Revert "jpegdec: only allow conversions from RGB"

This reverts commit 2aa2477208c029b0e1b8232d69f4f99a3bf1d473.
The commit is completely wrong, libjpeg-turbo is perfectly capable
of decoding I420 (YUV) to RGB. The test case provided alongside the
aforementioned commit passes without this revert because it decodes
image of JCS_YCrCb color space, so the new `if (clrspc == JCS_RGB)`
condition is false on that image, and the libjpeg-turbo decoding
does not get used. The real bug is hidden by that commit.

The real problem is in the call order of gst_jpeg_dec_prepare_decode()
and gst_jpeg_dec_negotiate(). The gst_jpeg_dec_prepare_decode() calls
jpeg_start_decompress() which sets up internal state of the libjpeg,
however, neither cinfo.out_color_space nor cinfo.raw_data_out are
set correctly yet. Those two are set up in gst_jpeg_dec_negotiate()
which is called a bit later. Therefore, the real fix is the set up
cinfo.out_color_space and cinfo.raw_data_out before calling
jpeg_start_decompress(). This is however a separate patch.

Fixes: 2aa2477208 ("jpegdec: only allow conversions from RGB")
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1687>

diff --git a/subprojects/gst-plugins-good/ext/jpeg/gstjpegdec.c b/subprojects/gst-plugins-good/ext/jpeg/gstjpegdec.c
index 3b66e26..db81b41 100644 (file)
--- a/subprojects/gst-plugins-good/ext/jpeg/gstjpegdec.c
+++ b/subprojects/gst-plugins-good/ext/jpeg/gstjpegdec.c
@@ -1071,9 +1071,8 @@ gst_jpeg_dec_negotiate (GstJpegDec * dec, gint width, gint height, gint clrspc,
     peerformat = gst_structure_get_string (peerstruct, "format");
     peerfmt = gst_video_format_from_string (peerformat);
 
-    /* libjpeg-turbo only supports some colorspace conversions, see
-     * https://raw.githubusercontent.com/libjpeg-turbo/libjpeg-turbo/main/libjpeg.txt */
     switch (peerfmt) {
+      case GST_VIDEO_FORMAT_RGB:
       case GST_VIDEO_FORMAT_RGBx:
       case GST_VIDEO_FORMAT_xRGB:
       case GST_VIDEO_FORMAT_RGBA:
@@ -1083,14 +1082,11 @@ gst_jpeg_dec_negotiate (GstJpegDec * dec, gint width, gint height, gint clrspc,
       case GST_VIDEO_FORMAT_xBGR:
       case GST_VIDEO_FORMAT_BGRA:
       case GST_VIDEO_FORMAT_ABGR:
-        if (clrspc == JCS_RGB) {
-          /* RGB -> other RGB formats */
-          format = peerfmt;
-          dec->format_convert = TRUE;
-          dec->libjpeg_ext_format = gst_fmt_to_jpeg_turbo_ext_fmt (peerfmt);
-        }
+        clrspc = JCS_RGB;
+        format = peerfmt;
+        dec->format_convert = TRUE;
+        dec->libjpeg_ext_format = gst_fmt_to_jpeg_turbo_ext_fmt (peerfmt);
         break;
-        /* TODO: implement conversion from/to other supported colorspaces */
       default:
         break;
     }