a;
-	soot.xyz *= vec3(value);
+	/* compute transmittance and alpha */
+	float soot_transmittance = pow(2.71828182846, -soot_density * step_size);
+	float soot_alpha = 1.0 - soot_transmittance;
 
-	/* calculate shading factor from soot */
-	value = soot.a * active_color.a;
-	value *= cell_spacing;
-	value *= 1.442695041;
-	soot = vec4(pow(2.0, -value));
-
-	/* alpha */
-	soot.a = 1.0 - soot.r;
-
-	/* shade colors */
-	vec3 shadow = texture3D(shadow_texture, coords).rrr;
-	soot.xyz *= shadow;
-	soot.xyz *= active_color.xyz;
+	/* shade */
+	float shadow = texture3D(shadow_texture, coords).r;
+	soot_color *= soot_transmittance * shadow;
 
 	/* premultiply alpha */
-	vec4 color = vec4(soot.a * soot.rgb, soot.a);
+	vec4 color = vec4(soot_alpha * soot_color, soot_alpha);
 
 #ifdef USE_FIRE
-	/* blend in fire */
+	/* fire */
 	float flame = texture3D(flame_texture, coords).r;
-	vec4 spec = texture1D(spectrum_texture, flame);
-	color = vec4(color.rgb + (1 - color.a) * spec.a * spec.rgb, color.a);
+	vec4 emission = texture1D(spectrum_texture, flame);
+	color.rgb += (1 - color.a) * emission.a * emission.rgb;
 #endif
 
 	gl_FragColor = color;