wlr_mirror_v1: adds mirroring of variable source on a single destination output

include/wlr/types/wlr_matrix.h

@@ -43,6 +43,11 @@ void wlr_matrix_rotate(float mat[static 9], float rad);
 void wlr_matrix_transform(float mat[static 9],
 	enum wl_output_transform transform);
 
+/** Writes a transformation matrix which applies the inverse of
+ *  transform to mat, such that  transform × inverse = identity */
+void wlr_matrix_transform_inv(float mat[static 9],
+	enum wl_output_transform transform);
+
 /** Writes a 2D orthographic projection matrix to mat of (width, height) with a
  *  specified wl_output_transform.
  *

include/wlr/types/wlr_mirror_v1.h

@@ -0,0 +1,123 @@
+/*
+ * This an unstable interface of wlroots. No guarantees are made regarding the
+ * future consistency of this API.
+ */
+#ifndef WLR_USE_UNSTABLE
+#error "Add -DWLR_USE_UNSTABLE to enable unstable wlroots features"
+#endif
+
+#ifndef WLR_TYPES_wlr_mirror_v1_V1_H
+#define WLR_TYPES_wlr_mirror_v1_V1_H
+
+#include <wayland-client-protocol.h>
+#include <wayland-server-core.h>
+#include <wlr/util/box.h>
+
+/**
+ * Allows mirroring: rendering some contents of one output (the src) on another
+ * output (the dst). dst is fixed for the duration of the session, src may vary.
+ *
+ * On output_srcs precommit, wlr_mirror_v1::ready is emitted. The compositor may
+ * call wlr_mirror_v1_request_ to request to render a frame on dst.
+ *
+ * Compositor must not render on dst for the duration of the session.
+ *
+ * Multiple sessions may run concurrently and one session may mirror another.
+ *
+ * Session will end:
+ *   disable/destroy of dst or all srcs
+ *   wlr_mirror_v1_request_box called with box outside of src
+ *   wlr_mirror_v1_destroy
+ */
+
+enum wlr_mirror_v1_scale {
+	/**
+	 * src will be stretched to cover dst, distorting if necessary.
+	 */
+	WLR_MIRROR_V1_SCALE_FULL,
+	/**
+	 * src will be stretched to the width or the height of dst, preserving the
+	 * aspect ratio.
+	 */
+	WLR_MIRROR_V1_SCALE_ASPECT,
+	/**
+	 * src will be rendered 1:1 at the center of dst. Content may be lost.
+	 */
+	WLR_MIRROR_V1_SCALE_CENTER,
+};
+
+/**
+ * Immutable over session.
+ */
+struct wlr_mirror_v1_params {
+
+	enum wlr_mirror_v1_scale scale;
+
+	/**
+	 * Render the src cursor on dst.
+	 */
+	bool overlay_cursor;
+
+	/**
+	 * srcs to send wlr_mirror_v1::events::ready
+	 */
+	struct wl_array output_srcs;
+
+	/**
+	 * dst, will have mirror_dst set for the duration of the session.
+	 */
+	struct wlr_output *output_dst;
+};
+
+struct wlr_mirror_v1_state;
+struct wlr_mirror_v1 {
+
+	struct {
+		/**
+		 * Ready to render a frame. Handler should call wlr_mirror_v1_request_
+		 * Emitted at precommit, passes potential src.
+		 */
+		struct wl_signal ready;
+
+		/**
+		 * Mirror session is over.
+		 */
+		struct wl_signal destroy;
+	} events;
+
+	// private state
+	struct wlr_mirror_v1_state *state;
+};
+
+/**
+ * Create a mirror session.
+ *
+ * Compositor must stop rendering on dst immediately after this.
+ */
+struct wlr_mirror_v1 *wlr_mirror_v1_create(struct wlr_mirror_v1_params *params);
+
+/**
+ * Destroy a mirror session.
+ *
+ * Compositor may resume rendering on dst.
+ */
+void wlr_mirror_v1_destroy(struct wlr_mirror_v1 *mirror);
+
+/**
+ * Request a blank frame on dst.
+ *
+ * Should be invoked during the wlr_mirror_v1::events::ready handler.
+ */
+void wlr_mirror_v1_request_blank(struct wlr_mirror_v1 *mirror);
+
+/**
+ * Request a frame to render a box within src on dst. box is in output local
+ * coordinates, with respect to its transformation.
+ *
+ * Should be invoked during the wlr_mirror_v1::events::ready handler.
+ */
+void wlr_mirror_v1_request_box(struct wlr_mirror_v1 *mirror,
+		struct wlr_output *output_src, struct wlr_box box);
+
+#endif
+

include/wlr/types/wlr_output.h

@@ -151,6 +151,9 @@ struct wlr_output {
 	// Commit sequence number. Incremented on each commit, may overflow.
 	uint32_t commit_seq;
 
+	// dst for an active wlr_mirror_v1 session
+	bool mirror_dst;
+
 	struct {
 		// Request to render a frame
 		struct wl_signal frame;