From: Piotr Brzeziński <piotr@centricular.com>
Date: Thu, 1 Jun 2023 14:21:47 +0000 (+0200)
Subject: pngdec: Fix 16bit RGB images display
X-Git-Tag: 1.22.7~242
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=f44a18ee97838b42d65a80f2d4145ed8cc719f0f;p=platform%2Fupstream%2Fgstreamer.git

pngdec: Fix 16bit RGB images display

Due to the alpha value being inserted with _BEFORE, we were ending up
with ARGB instead of RGBA, thus displaying completely wrong colours.
According to libpng's manual, "to add an opaque alpha channel, use filler=0xff
or 0xffff and PNG_FILLER_AFTER which will generate RGBA pixels".

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4759>
---

diff --git a/subprojects/gst-plugins-good/ext/libpng/gstpngdec.c b/subprojects/gst-plugins-good/ext/libpng/gstpngdec.c
index 3775227..dc2043f 100644
--- a/subprojects/gst-plugins-good/ext/libpng/gstpngdec.c
+++ b/subprojects/gst-plugins-good/ext/libpng/gstpngdec.c
@@ -250,7 +250,7 @@ gst_pngdec_caps_create_and_set (GstPngDec * pngdec)
 
   /* Add alpha channel if 16-bit depth, but not for GRAY images */
   if ((bpc > 8) && (color_type != PNG_COLOR_TYPE_GRAY)) {
-    png_set_add_alpha (pngdec->png, 0xffff, PNG_FILLER_BEFORE);
+    png_set_add_alpha (pngdec->png, 0xffff, PNG_FILLER_AFTER);
     png_set_swap (pngdec->png);
   }
 #if 0