Add wlr_box to crop buffer for DRM output

backend/drm/atomic.c

@@ -131,7 +131,7 @@ static void plane_disable(struct atomic *atom, struct wlr_drm_plane *plane) {
 	atomic_add(atom, id, props->crtc_id, 0);
 }
 
-static void set_plane_props(struct atomic *atom, struct wlr_drm_backend *drm,
+static void set_plane_props(struct atomic *atom, struct wlr_box source_box,
 		struct wlr_drm_plane *plane, uint32_t crtc_id, int32_t x, int32_t y) {
 	uint32_t id = plane->id;
 	const union wlr_drm_plane_props *props = &plane->props;
@@ -141,12 +141,14 @@ static void set_plane_props(struct atomic *atom, struct wlr_drm_backend *drm,
 		goto error;
 	}
 
-	uint32_t width = fb->wlr_buf->width;
+	uint32_t width = source_box.width ? (uint32_t)source_box.width :
-	uint32_t height = fb->wlr_buf->height;
+		fb->wlr_buf->width;
+	uint32_t height = source_box.height ? (uint32_t)source_box.height :
+		fb->wlr_buf->height;
 
 	// The src_* properties are in 16.16 fixed point
-	atomic_add(atom, id, props->src_x, 0);
+	atomic_add(atom, id, props->src_x, (uint64_t)source_box.x << 16);
-	atomic_add(atom, id, props->src_y, 0);
+	atomic_add(atom, id, props->src_y, (uint64_t)source_box.y << 16);
 	atomic_add(atom, id, props->src_w, (uint64_t)width << 16);
 	atomic_add(atom, id, props->src_h, (uint64_t)height << 16);
 	atomic_add(atom, id, props->crtc_w, width);
@@ -239,20 +241,36 @@ static bool atomic_crtc_commit(struct wlr_drm_connector *conn,
 	atomic_add(&atom, crtc->id, crtc->props.mode_id, mode_id);
 	atomic_add(&atom, crtc->id, crtc->props.active, active);
 	if (active) {
+		struct wlr_box source_box;
+		if (state->committed & WLR_OUTPUT_STATE_SOURCE_BOX) {
+			/**
+			 * Grab source box from output in order to crop the
+			 * buffer.
+			 */
+			source_box = state->source_box;
+		}
+		else {
+			// Use dummy source box
+			source_box.x = source_box.y = source_box.width =
+				source_box.height = 0;
+		}
 		if (crtc->props.gamma_lut != 0) {
 			atomic_add(&atom, crtc->id, crtc->props.gamma_lut, gamma_lut);
 		}
 		if (crtc->props.vrr_enabled != 0) {
 			atomic_add(&atom, crtc->id, crtc->props.vrr_enabled, vrr_enabled);
 		}
-		set_plane_props(&atom, drm, crtc->primary, crtc->id, 0, 0);
+		set_plane_props(&atom, source_box, crtc->primary, crtc->id, 0, 0);
 		if (crtc->primary->props.fb_damage_clips != 0) {
 			atomic_add(&atom, crtc->primary->id,
 				crtc->primary->props.fb_damage_clips, fb_damage_clips);
 		}
 		if (crtc->cursor) {
 			if (drm_connector_is_cursor_visible(conn)) {
-				set_plane_props(&atom, drm, crtc->cursor, crtc->id,
+				// Ensure source_box is unset for cursor plane
+				source_box.x = source_box.y = source_box.width =
+					source_box.height = 0;
+				set_plane_props(&atom, source_box, crtc->cursor, crtc->id,
 					conn->cursor_x, conn->cursor_y);
 			} else {
 				plane_disable(&atom, crtc->cursor);

include/wlr/types/wlr_output.h

@@ -16,6 +16,7 @@
 #include <wayland-util.h>
 #include <wlr/types/wlr_buffer.h>
 #include <wlr/util/addon.h>
+#include <wlr/types/wlr_box.h>
 
 struct wlr_output_mode {
 	int32_t width, height;
@@ -72,6 +73,7 @@ enum wlr_output_state_field {
 	WLR_OUTPUT_STATE_TRANSFORM = 1 << 5,
 	WLR_OUTPUT_STATE_ADAPTIVE_SYNC_ENABLED = 1 << 6,
 	WLR_OUTPUT_STATE_GAMMA_LUT = 1 << 7,
+	WLR_OUTPUT_STATE_SOURCE_BOX = 1 << 8,
 };
 
 enum wlr_output_state_mode_type {
@@ -89,6 +91,9 @@ struct wlr_output_state {
 	float scale;
 	enum wl_output_transform transform;
 	bool adaptive_sync_enabled;
+	/* allow partial buffer scanout for tiling displays
+	 * only valid if WLR_OUTPUT_STATE_SOURCE_BOX */
+	struct wlr_box source_box; // source box for respective output
 
 	// only valid if WLR_OUTPUT_STATE_BUFFER
 	struct wlr_buffer *buffer;
@@ -372,6 +377,14 @@ uint32_t wlr_output_preferred_read_format(struct wlr_output *output);
  */
 void wlr_output_set_damage(struct wlr_output *output,
 	pixman_region32_t *damage);
+/**
+ * This can be used in case the output buffer is larger than the buffer that
+ * is supposed to be presented on the actual screen attached to the DRM
+ * connector. Current use case are hi-res tiling displays which use multiple
+ * DRM connectors to make up the full monitor.
+ */
+void wlr_output_set_source_box(struct wlr_output *output,
+	struct wlr_box source_box);
 /**
  * Test whether the pending output state would be accepted by the backend. If
  * this function returns true, `wlr_output_commit` can only fail due to a

types/output/output.c

@@ -714,6 +714,12 @@ void wlr_output_attach_buffer(struct wlr_output *output,
 	output->pending.buffer = wlr_buffer_lock(buffer);
 }
 
+void wlr_output_set_source_box(struct wlr_output *output,
+		struct wlr_box source_box) {
+	output->pending.source_box = source_box;
+	output->pending.committed |= WLR_OUTPUT_STATE_SOURCE_BOX;
+}
+
 void wlr_output_send_frame(struct wlr_output *output) {
 	output->frame_pending = false;
 	if (output->enabled) {