weston_buffer: Change y_inverted to explicit origin enum

y_inverted meant that the buffer's origin was (0,0), and non-inverted
meant that the buffer's origin was (0,height). In practice, every buffer
was 'inverted' into our natural co-ordinate space that we use
everywhere.

Switch to using an explicit origin enum to make this more clear.

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

include/libweston/libweston.h

@@ -1191,7 +1191,10 @@ struct weston_buffer {
 
 	int32_t width, height;
 	uint32_t busy_count;
-	int y_inverted;
+	enum {
+		ORIGIN_TOP_LEFT, /* buffer content starts at (0,0) */
+		ORIGIN_BOTTOM_LEFT, /* buffer content starts at (0, height) */
+	} buffer_origin;
 	void *backend_private;
 
 	const struct pixel_format_info *pixel_format;

libweston/compositor.c

@@ -2415,7 +2415,7 @@ weston_buffer_from_resource(struct weston_compositor *ec,
 		buffer->shm_buffer = shm;
 		buffer->width = wl_shm_buffer_get_width(shm);
 		buffer->height = wl_shm_buffer_get_height(shm);
-		buffer->y_inverted = true;
+		buffer->buffer_origin = ORIGIN_TOP_LEFT;
 		/* wl_shm might create a buffer with an unknown format, so check
 		 * and reject */
 		buffer->pixel_format =
@@ -2435,8 +2435,10 @@ weston_buffer_from_resource(struct weston_compositor *ec,
 		 * unknown format */
 		assert(buffer->pixel_format);
 		buffer->format_modifier = dmabuf->attributes.modifier[0];
-		buffer->y_inverted =
-			!(dmabuf->attributes.flags & ZWP_LINUX_BUFFER_PARAMS_V1_FLAGS_Y_INVERT);
+		if (dmabuf->attributes.flags & ZWP_LINUX_BUFFER_PARAMS_V1_FLAGS_Y_INVERT)
+			buffer->buffer_origin = ORIGIN_BOTTOM_LEFT;
+		else
+			buffer->buffer_origin = ORIGIN_TOP_LEFT;
 	} else {
 		/* Only taken for legacy EGL buffers */
 		if (!ec->renderer->fill_buffer_info ||

libweston/renderer-gl/gl-renderer.c

@@ -2160,6 +2160,7 @@ gl_renderer_fill_buffer_info(struct weston_compositor *ec,
 	struct gl_renderer *gr = get_renderer(ec);
 	EGLint format;
 	uint32_t fourcc;
+	EGLint y_inverted;
 	bool ret = true;
 
 	buffer->legacy_buffer = (struct wl_buffer *)buffer->resource;
@@ -2201,9 +2202,12 @@ gl_renderer_fill_buffer_info(struct weston_compositor *ec,
 
 	/* Assume scanout co-ordinate space i.e. (0,0) is top-left
 	 * if the query fails */
-	buffer->y_inverted = true;
-	gr->query_buffer(gr->egl_display, buffer->legacy_buffer,
-			 EGL_WAYLAND_Y_INVERTED_WL, &buffer->y_inverted);
+	ret = gr->query_buffer(gr->egl_display, buffer->legacy_buffer,
+			       EGL_WAYLAND_Y_INVERTED_WL, &y_inverted);
+	if (!ret || y_inverted)
+		buffer->buffer_origin = ORIGIN_TOP_LEFT;
+	else
+		buffer->buffer_origin = ORIGIN_BOTTOM_LEFT;
 
 	return true;
 }
@@ -2281,7 +2285,7 @@ gl_renderer_attach_egl(struct weston_surface *es, struct weston_buffer *buffer,
 	gs->pitch = buffer->width;
 	gs->height = buffer->height;
 	gs->buffer_type = BUFFER_TYPE_EGL;
-	gs->y_inverted = buffer->y_inverted;
+	gs->y_inverted = (buffer->buffer_origin == ORIGIN_TOP_LEFT);
 }
 
 static void
@@ -2873,7 +2877,7 @@ gl_renderer_attach_dmabuf(struct weston_surface *surface,
 	gs->pitch = buffer->width;
 	gs->height = buffer->height;
 	gs->buffer_type = BUFFER_TYPE_EGL;
-	gs->y_inverted = buffer->y_inverted;
+	gs->y_inverted = (buffer->buffer_origin == ORIGIN_TOP_LEFT);
 	gs->direct_display = dmabuf->direct_display;
 	surface->is_opaque = dmabuf_is_opaque(dmabuf);