Change how surface matricies are calculated

examples/compositor/main.c

@@ -8,6 +8,7 @@
 #include <wlr/backend.h>
 #include <wlr/backend/session.h>
 #include <wlr/render.h>
+#include <wlr/render/matrix.h>
 #include <wlr/render/gles2.h>
 #include <wlr/types/wlr_output.h>
 #include <wlr/types/wlr_surface.h>
@@ -41,12 +42,14 @@ void handle_output_frame(struct output_state *output, struct timespec *ts) {
 
 	struct wl_resource *_res;
 	float matrix[16];
+	float transform[16];
 	wl_list_for_each(_res, &sample->compositor.surfaces, link) {
 		struct wlr_surface *surface = wl_resource_get_user_data(_res);
 		wlr_surface_flush_damage(surface);
 		if (surface->texture->valid) {
+			wlr_matrix_translate(&transform, 200, 200, 0);
 			wlr_surface_get_matrix(surface, &matrix,
-				&wlr_output->transform_matrix, 200, 200);
+				&wlr_output->transform_matrix, &transform);
 			wlr_render_with_matrix(sample->renderer, surface->texture, &matrix);
 
 			struct wlr_frame_callback *cb, *cnext;

include/wlr/types/wlr_surface.h

@@ -55,7 +55,17 @@ struct wlr_renderer;
 struct wlr_surface *wlr_surface_create(struct wl_resource *res,
 		struct wlr_renderer *renderer);
 void wlr_surface_flush_damage(struct wlr_surface *surface);
-void wlr_surface_get_matrix(struct wlr_surface *surface, float (*matrix)[16],
-		const float (*projection)[16], int x, int y);
+/**
+ * Gets a matrix you can pass into wlr_render_with_matrix to display this
+ * surface. `matrix` is the output matrix, `projection` is the wlr_output
+ * projection matrix, and `transform` is any additional transformations you want
+ * to perform on the surface (or NULL/the identity matrix if you don't).
+ * `transform` is used before the surface is scaled, so its geometry extends
+ * from 0 to 1 in both dimensions.
+ */
+void wlr_surface_get_matrix(struct wlr_surface *surface,
+		float (*matrix)[16],
+		const float (*projection)[16],
+		const float (*transform)[16]);
 
 #endif

types/wlr_surface.c

@@ -353,14 +353,17 @@ struct wlr_surface *wlr_surface_create(struct wl_resource *res,
 }
 
 void wlr_surface_get_matrix(struct wlr_surface *surface,
-		float (*matrix)[16], const float (*projection)[16], int x, int y) {
+		float (*matrix)[16],
+		const float (*projection)[16],
+		const float (*transform)[16]) {
 	int width = surface->texture->width / surface->current.scale;
 	int height = surface->texture->height / surface->current.scale;
-	float world[16];
+	float scale[16];
 	wlr_matrix_identity(matrix);
-	wlr_matrix_translate(&world, x, y, 0);
-	wlr_matrix_mul(matrix, &world, matrix);
-	wlr_matrix_scale(&world, width, height, 1);
-	wlr_matrix_mul(matrix, &world, matrix);
+	if (transform) {
+		wlr_matrix_mul(matrix, transform, matrix);
+	}
+	wlr_matrix_scale(&scale, width, height, 1);
+	wlr_matrix_mul(matrix, &scale, matrix);
 	wlr_matrix_mul(projection, matrix, matrix);
 }