[cairo] problem with cairo_image_surface_create_from_png() and cairo_scale()

[cairobeginner cairobeginner]

Hello everybody,

first please excuse my bad english. Is there any mailinglist or forum that
speaks german? Im also not familiar with mailinglists, i hope i do
everything correctly.

I have a problem with cairo_image_surface_create_from_png() and
cairo_scale():

I'm trying to create something like a console-emulation with GTK and cairo,
that is a black screen with 80 x 50 white characters on it. I need this for
a game that uses ASCII-Characters to represent everything. Actually this
game uses the Windows-API to set the console window to fullscreen, but
Microsoft removed that function in Windows 7 so i switched to GTK and
Cairo. There is a german thread about at
http://www.mikrocontroller.net/topic/246034#new .

To do so i created a PNG with all characters and hacked up some code to
copy parts of it on the screen. As long as i not use cairo_scale() or use
only integer values for scaling this works great (it prints a series of 'x'
while im moving with arrow keys), but when i use a float value for zoomY
there is only garbage on screen. Can anybody tell my what is going wrong?

complete source code is here:
http://www.mikrocontroller.net/attachment/134681/main.c
chars.png is here:
http://www.mikrocontroller.net/attachment/133232/chars.png
when using cairo_scale() with float values a picture of the result is here:
http://www.mikrocontroller.net/attachment/133241/k_se.png

Thank you and have a nice day!

cairobeginner
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