(no subject)

Ok. I've done a bit more research on this. As far as I can see there appear to
be two problems.

1, When the zoom is changed GR_Graphics doesn't reload the device font.
        Thus, in a piece of code like this...

        GR_Painter painter(gc);
        gc->setZoomPercentage(100);
        gc->setFont("Times New Roman"... "12pt");
        gc->setZoomPercentage(200);
        printf("%d\n", measureUnremappedChar('A');
        painter.drawChars("A");

        measureUnremappedChar() will be returning the width in pixels for a zoom
        of 200%, but drawChars() will only be drawing at 100%. Thus, the width
        measurement will seem twice as large as it should be.

2, The values returned from the freetype library in
        XAP_UnixFontHandle::measureUnremappedCharForCache() for
        pFace->glyph->linearHoriAdvance don't seemed quite accurate.
        For example, for Arial at 15pt and 100% zoom the width of an "A" is 11
        pixels, but linearHoriAdvance returns 10.004... points. [0]
        Similarly, an "A" in Comic Times MS is 12 pixels wide but
        linearHoriAdvance returns 10.97...pt. Adding 1 and rounding to the
        nearest interger "fixes" the problem for 100% zoom. However, the values
        when the zoom is 200% seem correct.

[0] The device resolution appears to be fixed at 72dpi so in this case
pixels=points.

1, is responsible for the majority of the error observed in the image I posted.
It can be fixed adding the following two lines to
GR_Graphics::setZoomPercentage():

void GR_UnixGraphics::setZoomPercentage(UT_uint32 iZoom)
{
  GR_Graphics::setZoomPercentage (iZoom); // chain up
  // Reset the device font for the new zoom.
  if (m_pFont) // <-- This
    m_pXftFontD = m_pFont->getDeviceXftFont(getZoomPercentage()); // <-- This
}

Is this an appropriate fix?

I'm not at all sure about what can be done about 2.

Best wishes,

R.
Received on Wed Aug 17 07:58:11 2005