From cd22a0f520f471e3bd33bc19cf3b2fa772cdb2a8 Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Fri, 12 May 2023 15:43:38 +0100 Subject: ui: Fix pixel colour channel order for PNG screenshots MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When we take a PNG screenshot the ordering of the colour channels in the data is not correct, resulting in the image having weird colouring compared to the actual display. (Specifically, on a little-endian host the blue and red channels are swapped; on big-endian everything is wrong.) This happens because the pixman idea of the pixel data and the libpng idea differ. PIXMAN_a8r8g8b8 defines that pixels are 32-bit values, with A in bits 24-31, R in bits 16-23, G in bits 8-15 and B in bits 0-7. This means that on little-endian systems the bytes in memory are B G R A and on big-endian systems they are A R G B libpng, on the other hand, thinks of pixels as being a series of values for each channel, so its format PNG_COLOR_TYPE_RGB_ALPHA always wants bytes in the order R G B A This isn't the same as the pixman order for either big or little endian hosts. The alpha channel is also unnecessary bulk in the output PNG file, because there is no alpha information in a screenshot. To handle the endianness issue, we already define in ui/qemu-pixman.h various PIXMAN_BE_* and PIXMAN_LE_* values that give consistent byte-order pixel channel formats. So we can use PIXMAN_BE_r8g8b8 and PNG_COLOR_TYPE_RGB, which both have an in-memory byte order of R G B and 3 bytes per pixel. (PPM format screenshots get this right; they already use the PIXMAN_BE_r8g8b8 format.) Cc: qemu-stable@nongnu.org Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1622 Fixes: 9a0a119a382867 ("Added parameter to take screenshot with screendump as PNG") Signed-off-by: Peter Maydell Reviewed-by: Marc-André Lureau Message-id: 20230502135548.2451309-1-peter.maydell@linaro.org --- ui/console.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/ui/console.c b/ui/console.c index 6e8a3cd..e173731 100644 --- a/ui/console.c +++ b/ui/console.c @@ -311,7 +311,7 @@ static bool png_save(int fd, pixman_image_t *image, Error **errp) png_struct *png_ptr; png_info *info_ptr; g_autoptr(pixman_image_t) linebuf = - qemu_pixman_linebuf_create(PIXMAN_a8r8g8b8, width); + qemu_pixman_linebuf_create(PIXMAN_BE_r8g8b8, width); uint8_t *buf = (uint8_t *)pixman_image_get_data(linebuf); FILE *f = fdopen(fd, "wb"); int y; @@ -341,7 +341,7 @@ static bool png_save(int fd, pixman_image_t *image, Error **errp) png_init_io(png_ptr, f); png_set_IHDR(png_ptr, info_ptr, width, height, 8, - PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE, + PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE); png_write_info(png_ptr, info_ptr); -- cgit v1.1