How do I Clear/Erase a rectangular area of a texture?

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Matt Rix
Member

Hey guys, this seems like it should be something pretty basic, but my OpenGL isn't that good yet.

I'm using a RenderTexture, and I want to be able to erase certain squares of it before I draw to them again. I don't want to clear the whole thing though, just parts of it. I need it to be fast too, if possible.

I was thinking I might be able to set the bytes of the texture to 0 within that area, but I think one of you might know a better way to do this using OpenGL(blendmodes or something?).

Thanks,

-Matt

Posted 2 years ago #
slipster216
Moderator

After you call begin, set it to only write into the alpha channel and draw something into the area you wish to erase:

glColorMask(TRUE, TRUE, TRUE, TRUE); // write to all channels of the render target

glColorMask(TRUE, TRUE, TRUE, FALSE); // write to just the color channels

glColorMask(FALSE, FALSE, FALSE, TRUE); // write just to the alpha channel

Posted 2 years ago #
Matt Rix
Member

Ahh, I think that's exactly what I was looking for, I'll let you know how it goes.

Posted 2 years ago #
Matt Rix
Member

Ah, just found this thread(I don't know how I missed it before), which is also really helpful on this topic: http://www.cocos2d-iphone.org/forum/topic/473

Posted 2 years ago #

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