Reflections & off screen rendering

[jwrennie]

Hi all,

I hope this is suitable for the advacned area.

I need to figure out how to create a refelctive ball in the middle of a room for an assignment at university.

The only problem i have come across is dynamically creating the textures for the ball.

Is it possible in opengl to render an image to an off screen buffer instead of onto the screen ?

If so how ? I've had a look around and cant find anything on it.

A simple link will suffice if i have missed it in my searches.

Thanks in advance

Jason

[Olive]

If you're hardware supports it, you can use pbuffers and guess what, if you go take a look at opengl.org there's a helper class in C++ and Delphi for creating those !! PBuffers are just offscreen rendering buffers.

[Nutty]

Reflective as in cube mapping?

Maybe take a look at my real time cube mapping demo. A big ball in a big room, with objects moving around it. Dynamically creates the cube map each frame too.

Should be similar to what you need, perhaps?

Nutty www.nutty.org (http://www.nutty.org)

[Bob]

Instead of using pbuffers, which I believe is "trur" offscreen buffers, you can use the back buffer. It won't show up on screen unless you swap the buffers.

[jwrennie]

thanks everybody.

With the back buffering option, is there a way to access the pixel information in the buffer, so i can build a texture to map onto the reflecting object.

Jason

[jwatte]

glCopyTexSubImage()

[cass]

Also, if you're doing this with GeForce hardware and Release 10 drivers, I would strongly encourage using automatic mipmap generation. It's really simple:

glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP_SGIS, GL_TRUE);

Then updates to level 0 automatically update the mipmaps, and mipmapping relection maps is pretty important.

Thanks -
Cass

[jwrennie]

It has to run under mesa, software rendering on, remotely from a sparc on an Xterminal.

Speed isn't important , as where just rendering a static image.

It just needs to look good, and not use any hardware specific stuff.

Jason

[DaViper]

Originally posted by cass:

Also, if you're doing this with GeForce hardware and Release 10 drivers, I would strongly encourage using automatic mipmap generation. It's really simple:

glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP_SGIS, GL_TRUE);


I would love to use that, but I am still missing Release 10 drivers for Linux... http://www.opengl.org/discussion_boards/ubb/frown.gif

Chris