output-layer: add support for scaling buffers

This allows callers to set a destination size different from the
buffer size to scale them.

The DRM backend supports this. The Wayland backend doesn't yet
(we'd need to wire up viewporter).

backend/drm/libliftoff.c

@@ -196,10 +196,10 @@ static bool set_layer_props(struct wlr_drm_backend *drm,
 		return false;
 	}
 
-	uint64_t crtc_x = (uint64_t)state->x;
-	uint64_t crtc_y = (uint64_t)state->y;
-	uint64_t crtc_w = (uint64_t)width;
-	uint64_t crtc_h = (uint64_t)height;
+	uint64_t crtc_x = (uint64_t)state->dst_box.x;
+	uint64_t crtc_y = (uint64_t)state->dst_box.y;
+	uint64_t crtc_w = (uint64_t)state->dst_box.width;
+	uint64_t crtc_h = (uint64_t)state->dst_box.height;
 
 	uint64_t src_x = to_fp16(0);
 	uint64_t src_y = to_fp16(0);

backend/wayland/output.c

@@ -283,9 +283,15 @@ static bool output_test(struct wlr_output *wlr_output,
 		for (ssize_t i = state->layers_len - 1; i >= 0; i--) {
 			struct wlr_output_layer_state *layer_state = &state->layers[i];
 			if (layer_state->buffer != NULL) {
-				if (layer_state->x < 0 || layer_state->y < 0 ||
-						layer_state->x + layer_state->buffer->width > wlr_output->width ||
-						layer_state->y + layer_state->buffer->height > wlr_output->height) {
+				int x = layer_state->dst_box.x;
+				int y = layer_state->dst_box.y;
+				int width = layer_state->dst_box.width;
+				int height = layer_state->dst_box.height;
+				if (x < 0 || y < 0 ||
+						x + width > wlr_output->width ||
+						y + height > wlr_output->height ||
+						width != layer_state->buffer->width ||
+						height != layer_state->dst_box.height) {
 					supported = false;
 				}
 				supported = supported &&
@@ -376,8 +382,9 @@ static void output_layer_unmap(struct wlr_wl_output_layer *layer) {
 static bool output_layer_commit(struct wlr_wl_output *output,
 		struct wlr_wl_output_layer *layer,
 		const struct wlr_output_layer_state *state) {
-	if (state->layer->x != state->x || state->layer->y != state->y) {
-		wl_subsurface_set_position(layer->subsurface, state->x, state->y);
+	if (state->layer->dst_box.x != state->dst_box.x ||
+			state->layer->dst_box.y != state->dst_box.y) {
+		wl_subsurface_set_position(layer->subsurface, state->dst_box.x, state->dst_box.y);
 	}
 
 	if (state->buffer == NULL) {

examples/output-layers.c

@@ -74,8 +74,12 @@ static void output_handle_frame(struct wl_listener *listener, void *data) {
 		*layer_state = (struct wlr_output_layer_state){
 			.layer = output_surface->layer,
 			.buffer = output_surface->buffer,
-			.x = output_surface->x,
-			.y = output_surface->y,
+			.dst_box = {
+				.x = output_surface->x,
+				.y = output_surface->y,
+				.width = output_surface->wlr_surface->current.width,
+				.height = output_surface->wlr_surface->current.height,
+			},
 		};
 	}
 

include/wlr/types/wlr_output_layer.h

@@ -11,6 +11,7 @@
 
 #include <wlr/render/drm_format_set.h>
 #include <wlr/types/wlr_output.h>
+#include <wlr/util/box.h>
 #include <wlr/util/addon.h>
 
 /**
@@ -51,7 +52,7 @@ struct wlr_output_layer {
 
 	// private state
 
-	int x, y;
+	struct wlr_box dst_box;
 };
 
 /**
@@ -62,8 +63,8 @@ struct wlr_output_layer_state {
 
 	// Buffer to display, or NULL to disable the layer
 	struct wlr_buffer *buffer;
-	// Position in output-buffer-local coordinates
-	int x, y;
+	// Destination box in output-buffer-local coordinates
+	struct wlr_box dst_box;
 
 	// Populated by the backend after wlr_output_test() and wlr_output_commit(),
 	// indicates whether the backend has acknowledged and will take care of

types/output/output.c

@@ -851,8 +851,7 @@ bool wlr_output_commit_state(struct wlr_output *output,
 			wl_list_insert(output->layers.prev, &layer->link);
 
 			// Commit layer state
-			layer->x = layer_state->x;
-			layer->y = layer_state->y;
+			layer->dst_box = layer_state->dst_box;
 		}
 	}