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transparent background rendering

Started by wlb2001 Apr 24, 2009 at 2:44 AM 1 replies 500+ views

Original Post

wlb2001

Apr 24, 2009 at 2:44 AM

Hi there! I am trying to implement a desktop 3d model viwer, which means I don't want to show the anything about window, just a 3d model itself.(windows plateform). I have tried SetLayeredWindowAttributes(), but that function not only make the window transparency but also make everyting draw in the framebuff transparency. And that method really decreases the FPS. By the way, there is anther problem confused me. glClearColor(0,0,0,0); unsigned char _Tbuf[40000]; unsigned char _Tbuf2[40000]; memset(_Tbuf2,0,40000*sizeof(unsigned char)); glDrawBuffer(GL_BACK); glDrawPixels(100,100,GL_RGBA,GL_UNSIGNED_BYTE,_Tbuf2); glReadBuffer(GL_BACK); glReadPixels(0,0,100,100,GL_RGBA,GL_UNSIGNED_BYTE,_Tbuf); the _Tbuf alpha channle always be 255, no matter what alpha value I set. Is that means the framebuff alpha channle is always 255? Thanks.

Brother Bob

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218

Brother Bob

Apr 24, 2009 at 3:45 AM

If you're not asking for an alpha channel for the frame buffer when defining the pixel format, you may not get one. If you don't have one, any read of the alpha channel will return 1.0 (or 255 for 8-bit integers). Check your alpha bits with glGetInteger and GL_ALPHA_BITS.

wlb2001

Author

wlb2001

Apr 24, 2009 at 4:37 AM

Really thanks for the help! I do forget to set the alpha bits when i set the pixelformat. Now I got the right result. But the problem is, I still didn't get an transparent background, even the alpha value in framebuffer is 0. So what can I do now?

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