Properly handle vertex color color space for Cycles GLSL

A bit tricky, need to pass additional information about what the attribute
is and how to deal with it.

BI path stays unchanged, just to make things simplier for now.

Fixes T48555: Cycles GLSL- Incorrect Vertex Color results from Attribute node

7 files changed, 70 insertions, 4 deletions

diff --git a/source/blender/gpu/GPU_buffers.h b/source/blender/gpu/GPU_buffers.h
index a8656c05224..ee7abe08aba 100644
--- a/source/blender/gpu/GPU_buffers.h
+++ b/source/blender/gpu/GPU_buffers.h
@@ -147,6 +147,7 @@ typedef struct GPUVertPointLink {
 /* used for GLSL materials */
 typedef struct GPUAttrib {
 	int index;
+	int info_index;
 	int size;
 	int type;
 } GPUAttrib;
@@ -179,6 +180,10 @@ typedef enum {
 	GPU_BINDING_INDEX = 1,
 } GPUBindingType;
 
+typedef enum {
+	GPU_ATTR_INFO_SRGB = (1 << 0),
+} GPUAttrInfo;
+
 /* called before drawing */
 void GPU_vertex_setup(struct DerivedMesh *dm);
 void GPU_normal_setup(struct DerivedMesh *dm);
diff --git a/source/blender/gpu/GPU_shader.h b/source/blender/gpu/GPU_shader.h
index 4c674b460aa..762329ee077 100644
--- a/source/blender/gpu/GPU_shader.h
+++ b/source/blender/gpu/GPU_shader.h
@@ -104,6 +104,7 @@ typedef struct GPUVertexAttribs {
 	struct {
 		int type;
 		int glindex;
+		int glinfoindoex;
 		int gltexco;
 		int attribid;
 		char name[64];	/* MAX_CUSTOMDATA_LAYER_NAME */
diff --git a/source/blender/gpu/intern/gpu_buffers.c b/source/blender/gpu/intern/gpu_buffers.c
index 09d0a383426..f80ce3c1fab 100644
--- a/source/blender/gpu/intern/gpu_buffers.c
+++ b/source/blender/gpu/intern/gpu_buffers.c
@@ -822,6 +822,12 @@ void GPU_interleaved_attrib_setup(GPUBuffer *buffer, GPUAttrib data[], int numda
 	
 	for (i = 0; i < numdata; i++) {
 		glEnableVertexAttribArray(data[i].index);
+		int info = 0;
+		if (data[i].type == GL_UNSIGNED_BYTE) {
+			info |= GPU_ATTR_INFO_SRGB;
+		}
+		glUniform1i(data[i].info_index, info);
+
 		glVertexAttribPointer(data[i].index, data[i].size, data[i].type,
 		                         GL_TRUE, elementsize, BUFFER_OFFSET(offset));
 		offset += data[i].size * GPU_typesize(data[i].type);
diff --git a/source/blender/gpu/intern/gpu_codegen.c b/source/blender/gpu/intern/gpu_codegen.c
index 94d52c3617c..58ef4063430 100644
--- a/source/blender/gpu/intern/gpu_codegen.c
+++ b/source/blender/gpu/intern/gpu_codegen.c
@@ -749,6 +749,7 @@ static char *code_generate_vertex(ListBase *nodes, const GPUMatType type)
 				BLI_dynstr_appendf(ds, "%s %s att%d;\n",
 					GLEW_VERSION_3_0 ? "in" : "attribute",
 					GPU_DATATYPE_STR[input->type], input->attribid);
+				BLI_dynstr_appendf(ds, "uniform int att%d_info;\n",  input->attribid);
 				BLI_dynstr_appendf(ds, "%s %s var%d;\n",
 					GLEW_VERSION_3_0 ? "out" : "varying",
 					GPU_DATATYPE_STR[input->type], input->attribid);
@@ -801,7 +802,8 @@ static char *code_generate_vertex(ListBase *nodes, const GPUMatType type)
 						BLI_dynstr_appendf(ds, "#ifndef USE_OPENSUBDIV\n");
 					}
 #endif
-					BLI_dynstr_appendf(ds, "\tvar%d = att%d;\n", input->attribid, input->attribid);
+					BLI_dynstr_appendf(ds, "\tset_var_from_attr(att%d, att%d_info, var%d);\n",
+					                   input->attribid, input->attribid, input->attribid);
 #ifdef WITH_OPENSUBDIV
 					if (is_mtface) {
 						BLI_dynstr_appendf(ds, "#endif\n");
diff --git a/source/blender/gpu/intern/gpu_material.c b/source/blender/gpu/intern/gpu_material.c
index aaa52b2c3f6..99ecf687f70 100644
--- a/source/blender/gpu/intern/gpu_material.c
+++ b/source/blender/gpu/intern/gpu_material.c
@@ -212,6 +212,9 @@ static void gpu_material_set_attrib_id(GPUMaterial *material)
 		BLI_snprintf(name, sizeof(name), "att%d", attribs->layer[a].attribid);
 		attribs->layer[a].glindex = GPU_shader_get_attribute(shader, name);
 
+		BLI_snprintf(name, sizeof(name), "att%d_info", attribs->layer[a].attribid);
+		attribs->layer[a].glinfoindoex = GPU_shader_get_uniform(shader, name);
+
 		if (attribs->layer[a].glindex >= 0) {
 			attribs->layer[b] = attribs->layer[a];
 			b++;
diff --git a/source/blender/gpu/shaders/gpu_shader_material.glsl b/source/blender/gpu/shaders/gpu_shader_material.glsl
index dae66ce7eb5..9914c4bb362 100644
--- a/source/blender/gpu/shaders/gpu_shader_material.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_material.glsl
@@ -2668,9 +2668,6 @@ void node_gamma(vec4 col, float gamma, out vec4 outcol)
 
 void node_attribute(vec3 attr, out vec4 outcol, out vec3 outvec, out float outf)
 {
-	/* TODO(sergey): This needs linearization for vertex color.
-	 * But how to detect cases when input is linear and when it's srgb?
-	 */
 	outcol = vec4(attr, 1.0);
 	outvec = attr;
 	outf = (attr.x + attr.y + attr.z) / 3.0;
diff --git a/source/blender/gpu/shaders/gpu_shader_vertex.glsl b/source/blender/gpu/shaders/gpu_shader_vertex.glsl
index 5824d5a80db..a91d9e3e6f2 100644
--- a/source/blender/gpu/shaders/gpu_shader_vertex.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_vertex.glsl
@@ -14,6 +14,58 @@ varying vec3 varnormal;
 varying float gl_ClipDistance[6];
 #endif
 
+float srgb_to_linearrgb(float c)
+{
+	if (c < 0.04045)
+		return (c < 0.0) ? 0.0 : c * (1.0 / 12.92);
+	else
+		return pow((c + 0.055) * (1.0 / 1.055), 2.4);
+}
+
+void srgb_to_linearrgb(vec3 col_from, out vec3 col_to)
+{
+	col_to.r = srgb_to_linearrgb(col_from.r);
+	col_to.g = srgb_to_linearrgb(col_from.g);
+	col_to.b = srgb_to_linearrgb(col_from.b);
+}
+
+void srgb_to_linearrgb(vec4 col_from, out vec4 col_to)
+{
+	col_to.r = srgb_to_linearrgb(col_from.r);
+	col_to.g = srgb_to_linearrgb(col_from.g);
+	col_to.b = srgb_to_linearrgb(col_from.b);
+	col_to.a = col_from.a;
+}
+
+bool is_srgb(int info)
+{
+#ifdef USE_NEW_SHADING
+	return (info == 1)? true: false;
+#else
+	return false;
+#endif
+}
+
+void set_var_from_attr(vec3 attr, int info, out vec3 var)
+{
+	if (is_srgb(info)) {
+		srgb_to_linearrgb(attr, var);
+	}
+	else {
+		var = attr;
+	}
+}
+
+void set_var_from_attr(vec4 attr, int info, out vec4 var)
+{
+	if (is_srgb(info)) {
+		srgb_to_linearrgb(attr, var);
+	}
+	else {
+		var = attr;
+	}
+}
+
 void main()
 {
 #ifndef USE_OPENSUBDIV