Fix T47207: Material shading incorrectly handles colorramp node

The issue was introduced by a fix for T44713 which only made GLSL
consistent with Cycles.

Now we do have conditional averaging or proper luma weighting based
on whether we're new old old shading system. Not totally ideal but
should work for until we re-design viewport possibly breaking how
Blender Internal does implicit conversion.

source/blender/gpu/GPU_shader.h

@@ -46,6 +46,7 @@ struct GPUTexture;
 enum {
 	GPU_SHADER_FLAGS_NONE = 0,
 	GPU_SHADER_FLAGS_SPECIAL_OPENSUBDIV = (1 << 0),
+	GPU_SHADER_FLAGS_NEW_SHADING        = (1 << 1),
 };
 
 GPUShader *GPU_shader_create(

source/blender/gpu/intern/gpu_codegen.c

@@ -318,7 +318,9 @@ static void codegen_convert_datatype(DynStr *ds, int from, int to, const char *t
 		BLI_dynstr_append(ds, name);
 	}
 	else if (to == GPU_FLOAT) {
-		if (from == GPU_VEC4 || from == GPU_VEC3)
+		if (from == GPU_VEC4)
+			BLI_dynstr_appendf(ds, "convert_rgba_to_float(%s)", name);
+		else if (from == GPU_VEC3)
 			BLI_dynstr_appendf(ds, "(%s.r + %s.g + %s.b) / 3.0", name, name, name);
 		else if (from == GPU_VEC2)
 			BLI_dynstr_appendf(ds, "%s.r", name);
@@ -1641,7 +1643,9 @@ static void gpu_nodes_prune(ListBase *nodes, GPUNodeLink *outlink)
 GPUPass *GPU_generate_pass(
         ListBase *nodes, GPUNodeLink *outlink,
         GPUVertexAttribs *attribs, int *builtins,
-        const GPUMatType type, const char *UNUSED(name), const bool use_opensubdiv)
+        const GPUMatType type, const char *UNUSED(name),
+        const bool use_opensubdiv,
+        const bool use_new_shading)
 {
 	GPUShader *shader;
 	GPUPass *pass;
@@ -1664,6 +1668,14 @@ GPUPass *GPU_generate_pass(
 	fragmentcode = code_generate_fragment(nodes, outlink->output);
 	vertexcode = code_generate_vertex(nodes, type);
 	geometrycode = code_generate_geometry(nodes, use_opensubdiv);
+
+	int flags = GPU_SHADER_FLAGS_NONE;
+	if (use_opensubdiv) {
+		flags |= GPU_SHADER_FLAGS_SPECIAL_OPENSUBDIV;
+	}
+	if (use_new_shading) {
+		flags |= GPU_SHADER_FLAGS_NEW_SHADING;
+	}
 	shader = GPU_shader_create_ex(vertexcode,
 	                              fragmentcode,
 	                              geometrycode,
@@ -1672,8 +1684,7 @@ GPUPass *GPU_generate_pass(
 	                              0,
 	                              0,
 	                              0,
-	                              use_opensubdiv ? GPU_SHADER_FLAGS_SPECIAL_OPENSUBDIV
-	                                             : GPU_SHADER_FLAGS_NONE);
+	                              flags);
 
 	/* failed? */
 	if (!shader) {

source/blender/gpu/intern/gpu_codegen.h

@@ -172,7 +172,9 @@ typedef struct GPUPass GPUPass;
 
 GPUPass *GPU_generate_pass(ListBase *nodes, struct GPUNodeLink *outlink,
                            struct GPUVertexAttribs *attribs, int *builtin,
-                           const GPUMatType type, const char *name, const bool use_opensubdiv);
+                           const GPUMatType type, const char *name,
+                           const bool use_opensubdiv,
+                           const bool use_new_shading);
 
 struct GPUShader *GPU_pass_shader(GPUPass *pass);
 

source/blender/gpu/intern/gpu_material.c

@@ -226,7 +226,9 @@ static int GPU_material_construct_end(GPUMaterial *material, const char *passnam
 		GPUNodeLink *outlink = material->outlink;
 		material->pass = GPU_generate_pass(&material->nodes, outlink,
 			&material->attribs, &material->builtins, material->type,
-			passname, material->is_opensubdiv);
+			passname,
+			material->is_opensubdiv,
+			GPU_material_use_new_shading_nodes(material));
 
 		if (!material->pass)
 			return 0;

source/blender/gpu/intern/gpu_shader.c

@@ -183,7 +183,9 @@ static void gpu_shader_standard_extensions(char defines[MAX_EXT_DEFINE_LENGTH],
 	}
 }
 
-static void gpu_shader_standard_defines(char defines[MAX_DEFINE_LENGTH], bool use_opensubdiv)
+static void gpu_shader_standard_defines(char defines[MAX_DEFINE_LENGTH],
+                                        bool use_opensubdiv,
+                                        bool use_new_shading)
 {
 	/* some useful defines to detect GPU type */
 	if (GPU_type_matches(GPU_DEVICE_ATI, GPU_OS_ANY, GPU_DRIVER_ANY)) {
@@ -222,6 +224,10 @@ static void gpu_shader_standard_defines(char defines[MAX_DEFINE_LENGTH], bool us
 	UNUSED_VARS(use_opensubdiv);
 #endif
 
+	if (use_new_shading) {
+		strcat(defines, "#define USE_NEW_SHADING\n");
+	}
+
 	return;
 }
 
@@ -296,7 +302,9 @@ GPUShader *GPU_shader_create_ex(const char *vertexcode,
 		return NULL;
 	}
 
-	gpu_shader_standard_defines(standard_defines, use_opensubdiv);
+	gpu_shader_standard_defines(standard_defines,
+	                            use_opensubdiv,
+	                            (flags & GPU_SHADER_FLAGS_NEW_SHADING) != 0);
 	gpu_shader_standard_extensions(standard_extensions, geocode != NULL);
 
 	if (vertexcode) {

source/blender/gpu/shaders/gpu_shader_material.glsl

@@ -1,3 +1,13 @@
+/* Converters */
+
+float convert_rgba_to_float(vec4 color)
+{
+#ifdef USE_NEW_SHADING
+	return color.r*0.2126 + color.g*0.7152 + color.b*0.0722;
+#else
+	return (color.r + color.g + color.b) / 3.0;
+#endif
+}
 
 float exp_blender(float f)
 {
@@ -743,7 +753,11 @@ void valtorgb(float fac, sampler2D colormap, out vec4 outcol, out float outalpha
 
 void rgbtobw(vec4 color, out float outval)  
 {
+#ifdef USE_NEW_SHADING
+	outval = color.r*0.2126 + color.g*0.7152 + color.b*0.0722;
+#else
 	outval = color.r*0.35 + color.g*0.45 + color.b*0.2; /* keep these factors in sync with texture.h:RGBTOBW */
+#endif
 }
 
 void invert(float fac, vec4 col, out vec4 outcol)