Double Buffer doubt

Is it possible to draw on the buffer that is being shown, or do I need always to swap the buffers to show the image?

I want to use it to make selection windows (using xor).

thanks and best regards,

Marcelo

No, I am quite sure there’s a GL call that is something like

glDrawBuffer(GL_FRONT);

If I am right this will make GL render to front buffer directly, giving you a thing like single-buffered windows.

I have not understood how do you plan to use it however, I guess it was just a curiosity.

EDIT: whoops, wrong enum.

[This message has been edited by Obli (edited 08-08-2003).]

It is posible, it would be treated like a bitmapped image.

The only problem is that the image must be static, you could not have any animation going on.

But if you want a 3D selection then you have to redraw the scene with the selected object
highlighted. So swap buffers is needed to make it look smooth.

I am think that you will need to keep swaping buffers and stuff.

Originally posted by marcelogsouza:
[b]Is it possible to draw on the buffer that is being shown, or do I need always to swap the buffers to show the image?

I want to use it to make selection windows (using xor).

thanks and best regards,

Marcelo[/b]

Recently I was also doing some kind of selection. Unfortunately I’ve encountered some problems. I am not sure but it also sounds like some double buffer thing. This is what I wanted to do :

  1. Draw “selection” scene. Each qube has its own color.
  2. Check which color is under mouse pointer (glReadPixels)
  3. Draw “real” scene
  4. SwapBuffers()
    I suppose that this method is incorrect since I get some crazy results! The whole scene is static but even in a point where a screen is black glReadPixels tells that there is some color and everything is wrong. Is it also something about buffers?

PS. Sorry for interrupting the post…

Nehe has a good tutor on picking(selecting) 3D objects, lesson 32 or 33 if I remember correctly.

Originally posted by Orzech:
[b]Recently I was also doing some kind of selection. Unfortunately I’ve encountered some problems. I am not sure but it also sounds like some double buffer thing. This is what I wanted to do :

  1. Draw “selection” scene. Each qube has its own color.
  2. Check which color is under mouse pointer (glReadPixels)
  3. Draw “real” scene
  4. SwapBuffers()
    I suppose that this method is incorrect since I get some crazy results! The whole scene is static but even in a point where a screen is black glReadPixels tells that there is some color and everything is wrong. Is it also something about buffers?

PS. Sorry for interrupting the post… [/b]

Originally posted by nexusone:
Nehe has a good tutor on picking(selecting) 3D objects, lesson 32 or 33 if I remember correctly.

Yeah I know. Thanks but I didn’t ask about it.