Re: [uug] OpenGL help

[Lars Olson]

glReadPixels will do the trick, although it's also a little unwieldy, as it only returns one color component at a time.

e.g.:
float red;
glReadPixels(x, y, 1, 1, GL_RED, GL_FLOAT, &red);
// repeat for GL_GREEN and GL_BLUE

Lars

Michael Ryan Byrd wrote:

According to my 455 class you *can*, but it's difficult.

If I remember correctly, we used glutGetColor(int cell, int component)

http://www.opengl.org/developers/documentation/glut/spec3/node67.html#SECTIO
N00092000000000000000

in retrospect, it turned out to be unwieldy, so we made wrapper functions
anyway.

Cheers,

Ryan

----- Original Message -----
From: "David Smith" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Saturday, February 01, 2003 2:22 PM
Subject: Re: [uug] OpenGL help

Doesn anyone know of a way to have openGL return a
pixel color?

According to my 455 class, you can't. You must store the pixel colors
yourself. Put another way, you can't query the screen to see what color a
pixel is. This is most likely because OpenGL supports floats for pixel
coordintes. Ie, you can say glVertex2f(float x,float y) to turn on a
pixel. For it to store all the different colors for every possible float
value on your screen would be an enormous piece of memory.

It seems to be best to write a wrapper function to OpenGL's pixel
illuminating function and store the pixel's coordinates (use ints) and its
color (floats are okay).

--Dave



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