Support 10-bit screenshots by downsampling to 8-bit

This commit introduces support for all eight 10-bit colour formats
supported by wl_shm.

le32toh is used to convert little endian pixels to host endianness.
This function is available on Linux in <endian.h> and FreeBSD in
<sys/endian.h>.

background-image.c

@@ -1,9 +1,16 @@
+#define _DEFAULT_SOURCE
 #include <assert.h>
 #include "background-image.h"
 #include "cairo.h"
 #include "log.h"
 #include "swaylock.h"
 
+#ifdef __FreeBSD__
+#	include <sys/endian.h>
+#else
+#	include <endian.h>
+#endif
+
 // Cairo RGB24 uses 32 bits per pixel, as XRGB, in native endianness.
 // xrgb32_le uses 32 bits per pixel, as XRGB, little endian (BGRX big endian).
 void cairo_rgb24_from_xrgb32_le(unsigned char *buf, int width, int height, int stride) {
@@ -32,6 +39,58 @@ void cairo_rgb24_from_xbgr32_le(unsigned char *buf, int width, int height, int s
 	}
 }
 
+void cairo_rgb24_from_xrgb2101010_le(unsigned char *buf, int width, int height, int stride) {
+	for (int y = 0; y < height; ++y) {
+		for (int x = 0; x < width; ++x) {
+			uint32_t *pix = (uint32_t *) (buf + y * stride + x * 4);
+			uint32_t color = le32toh(*pix);
+			*pix = 0 |
+				((color >> 22) & 0xFF) << 16 |
+				((color >> 12) & 0xFF) << 8 |
+				((color >> 2) & 0xFF);
+		}
+	}
+}
+
+void cairo_rgb24_from_xbgr2101010_le(unsigned char *buf, int width, int height, int stride) {
+	for (int y = 0; y < height; ++y) {
+		for (int x = 0; x < width; ++x) {
+			uint32_t *pix = (uint32_t *) (buf + y * stride + x * 4);
+			uint32_t color = le32toh(*pix);
+			*pix = 0 |
+				((color >> 2) & 0xFF) << 16 |
+				((color >> 12) & 0xFF) << 8 |
+				((color >> 22) & 0xFF);
+		}
+	}
+}
+
+void cairo_rgb24_from_rgbx1010102_le(unsigned char *buf, int width, int height, int stride) {
+	for (int y = 0; y < height; ++y) {
+		for (int x = 0; x < width; ++x) {
+			uint32_t *pix = (uint32_t *) (buf + y * stride + x * 4);
+			uint32_t color = le32toh(*pix);
+			*pix = 0 |
+				((color >> 24) & 0xFF) << 16 |
+				((color >> 14) & 0xFF) << 8 |
+				((color >> 4) & 0xFF);
+		}
+	}
+}
+
+void cairo_rgb24_from_bgrx1010102_le(unsigned char *buf, int width, int height, int stride) {
+	for (int y = 0; y < height; ++y) {
+		for (int x = 0; x < width; ++x) {
+			uint32_t *pix = (uint32_t *) (buf + y * stride + x * 4);
+			uint32_t color = le32toh(*pix);
+			*pix = 0 |
+				((color >> 4) & 0xFF) << 16 |
+				((color >> 14) & 0xFF) << 8 |
+				((color >> 24) & 0xFF);
+		}
+	}
+}
+
 enum background_mode parse_background_mode(const char *mode) {
 	if (strcmp(mode, "stretch") == 0) {
 		return BACKGROUND_MODE_STRETCH;
@@ -169,6 +228,30 @@ cairo_surface_t *load_background_from_buffer(void *buf, uint32_t format,
 				cairo_image_surface_get_width(image),
 				cairo_image_surface_get_height(image),
 				cairo_image_surface_get_stride(image));
+	} else if (format == WL_SHM_FORMAT_XRGB2101010 || format == WL_SHM_FORMAT_ARGB2101010) {
+		cairo_rgb24_from_xrgb2101010_le(
+				cairo_image_surface_get_data(image),
+				cairo_image_surface_get_width(image),
+				cairo_image_surface_get_height(image),
+				cairo_image_surface_get_stride(image));
+	} else if (format == WL_SHM_FORMAT_XBGR2101010 || format == WL_SHM_FORMAT_ABGR2101010) {
+		cairo_rgb24_from_xbgr2101010_le(
+				cairo_image_surface_get_data(image),
+				cairo_image_surface_get_width(image),
+				cairo_image_surface_get_height(image),
+				cairo_image_surface_get_stride(image));
+	} else if (format == WL_SHM_FORMAT_RGBX1010102 || format == WL_SHM_FORMAT_RGBA1010102) {
+		cairo_rgb24_from_rgbx1010102_le(
+				cairo_image_surface_get_data(image),
+				cairo_image_surface_get_width(image),
+				cairo_image_surface_get_height(image),
+				cairo_image_surface_get_stride(image));
+	} else if (format == WL_SHM_FORMAT_BGRX1010102 || format == WL_SHM_FORMAT_BGRA1010102) {
+		cairo_rgb24_from_bgrx1010102_le(
+				cairo_image_surface_get_data(image),
+				cairo_image_surface_get_width(image),
+				cairo_image_surface_get_height(image),
+				cairo_image_surface_get_stride(image));
 	} else {
 		if (format != WL_SHM_FORMAT_XRGB8888 && format != WL_SHM_FORMAT_ARGB8888) {
 			swaylock_log(LOG_ERROR,