Pixel data from texture?

Graphics and GPU Programming Programming OpenGL

Started by MGB March 04, 2007 03:01 PM

7 comments, last by MGB 17 years, 1 month ago

288

Author

March 04, 2007 03:01 PM

Does anyone know how/if I can read the pixel data of a texture in OpenGL? I want to check my render-to-texture stuff is working, but all the commands I can see are for putting data *into* textures..?

Anonymous

March 04, 2007 03:28 PM

Attach the texture to FBO, make it current, and use glReadPixels.

dpadam450

2,403

March 04, 2007 03:34 PM

Well if its a texutre, just strap it to a quad and render that.

NBA2K, Madden, Maneater, Killing Floor, Sims http://www.pawlowskipinball.com/pinballeternal

daniel_i_l

295

March 04, 2007 03:41 PM

If you want the pixel data without passing the texture to the graphics card and wasting space you can take the data pointer (from whatever you use to load the texture) and then iterate through it and delete it before passing it on.

"We've all heard that a million monkeys banging on a million typewriters will eventually reproduce the entire works of Shakespeare. Now, thanks to the internet, we know this is not true." -- Professor Robert Silensky

MGB

288

Author

March 04, 2007 03:54 PM

Ah, the FBO stuff did it... ta!

glReadBuffer(GL_COLOR_ATTACHMENT0_EXT);char readBuff[texSize*texSize*3];glReadPixels(0,0,texSize,texSize,GL_RGB,GL_UNSIGNED_BYTE,readBuff);

umm not too sure what you meant there, daniel...

Nathan Baum

1,027

March 04, 2007 05:22 PM

You can also use glGetTexImage

MGB

288

Author

March 05, 2007 05:10 AM

Quote:Original post by Nathan Baum
You can also use glGetTexImage

Tsk - I actually looked through the Red Book for something like this and never saw it :o
Must prioritise sleep over gamedev some time :-/

[Edited by - Aph3x on March 5, 2007 5:10:56 AM]

daniel_i_l

295

March 05, 2007 05:58 AM

Quote:Original post by Aph3x
umm not too sure what you meant there, daniel...

When you load a texture you call the following commands:

GLuint texture;Texture = LoadPicture("pic.bmp"); //whatever you load the pic withglGenTextures(1, &texture);					glBindTexture(GL_TEXTURE_2D, texture);glTexImage2D(GL_TEXTURE_2D, 0, 3, Texture->sizeX, Texture->sizeY, 0, GL_RGB,GL_UNSIGNED_BYTE, Texture->data);free(Texture->data);

Now if you only want the data without actually generating a texture you can skip everything except the first line and use TextureData->data and the free it.