Optionally submit 10 bit deep buffers

This requires that the compositor support either XRGB2101010 or XBGR2101010,
and that the background image is a 16-bit PNG.

background-image.c

@@ -22,28 +22,37 @@ enum background_mode parse_background_mode(const char *mode) {
 }
 
 cairo_surface_t *load_background_image(const char *path) {
-	cairo_surface_t *image;
+	cairo_surface_t *image = NULL;
+
 #if HAVE_GDK_PIXBUF
-	GError *err = NULL;
-	GdkPixbuf *pixbuf = gdk_pixbuf_new_from_file(path, &err);
-	if (!pixbuf) {
-		swaybg_log(LOG_ERROR, "Failed to load background image (%s).",
-				err->message);
-		return NULL;
+	// Prefer to load PNG images with Cairo, since it can load images with
+	// higher bit depths at full precision
+	const char *suffix = strrchr(path, '.');
+	if (suffix && (!strcmp(suffix, ".png") || !strcmp(suffix, ".PNG"))) {
+		image = cairo_image_surface_create_from_png(path);
 	}
-	// Correct for embedded image orientation; typical images are not
-	// rotated and will be handled efficiently
-	GdkPixbuf *oriented = gdk_pixbuf_apply_embedded_orientation(pixbuf);
-	g_object_unref(pixbuf);
-	image = gdk_cairo_image_surface_create_from_pixbuf(oriented);
-	g_object_unref(oriented);
-#else
-	image = cairo_image_surface_create_from_png(path);
-#endif // HAVE_GDK_PIXBUF
+
+	// if not a PNG image, try to load with gdk-pixbuf
 	if (!image) {
-		swaybg_log(LOG_ERROR, "Failed to read background image.");
-		return NULL;
+		GError *err = NULL;
+		GdkPixbuf *pixbuf = gdk_pixbuf_new_from_file(path, &err);
+		if (!pixbuf) {
+			swaybg_log(LOG_ERROR, "Failed to load background image (%s).",
+					err->message);
+			return NULL;
+		}
+
+		// Correct for embedded image orientation; typical images are not
+		// rotated and will be handled efficiently
+		GdkPixbuf *oriented = gdk_pixbuf_apply_embedded_orientation(pixbuf);
+		g_object_unref(pixbuf);
+		image = gdk_cairo_image_surface_create_from_pixbuf(oriented);
+		g_object_unref(oriented);
 	}
+#else // !HAVE_GDK_PIXBUF
+	image = cairo_image_surface_create_from_png(path);
+#endif
+
 	if (cairo_surface_status(image) != CAIRO_STATUS_SUCCESS) {
 		swaybg_log(LOG_ERROR, "Failed to read background image: %s."
 #if !HAVE_GDK_PIXBUF

cairo.c

@@ -1,3 +1,4 @@
+#include <assert.h>
 #include <stdint.h>
 #include <cairo.h>
 #include "cairo_util.h"
@@ -13,6 +14,27 @@ void cairo_set_source_u32(cairo_t *cairo, uint32_t color) {
 			(color >> (0*8) & 0xFF) / 255.0);
 }
 
+void cairo_rgb30_swap_rb(cairo_surface_t *surface) {
+	assert(cairo_image_surface_get_format(surface) == CAIRO_FORMAT_RGB30);
+
+	unsigned char *data = cairo_image_surface_get_data(surface);
+	int w = cairo_image_surface_get_width(surface);
+	int h = cairo_image_surface_get_height(surface);
+	int stride = cairo_image_surface_get_stride(surface);
+	for (int y = 0; y < h; y++) {
+		uint32_t *row = (uint32_t *)(data + stride * y);
+		for (int x = 0; x < w; x++) {
+			uint32_t pix = row[x];
+			// swap blue (0:10) and red (20:30)
+			pix = (pix & 0xc00ffc00) | ((pix & 0x3ff00000) >> 20) |
+				((pix & 0x3ff) << 20);
+			row[x] = pix;
+		}
+	}
+
+	cairo_surface_mark_dirty(surface);
+}
+
 #if HAVE_GDK_PIXBUF
 cairo_surface_t* gdk_cairo_image_surface_create_from_pixbuf(const GdkPixbuf *gdkbuf) {
 	int chan = gdk_pixbuf_get_n_channels(gdkbuf);

include/cairo_util.h

@@ -10,6 +10,8 @@
 
 void cairo_set_source_u32(cairo_t *cairo, uint32_t color);
 
+void cairo_rgb30_swap_rb(cairo_surface_t *surface);
+
 #if HAVE_GDK_PIXBUF
 
 cairo_surface_t* gdk_cairo_image_surface_create_from_pixbuf(

main.c

@@ -53,6 +53,8 @@ struct swaybg_state {
 	struct wl_list outputs;  // struct swaybg_output::link
 	struct wl_list images;   // struct swaybg_image::link
 	bool run_display;
+	bool has_xrgb2101010;
+	bool has_xbgr2101010;
 };
 
 struct swaybg_image {
@@ -117,10 +119,26 @@ static struct wl_buffer *draw_buffer(const struct swaybg_output *output,
 			r32, g32, b32, 0xFFFFFFFF);
 	}
 
+	bool deep_image = false;
+	if (surface) {
+		cairo_format_t fmt = cairo_image_surface_get_format(surface);
+		deep_image = deep_image || fmt == CAIRO_FORMAT_RGB30;
+#if CAIRO_VERSION >= CAIRO_VERSION_ENCODE(1, 17, 2)
+		deep_image = deep_image || fmt == CAIRO_FORMAT_RGB96F;
+		deep_image = deep_image || fmt == CAIRO_FORMAT_RGBA128F;
+#endif
+	}
+
+	uint32_t format = WL_SHM_FORMAT_XRGB8888;
+	if (deep_image && output->state->has_xrgb2101010) {
+		format = WL_SHM_FORMAT_XRGB2101010;
+	} else if (deep_image && output->state->has_xbgr2101010) {
+		format = WL_SHM_FORMAT_XBGR2101010;
+	}
 
 	struct pool_buffer buffer;
 	if (!create_buffer(&buffer, output->state->shm,
-			buffer_width, buffer_height, WL_SHM_FORMAT_XRGB8888)) {
+			buffer_width, buffer_height, format)) {
 		return NULL;
 	}
 
@@ -133,6 +151,10 @@ static struct wl_buffer *draw_buffer(const struct swaybg_output *output,
 			output->config->mode, buffer_width, buffer_height);
 	}
 
+	if (format == WL_SHM_FORMAT_XBGR2101010) {
+		cairo_rgb30_swap_rb(buffer.surface);
+	}
+
 	// return wl_buffer for caller to use and destroy
 	struct wl_buffer *wl_buf = buffer.buffer;
 	buffer.buffer = NULL;
@@ -398,6 +420,21 @@ static const struct wl_output_listener output_listener = {
 	.description = output_description,
 };
 
+
+static void shm_format(void *data, struct wl_shm *wl_shm, uint32_t format) {
+	struct swaybg_state *state = data;
+	if (format == WL_SHM_FORMAT_XBGR2101010) {
+		state->has_xbgr2101010 = true;
+	}
+	if (format == WL_SHM_FORMAT_XRGB2101010) {
+		state->has_xrgb2101010 = true;
+	}
+}
+
+static const struct wl_shm_listener shm_listener = {
+	.format = shm_format,
+};
+
 static void handle_global(void *data, struct wl_registry *registry,
 		uint32_t name, const char *interface, uint32_t version) {
 	struct swaybg_state *state = data;
@@ -406,6 +443,7 @@ static void handle_global(void *data, struct wl_registry *registry,
 			wl_registry_bind(registry, name, &wl_compositor_interface, 4);
 	} else if (strcmp(interface, wl_shm_interface.name) == 0) {
 		state->shm = wl_registry_bind(registry, name, &wl_shm_interface, 1);
+		wl_shm_add_listener(state->shm, &shm_listener, state);
 	} else if (strcmp(interface, wl_output_interface.name) == 0) {
 		struct swaybg_output *output = calloc(1, sizeof(struct swaybg_output));
 		output->state = state;

pool-buffer.c

@@ -36,6 +36,18 @@ static int anonymous_shm_open(void) {
 	return -1;
 }
 
+static uint32_t cairo_format_from_wayland_shm(uint32_t shm) {
+	switch (shm) {
+	case WL_SHM_FORMAT_XRGB8888:
+		return CAIRO_FORMAT_RGB24;
+	case WL_SHM_FORMAT_XBGR2101010:
+	case WL_SHM_FORMAT_XRGB2101010:
+		return CAIRO_FORMAT_RGB30;
+	default:
+		assert(0);
+	}
+}
+
 bool create_buffer(struct pool_buffer *buf, struct wl_shm *shm,
 		int32_t width, int32_t height, uint32_t format) {
 	uint32_t stride = width * 4;
@@ -56,10 +68,11 @@ bool create_buffer(struct pool_buffer *buf, struct wl_shm *shm,
 	wl_shm_pool_destroy(pool);
 	close(fd);
 
+	cairo_format_t cairo_fmt = cairo_format_from_wayland_shm(format);
 	buf->size = size;
 	buf->data = data;
 	buf->surface = cairo_image_surface_create_for_data(data,
-			CAIRO_FORMAT_RGB24, width, height, stride);
+			cairo_fmt, width, height, stride);
 	buf->cairo = cairo_create(buf->surface);
 	return true;
 }