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2D clipping problem - Printable Version

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2D clipping problem - McSebi - Feb 22, 2005 01:55 PM

Hi, this is my code for creating a context for a 2D view:

glViewport(0, 0, window_width, window_height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, window_width, window_height, 0, -1.0, 1.0);
glDisable(GL_DEPTH_TEST);

Everything looks ok, but every quad with negative coordinates will now be clipped away, which make objects disappear too soon when moving out of the window left or up.

I do it like this:

glBegin(GL_QUADS);
glVertex2s(rect.GetLeft(), rect.GetTop());
glVertex2s(rect.GetRight(), rect.GetTop());
glVertex2s(rect.GetRight(), rect.GetBottom());
glVertex2s(rect.GetLeft(), rect.GetBottom());
glEnd();

if rect.GetLeft() or rect.GetTop() is lower than 0 the whole rect won't be drawn even if parts of it should be visible!?! Why that?

-Sebastian


2D clipping problem - arekkusu - Feb 22, 2005 03:04 PM

What hardware/OS is this happening on?


2D clipping problem - McSebi - Feb 22, 2005 07:28 PM

OS 10.3.8 G5 tower with ATI 9600 card


2D clipping problem - arekkusu - Feb 22, 2005 10:28 PM

That definitely should not be happening. Are you sure your coordinates are valid all the time? (i.e. GetRight() returns a short, not an unsigned short?)

If the project is small, and doesn't depend on any weird 3rd party libraries, post a link to an archive and we'll take a look.


2D clipping problem - McSebi - Feb 22, 2005 11:37 PM

Thanks for this offer. I've figured it out... It was not in my drawing code. I've found out my draw function was not called at all when coordinates were negative...