OpenGL "1 to 1" Pixel Setup?

SDL Development
1

Okay, I’m new so forgive if this is a stupid question.

I’ve been playing around with OpenGL trying to use it for some really basic
2D stuff for now (until I get better) but I can’t seem to find a way to set
up OGL so that when I draw a GL_QUADS using points (-1, 1), (1, 1), (1, -1),
and (-1, -1), it fills up ONLY a 2x2 pixel square… This code:

glBegin(GL_QUADS);
glVertex2f(-1, 1);
glVertex2f(1, 1);
glVertex2f(1, -1);
glVertex2f(-1, -1);
glEnd();

Fills the entire space with the polygon. I don’t want to have to say
something like "glVertex3f((spriteX/screenW), (spriteY/screenH),
(spriteLayer/maxDepth)); in order to get my exact positioning.

Anyhow, help would be appreciated.

–Scott

2

You should check the glOrtho function to setup an orthogonal view in
your projection matrix.

HTH

Marc

Scott Harper wrote:> Okay, I’m new so forgive if this is a stupid question.

I’ve been playing around with OpenGL trying to use it for some really basic
2D stuff for now (until I get better) but I can’t seem to find a way to set
up OGL so that when I draw a GL_QUADS using points (-1, 1), (1, 1), (1, -1),
and (-1, -1), it fills up ONLY a 2x2 pixel square… This code:

glBegin(GL_QUADS);
glVertex2f(-1, 1);
glVertex2f(1, 1);
glVertex2f(1, -1);
glVertex2f(-1, -1);
glEnd();

Fills the entire space with the polygon. I don’t want to have to say
something like "glVertex3f((spriteX/screenW), (spriteY/screenH),
(spriteLayer/maxDepth)); in order to get my exact positioning.

Anyhow, help would be appreciated.

–Scott

SDL mailing list
SDL at libsdl.org
http://www.libsdl.org/mailman/listinfo/sdl

3

look into “glViewport” and “glOrtho”…> ----- Original Message -----

From: lareon@comcast.net (Scott Harper)
To:
Sent: Monday, May 10, 2004 6:39 PM
Subject: [SDL] OpenGL “1 to 1” Pixel Setup?

Okay, I’m new so forgive if this is a stupid question.

I’ve been playing around with OpenGL trying to use it for some really
basic
2D stuff for now (until I get better) but I can’t seem to find a way to
set
up OGL so that when I draw a GL_QUADS using points (-1, 1), (1, 1),
(1, -1),
and (-1, -1), it fills up ONLY a 2x2 pixel square… This code:

glBegin(GL_QUADS);
glVertex2f(-1, 1);
glVertex2f(1, 1);
glVertex2f(1, -1);
glVertex2f(-1, -1);
glEnd();

Fills the entire space with the polygon. I don’t want to have to say
something like "glVertex3f((spriteX/screenW), (spriteY/screenH),
(spriteLayer/maxDepth)); in order to get my exact positioning.

Anyhow, help would be appreciated.

–Scott

SDL mailing list
SDL at libsdl.org
http://www.libsdl.org/mailman/listinfo/sdl