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Correctly populate max color values in server screen format

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Summary:
Compute max color values from color masks, instead of relying on unreliable `bits_per_rgb_value` provided by `xcb_visualtype_t`.

In some cases (e.g. nvidia?) `bits_per_rgb_value` contains wrong value. This results in wrong max color values, and causes weird color translation inside libvncserver. Clients will see a screen which is sorta recognizable but in a complete off-color, making krfb unusable.

This is probably a bug in drivers, but x11vnc does not use this value[1], so I guess it's fair to ignore it in krfb too.

[1]: https://github.com/LibVNC/x11vnc/blob/master/src/screen.c#L3442

Reviewers: alexeymin, aacid, #kde_applications

Differential Revision: https://phabricator.kde.org/D25876
This commit is contained in:
Albert Astals Cid
2020-01-05 19:10:52 +01:00
parent 6c78a2f98d
commit bb59ce2776
1 changed files with 10 additions and 9 deletions
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19
framebuffers/xcb/xcb_framebuffer.cpp
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@@ -381,49 +381,50 @@ void XCBFrameBuffer::getServerFormat(rfbPixelFormat &format) {
// information about pixels layout
if (root_visualtype) {
uint16_t pixelmaxValue = (1 << root_visualtype->bits_per_rgb_value) - 1;
#ifdef _DEBUG
qDebug("xcb framebuffer: Got info about root visual:\n"
" bits per rgb value: %d\n"
" red mask: %08x\n"
" green mask: %08x\n"
" blue mask: %08x\n"
" pixelMaxValue = %d\n",
" blue mask: %08x\n",
(int)root_visualtype->bits_per_rgb_value,
root_visualtype->red_mask,
root_visualtype->green_mask,
root_visualtype->blue_mask,
(int)pixelmaxValue);
root_visualtype->blue_mask);
#endif
// calculate shifts
format.redShift = 0;
format.redMax = pixelmaxValue;
if (root_visualtype->red_mask) {
while (!(root_visualtype->red_mask & (1 << format.redShift))) {
format.redShift++;
}
}
format.greenShift = 0;
format.greenMax = pixelmaxValue;
if (root_visualtype->green_mask) {
while (!(root_visualtype->green_mask & (1 << format.greenShift))) {
format.greenShift++;
}
}
format.blueShift = 0;
format.blueMax = pixelmaxValue;
if (root_visualtype->blue_mask) {
while (!(root_visualtype->blue_mask & (1 << format.blueShift))) {
format.blueShift++;
}
}
// calculate pixel max value.
// NOTE: bits_per_rgb_value is unreliable, thus should be avoided.
format.redMax = root_visualtype->red_mask >> format.redShift;
format.greenMax = root_visualtype->green_mask >> format.greenShift;
format.blueMax = root_visualtype->blue_mask >> format.blueShift;
#ifdef _DEBUG
qDebug() << " Calculated redShift =" << (int)format.redShift;
qDebug() << " Calculated greenShift =" << (int)format.greenShift;
qDebug() << " Calculated blueShift =" << (int)format.blueShift;
qDebug( " Calculated max values: R%d G%d B%d",
format.redMax, format.greenMax, format.blueMax);
#endif
} else {
// some kind of fallback (unlikely code execution will go this way)