hi greg
Greg Ewing wrote:
> altern wrote:
>> The example draws a one pixel wide box in the borders of the window.
>> In none of the sytems I tried so far the box was totally visible.
>> There is always one or two sides missing just by one pixel.
>
> What coordinates are you using to draw the box, exactly?
> You might need to offset them by half a pixel so that
> the lines go through the centres of pixels. If you're
> actually trying to draw a line between two pixels,
> different systems may round it in different ways.
This is the way i set the projection and draw the lines, being
size=(800,600) in my example
# the projection
glOrtho(0, size[0], size[1], 0, 1, 0)
# red marquee with diagonal lines cross
glBegin(GL_LINE_LOOP)
glColor3f(1,0,0) #
glVertex2i(0,0)
glVertex2i(size[0], size[1])
glVertex2i(0, size[1])
glVertex2i(size[0], 0)
glVertex2i(0,0) # marquee
glVertex2i(size[0], 0)
glVertex2i(size[0], size[1])
glVertex2i(0, size[1])
glEnd() # end line loop
I tried to replace all the 0 value in all vertexes by 0.5 but it doesnt
work either. I also tried to change the glOrtho to
glOrtho(0.5, size[0], size[1], 0.5, 1, 0)
and also combining both with no luck.
However if I set glOrtho like this
glOrtho(-1, size[0], size[1]+1, 0, 1, 0)
then it works fine on my Debian desktop and on my debian laptop but not
on my laptop with XP. So I decided to do tests in all systems on my
machines. This is the result:
glOrtho(-1, size[0], size[1]+1, 0, 1, 0)
works on Debian desktop with a matrox card
works on Debian laptop with ATI
glOrtho(-1, size[0], size[1]+1, -1, 1, 0)
works on XP laptop with ATI
glOrtho(-1, size[0]+1, size[1], 1, 0)
works on XP Desktop with matrox card
I also tested on and old mac ibook with ATI card running 10.4.8 and on
that it works if i do
glOrtho(0, size[0], size[1]+1, -1, 1, 0)
Not very consistent. It seems to me that it might be more to do with the
OS rather than with the cards themselves. The XP versions I am running
are different but the Debian are pretty much the same.
I attach my example in case anyone wants to test it out his/her machine.
The glOrtho is on line 19 and i pasted different combinations of
setup the glOrtho
thanks!
enrike
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