Jeannie Burleson (jeannie++at++cambertx.com)
Fri, 14 Jun 96 08:46:17 PDT
I am very new to OpenGL -- but I think that my question
is a pretty *basic* one. I am trying to do some pixel
manipulation (OpenGL) in my draw callback function (using
perfly).
Since, I've been having problems all I would like to
do is read in the frame buffer & write it back out again.
No changes, nothing. The code I've added in my callback
is:
...
PreDraw() ;
// my predraw stuff
glReadPixels ( 0, 0, x_window_size, y_window_size,
GL_RGBA, GL_BYTE, buffer ) ;
// this is where I'll add in my manipulation stuff
glRasterPos2i ( 0, 0 ) ;
glDrawPixels ( 0, 0, x_window_size, y_window_size,
GL_RGBA, GL_BYTE, buffer ) ;
pfDraw() ;
PostDraw() ;
Definitions:
struct PixelType
{
unsigned char r, g, b, a ;
} ;
int x_window_size = 1280 ;
int y_window_size = 1024 ;
PixelType *buffer = new PixelType [ x_window_size * y_window_size ] ;
I would have thought that these lines of code would do
essentially nothing. BUT, I end up with 2 images on the screen.
The first starts at the lower left hand corner, and the second
image starts to the right & above the middle point in the screen.
Most (3/4) of the second image isn't displayed since it falls
off the screen. I thought that the glRasterPos2i would force
the new image (glDrawPixels) to be drawn starting at the lower
left hand of the frame buffer.
I figure I must be using these routines incorrectly, but I
can't figure it out from the man pages. I would appreciate any
help!! Thanks in advance.
Jeannie
********************************************************
Jeannie M. Burleson email: jeannie++at++cambertx.com
Camber Corporation voice: (214) 991-5322 x160
4885 Alpha Rd. Suite 110 fax: (214) 991-5352
Dallas, TX 75244
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