weston_buffer: Add type field

Rather than open-coding various resource -> type accessors, just stick a
type enum in the buffer struct.

Signed-off-by: Daniel Stone <daniels@collabora.com>

include/libweston/libweston.h

@@ -1177,10 +1177,18 @@ struct weston_buffer {
 	struct wl_signal destroy_signal;
 	struct wl_listener destroy_listener;
 
+	enum {
+		WESTON_BUFFER_SHM,
+		WESTON_BUFFER_DMABUF,
+		WESTON_BUFFER_RENDERER_OPAQUE,
+	} type;
+
 	union {
 		struct wl_shm_buffer *shm_buffer;
+		void *dmabuf;
 		void *legacy_buffer;
 	};
+
 	int32_t width, height;
 	uint32_t busy_count;
 	int y_inverted;

libweston/compositor.c

@@ -2410,11 +2410,14 @@ weston_buffer_from_resource(struct weston_compositor *ec,
 	wl_resource_add_destroy_listener(resource, &buffer->destroy_listener);
 
 	if ((shm = wl_shm_buffer_get(buffer->resource))) {
+		buffer->type = WESTON_BUFFER_SHM;
 		buffer->shm_buffer = shm;
 		buffer->width = wl_shm_buffer_get_width(shm);
 		buffer->height = wl_shm_buffer_get_height(shm);
 		buffer->y_inverted = true;
 	} else if ((dmabuf = linux_dmabuf_buffer_get(buffer->resource))) {
+		buffer->type = WESTON_BUFFER_DMABUF;
+		buffer->dmabuf = dmabuf;
 		buffer->width = dmabuf->attributes.width;
 		buffer->height = dmabuf->attributes.height;
 		buffer->y_inverted =
@@ -2425,6 +2428,7 @@ weston_buffer_from_resource(struct weston_compositor *ec,
 		    !ec->renderer->fill_buffer_info(ec, buffer)) {
 			goto fail;
 		}
+		buffer->type = WESTON_BUFFER_RENDERER_OPAQUE;
 	}
 
 	return buffer;