libobs-opengl: Bind index buffers to VAO

To be able to use index buffers, they must also be bound to a vertex
array object along with the vertex buffers.

Ideally, if there are multiple index buffers for a vertex buffer,
separate VAOs should be created for each combination.

libobs-opengl/gl-indexbuffer.c

@@ -104,11 +104,5 @@ enum gs_index_type gs_indexbuffer_get_type(const gs_indexbuffer_t *ib)
 
 void device_load_indexbuffer(gs_device_t *device, gs_indexbuffer_t *ib)
 {
-	if (ib == device->cur_index_buffer)
-		return;
-
 	device->cur_index_buffer = ib;
-
-	if (!gl_bind_buffer(GL_ELEMENT_ARRAY_BUFFER, ib->buffer))
-		blog(LOG_ERROR, "device_load_indexbuffer (GL) failed");
 }

libobs-opengl/gl-subsystem.c

@@ -979,7 +979,7 @@ void device_draw(gs_device_t *device, enum gs_draw_mode draw_mode,
 	if (!program)
 		goto fail;
 
-	load_vb_buffers(program, device->cur_vertex_buffer);
+	load_vb_buffers(program, device->cur_vertex_buffer, ib);
 
 	if (program != device->cur_program && device->cur_program) {
 		glUseProgram(0);

libobs-opengl/gl-subsystem.h

@@ -377,7 +377,7 @@ struct gs_vertex_buffer {
 };
 
 extern bool load_vb_buffers(struct gs_program *program,
-		struct gs_vertex_buffer *vb);
+		struct gs_vertex_buffer *vb, struct gs_index_buffer *ib);
 
 struct gs_index_buffer {
 	GLuint               buffer;

libobs-opengl/gl-vertexbuffer.c

@@ -234,7 +234,8 @@ static bool load_vb_buffer(struct shader_attrib *attrib,
 	return success;
 }
 
-bool load_vb_buffers(struct gs_program *program, struct gs_vertex_buffer *vb)
+bool load_vb_buffers(struct gs_program *program, struct gs_vertex_buffer *vb,
+		struct gs_index_buffer *ib)
 {
 	struct gs_shader *shader = program->vertex_shader;
 	size_t i;
@@ -248,6 +249,9 @@ bool load_vb_buffers(struct gs_program *program, struct gs_vertex_buffer *vb)
 			return false;
 	}
 
+	if (ib && !gl_bind_buffer(GL_ELEMENT_ARRAY_BUFFER, ib->buffer))
+		return false;
+
 	return true;
 }