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Improve accuracy of destination coordinates in generic StretchBlit() implementation

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It's not possible to map the scaled integer coordinates to the exact
destination location. The inaccuracy can be (mostly) avoided by shifting
the DC origin instead. Also fixes handling of non-zero logical origin.

See #18129
This commit is contained in:
Paul Cornett
2018-05-05 11:45:54 -07:00
parent 2e8516c5fe
commit 41a920cf72
1 changed files with 21 additions and 2 deletions
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23
src/common/dcbase.cpp
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@@ -581,15 +581,34 @@ wxDCImpl::DoStretchBlit(wxCoord xdest, wxCoord ydest,
double xscale = (double)srcWidth/dstWidth,
yscale = (double)srcHeight/dstHeight;
// Shift origin to avoid imprecision of integer destination coordinates
const int deviceOriginX = m_deviceOriginX;
const int deviceOriginY = m_deviceOriginY;
const int deviceLocalOriginX = m_deviceLocalOriginX;
const int deviceLocalOriginY = m_deviceLocalOriginY;
const int logicalOriginX = m_logicalOriginX;
const int logicalOriginY = m_logicalOriginY;
m_deviceOriginX = LogicalToDeviceX(xdest);
m_deviceOriginY = LogicalToDeviceY(ydest);
m_deviceLocalOriginX = 0;
m_deviceLocalOriginY = 0;
m_logicalOriginX = 0;
m_logicalOriginY = 0;
double xscaleOld, yscaleOld;
GetUserScale(&xscaleOld, &yscaleOld);
SetUserScale(xscaleOld/xscale, yscaleOld/yscale);
bool rc = DoBlit(wxCoord(xdest*xscale), wxCoord(ydest*yscale),
wxCoord(dstWidth*xscale), wxCoord(dstHeight*yscale),
bool rc = DoBlit(0, 0, srcWidth, srcHeight,
source,
xsrc, ysrc, rop, useMask, xsrcMask, ysrcMask);
m_deviceOriginX = deviceOriginX;
m_deviceOriginY = deviceOriginY;
m_deviceLocalOriginX = deviceLocalOriginX;
m_deviceLocalOriginY = deviceLocalOriginY;
m_logicalOriginX = logicalOriginX;
m_logicalOriginY = logicalOriginY;
SetUserScale(xscaleOld, yscaleOld);
return rc;