Re: [PyOpenGL-Users] glReadPixels

[Mike C. F. <mcf...@vr...>]

Ian Mallett wrote:
> Hello,
>
> So, I'm using glReadPixels(...) to get data for a screenshot.  I would
> really like to be able to get data from any framebuffer.  Currently,
> though, I can only get data from the screen framebuffer (or
> GL_COLOR_ATTACHMENT0_EXT).  I looked at glReadBuffer.  I'm using
> PyGame and PyOpenGL, and glGetString(GL_READ_BUFFER) returns None. 
> glReadBuffer(GL_BACK) crashes.
> What's going on?
Don't have your precise code.  Just added a glReadBuffer test to
PyOpenGL's tests modules, seems to work here, though my test code
doesn't do anything particularly interesting:

    def test_glDrawBuffers_list_valid( self ):
        """Test that glDrawBuffers with list argument where value is set"""
        previous = glGetIntegerv( GL_READ_BUFFER )
        fbo = glGenFramebuffersEXT(1)
        glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo)
        try:
            img1,img2 = glGenTextures(2)
            for img in img1,img2:
                glBindTexture( GL_TEXTURE_2D, img )
                glTexImage2D(
                    GL_TEXTURE_2D, 0, GL_RGB8, 
                    300, 300, 0, GL_RGB,
                    GL_INT,
                    None # no data transferred
                )
           

            glFramebufferTexture2DEXT(
                GL_FRAMEBUFFER_EXT,
                GL_COLOR_ATTACHMENT0_EXT,
                GL_TEXTURE_2D, img1, 0
            )
            glFramebufferTexture2DEXT(
                GL_FRAMEBUFFER_EXT,
                GL_COLOR_ATTACHMENT1_EXT,
                GL_TEXTURE_2D, img2, 0
            )
            a_type = constants.GLenum*2
            drawingBuffers = a_type(
                GL_COLOR_ATTACHMENT0_EXT,
                GL_COLOR_ATTACHMENT1_EXT,
            )
            glDrawBuffers(2, drawingBuffers )
            glReadBuffer( GL_COLOR_ATTACHMENT1_EXT )
            pixels = glReadPixels( 0,0, 10,10, GL_RGB, GL_UNSIGNED_BYTE )
            assert len(pixels) == 300, len(pixels)
        finally:
            glBindFramebufferEXT( GL_FRAMEBUFFER_EXT, 0 )
       
        glReadBuffer( previous )

Can you give me a script that shows the failure?

Good luck,
Mike

-- 
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  Mike C. Fletcher
  Designer, VR Plumber, Coder
  http://www.vrplumber.com
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