pyopengl-users

[PyOpenGL-Users] font rendering problem

[vwf <vw...@vu...>]

Hello PyOpenGL experts,


I have an ongoing saga of opengl problems. This time I try to tacle a
font rendering problem. It might be that there are new rendering
techniques available, but I still use a rather old technique.

The attached image shows the problem, the attached code produces it (on
my system, running Debian Linux, Lenny/stable). For it to run you need
Vera.ttf. The code is a small as I could get it without seriously
changing the functionality.

Does someone know how to fix it? If there is an entirely new approach, I
would like to know.

Thank you all,

Frits

Re: [PyOpenGL-Users] font rendering problem

[Dirk R. <dir...@gm...>]

	Hi Frits,

vwf wrote:
> Hello PyOpenGL experts,
> 
> 
> I have an ongoing saga of opengl problems. This time I try to tacle a
> font rendering problem. It might be that there are new rendering
> techniques available, but I still use a rather old technique.
> 
> The attached image shows the problem, the attached code produces it (on
> my system, running Debian Linux, Lenny/stable). For it to run you need
> Vera.ttf. The code is a small as I could get it without seriously
> changing the functionality.
> 
> Does someone know how to fix it? If there is an entirely new approach, I
> would like to know.

In 99% of the cases an image like that is caused by images that have odd width. 
By default OpenGL assumes image lines to start on a 4 byte boundary. if you have 
RGBA byte-sized pixels that's automatic, but for other sizes it may or may not 
work. You can try to add a glPixelStore(GL_UNPACK_ALIGNMENT, 1), that would 
avoid this problem.

Hope it helps

	Dirk

Re: [PyOpenGL-Users] font rendering problem

[Mike C. F. <mcf...@vr...>]

vwf wrote:
...
> Does someone know how to fix it? If there is an entirely new approach, I
> would like to know.
>   
Looks like a 90 degree rotation problem, that will cause the image to
get those diagonal lines (when width != height).  PyOpenGL automatically
sets tight packing (non-aligned) so the problem Dirk described shouldn't
happen.  Try doing a simple rotate on the image before you pass it to
PyOpenGL.

There are dozens of approaches to rendering text, you are using a
version ripped out of OpenGLContext by the look of it.  IIRC the
Pygame-generated font there needs to do a rotate in order to get to
OpenGL-compatible rendering format.

HTH,
Mike

-- 
________________________________________________
  Mike C. Fletcher
  Designer, VR Plumber, Coder
  http://www.vrplumber.com
  http://blog.vrplumber.com