add a function to get the correct mesh buffer automatically

Previously we had to add the correct buffer to the
GLBufferToAttribMapping struct. This doesn't work if we want to deal
with entities at a high level. Now we can specify the buffer type as an
enum, and have a helper function get a reference to the corrent mesh
buffer when loading into GL.

src/main.cpp

@@ -62,8 +62,8 @@ loadScene(RenderState* rs)
 	assert(df_pos_attrib && df_uv_attrib);
 
 	GLBufferToAttribMapping default_mappings[2] = {
-		{ "position", df_pos_attrib, texmesh.vertices },
+		{ "position", df_pos_attrib, VERTEX},
-		{ "uvs", df_uv_attrib, texmesh.uvs }
+		{ "uvs", df_uv_attrib, UV }
 	};
 
 	// NOTE: init new render group

src/shader.cpp

@@ -251,6 +251,18 @@ initGLAttribBuffer(gl_buffer* buf, GLenum target, GLVertexAttrib* attrib)
 	buf->name = utilAllocateCStr(attrib->name);
 }
 
+void*
+getMeshData(const mesh& m, const GLBufferToAttribMapping& mapping)
+{
+	switch (mapping.buf_type) {
+		case VERTEX: return m.vertices;
+		case NORMAL: return m.normals;
+		case UV: return m.uvs;
+		case COLOR: return m.colors;
+		default: return nullptr;
+	}
+}
+
 // FIXME: might as well pass in pointer to GLmesh, since that's how we're
 // 	going to use this, can void copying GLmesh twice that way
 GLmesh
@@ -273,11 +285,13 @@ loadGLMesh(const mesh& m,
 		u32 type_size = getGLTypeSize(attrib->data_type);
 		assert(type_size > 0);
 
+		void* mesh_buf_data = getMeshData(m, mappings[i]);
+		assert(mesh_buf_data);
 		initGLAttribBuffer(&buf, GL_ARRAY_BUFFER, attrib);
 		glBindBuffer(buf.target, buf.id);
 		glBufferData(buf.target,
 			m.num_vertices * type_size,
-			mappings[i].mesh_buf,
+			mesh_buf_data,
 			glm.usage);
 		glVertexAttribPointer(attrib->location, attrib->num_components,
 							attrib->component_type, GL_FALSE, 0, 0);

src/shader.h

@@ -106,11 +106,19 @@ struct GLContext
 	GLTexture* textures;
 };
 
+enum MeshBufferType
+{
+	VERTEX,
+	NORMAL,
+	UV,
+	COLOR
+};
+
 struct GLBufferToAttribMapping
 {
 	const char* buf_name;
 	GLVertexAttrib* attrib;
-	void* mesh_buf;
+	MeshBufferType buf_type;
 };
 
 // TODO: rename to GLMesh