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Fix GIF image decoding: do not zero transparent pixels

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For the special transparent color index, the decoder would skip
writing anything out (thus leaving the pixels at 0 rgba value).
Although correct for later frames, for the initial frame this would
loose the color information for such pixels (which one otherwise
could have made visible e.g. by converting then image to an
alpha-less image format).

Change-Id: I316cefce8f21797feedebfbf98296ad84eaa4b99
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
(cherry picked from qt/c309d424f45dc0e7b62fbbbabf20dbfe355f48a7)
Reviewed-by: aavit <eirik.aavitsland@digia.com>
This commit is contained in:
aavit 2012-11-07 15:19:20 +01:00 committed by The Qt Project
parent f4a8e940ed
commit d91c1422a9
3 changed files with 15 additions and 9 deletions
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15
src/gui/image/qgifhandler.cpp
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@ -488,7 +488,7 @@ int QGIFFormat::decode(QImage *image, const uchar *buffer, int length,
} else {
if (needfirst) {
firstcode=oldcode=code;
if (!out_of_bounds && image->height() > y && firstcode!=trans_index)
if (!out_of_bounds && image->height() > y && ((frame == 0) || (firstcode != trans_index)))
((QRgb*)FAST_SCAN_LINE(bits, bpl, y))[x] = color(firstcode);
x++;
if (x>=swidth) out_of_bounds = true;
@ -540,17 +540,13 @@ int QGIFFormat::decode(QImage *image, const uchar *buffer, int length,
}
oldcode=incode;
const int h = image->height();
const QRgb *map = lcmap ? localcmap : globalcmap;
QRgb *line = 0;
if (!out_of_bounds && h > y)
line = (QRgb*)FAST_SCAN_LINE(bits, bpl, y);
while (sp>stack) {
const uchar index = *(--sp);
if (!out_of_bounds && h > y && index!=trans_index) {
if (index > ncols)
line[x] = Q_TRANSPARENT;
else
line[x] = map ? map[index] : 0;
if (!out_of_bounds && h > y && ((frame == 0) || (index != trans_index))) {
line[x] = color(index);
}
x++;
if (x>=swidth) out_of_bounds = true;
@ -1031,11 +1027,12 @@ void QGIFFormat::nextY(unsigned char *bits, int bpl)
inline QRgb QGIFFormat::color(uchar index) const
{
if (index == trans_index || index > ncols)
if (index > ncols)
return Q_TRANSPARENT;
QRgb *map = lcmap ? localcmap : globalcmap;
return map ? map[index] : 0;
QRgb col = map ? map[index] : 0;
return index == trans_index ? col & Q_TRANSPARENT : col;
}
//-------------------------------------------------------------------------

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tests/auto/gui/image/qimagereader/images/trans.gif Normal file
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9
tests/auto/gui/image/qimagereader/tst_qimagereader.cpp
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@ -756,6 +756,15 @@ void tst_QImageReader::gifHandlerBugs()
QVERIFY(io.canRead());
QCOMPARE(io.loopCount(), -1);
}
// Check that pixels with the transparent color are transparent but not zeroed
{
QImageReader io(prefix + "trans.gif");
QVERIFY(io.canRead());
QImage im = io.read();
QCOMPARE(im.pixel(0,0), qRgba(0x3f, 0xff, 0x7f, 0x00));
QCOMPARE(im.pixel(10,10), qRgba(0x3f, 0xff, 0x7f, 0x00));
}
}
void tst_QImageReader::animatedGif()