When using an X server-side font with Cairo rendering, PuTTY takes the
rather horrible approach of rendering each glyph it uses into a depth-1
Pixmap and then copying the result into a Cairo surface that it uses
every time it wants to display that glyph.
Heretofore, the conversion of the Pixmap into a Cairo surface was done
by downloading it using XGetImage() and then manually re-arringing the
bits into a suitable form for Cairo. But Cairo has a way of turning an
X Drawable (including a Pixmap) into a surface, and then it's just a
case of copying one surface to another using cairo_paint(). So that's
what PuTTY does now and the process is a little less unpleasant than it
was.
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