Fix T60170: Eevee: smoke color does not apply permanently

This was because color is not present in the density texture if there is
only one constant color. Adding it as a uniform.

source/blender/draw/engines/eevee/eevee_volumes.c

@@ -525,6 +525,13 @@ void EEVEE_volumes_cache_object_add(EEVEE_ViewLayerData *sldata, EEVEE_Data *ved
 			DRW_shgroup_uniform_texture_ref(grp, "sampflame", &sds->tex_flame);
 		}
 
+		/* Constant Volume color. */
+		static float white[3] = {1.0f, 1.0f, 1.0f};
+		bool use_constant_color = ((sds->active_fields & SM_ACTIVE_COLORS) == 0 &&
+		                           (sds->active_fields & SM_ACTIVE_COLOR_SET) != 0);
+
+		DRW_shgroup_uniform_vec3(grp, "volumeColor", (use_constant_color) ? sds->active_color : white, 1);
+
 		/* Output is such that 0..1 maps to 0..1000K */
 		DRW_shgroup_uniform_vec2(grp, "unftemperature", &sds->flame_ignition, 1);
 	}

source/blender/draw/engines/workbench/shaders/workbench_volume_frag.glsl

@@ -18,6 +18,7 @@ uniform float noiseOfs = 0.0f;
 uniform float stepLength; /* Step length in local space. */
 uniform float densityScale; /* Simple Opacity multiplicator. */
 uniform vec4 viewvecs[3];
+uniform vec3 activeColor;
 
 uniform float slicePosition;
 uniform int sliceAxis; /* -1 is no slice, 0 is X, 1 is Y, 2 is Z. */
@@ -135,7 +136,7 @@ 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) * activeColor;
 	extinction = max(1e-4, dot(scattering, vec3(0.33333)));
 
 	/* Scale shadows in log space and clamp them to avoid completely black shadows. */

source/blender/draw/engines/workbench/workbench_volume.c

@@ -191,10 +191,14 @@ void workbench_volume_cache_populate(WORKBENCH_Data *vedata, Scene *scene, Objec
 		DRW_shgroup_uniform_texture(grp, "transferTexture", sds->tex_coba);
 	}
 	else {
+		static float white[3] = {1.0f, 1.0f, 1.0f};
+		bool use_constant_color = ((sds->active_fields & SM_ACTIVE_COLORS) == 0 &&
+		                           (sds->active_fields & SM_ACTIVE_COLOR_SET) != 0);
 		DRW_shgroup_uniform_texture(grp, "densityTexture", sds->tex);
 		DRW_shgroup_uniform_texture(grp, "shadowTexture", sds->tex_shadow);
 		DRW_shgroup_uniform_texture(grp, "flameTexture", (sds->tex_flame) ? sds->tex_flame : e_data.dummy_tex);
 		DRW_shgroup_uniform_texture(grp, "flameColorTexture", (sds->tex_flame) ? sds->tex_flame_coba : e_data.dummy_coba_tex);
+		DRW_shgroup_uniform_vec3(grp, "activeColor", (use_constant_color) ? sds->active_color : white, 1);
 	}
 	DRW_shgroup_uniform_texture_ref(grp, "depthBuffer", &dtxl->depth);
 	DRW_shgroup_uniform_float_copy(grp, "densityScale", 10.0f * sds->display_thickness);

source/blender/gpu/shaders/gpu_shader_material.glsl

@@ -1701,6 +1701,8 @@ void node_attribute_volume_density(sampler3D tex, out vec4 outcol, out vec3 outv
 	outf = dot(vec3(1.0 / 3.0), outvec);
 }
 
+uniform vec3 volumeColor = vec3(1.0);
+
 void node_attribute_volume_color(sampler3D tex, out vec4 outcol, out vec3 outvec, out float outf)
 {
 #if defined(MESH_SHADER) && defined(VOLUMETRICS)
@@ -1714,7 +1716,7 @@ void node_attribute_volume_color(sampler3D tex, out vec4 outcol, out vec3 outvec
 	if (value.a > 1e-8)
 		value.rgb /= value.a;
 
-	outvec = value.rgb;
+	outvec = value.rgb * volumeColor;
 	outcol = vec4(outvec, 1.0);
 	outf = dot(vec3(1.0 / 3.0), outvec);
 }