Hi John,
I cannot say, what the problem is,
but the possible solution is to use pbo with glReadPixels so that you read
previous frame - and all reading is async - not slowing app at all
here is a code for you
//somewhere after rendering
glReadBuffer(GL_FRONT);
// get next buffer's index
unsigned int iNextBuffer = (_iCurrentBuffer + 1) % N_MAX_BUFFERS;
// kick of readback of current front-buffer
// into the next buffer
glBindBuffer(GL_PIXEL_PACK_BUFFER, _aPixelBuffer[iNextBuffer]);//bind
pbo1
glReadPixels(0, 0, m_width, m_height, GL_BGRA,
GL_UNSIGNED_BYTE, BUFFER_OFFSET(0));//readback
// map the current buffer containing the
// image read back the previous time around
glBindBuffer(GL_PIXEL_PACK_BUFFER_EXT,
_aPixelBuffer[_iCurrentBuffer]);//bind pbo2
_pPixels = static_cast<unsigned char *>(glMapBuffer(GL_PIXEL_PACK_BUFFER,
GL_READ_ONLY));
if(_pPixels)
{
//something like:
memcpy(image,_pPixels,m_width*m_height*4);
// unmap the buffer
if (!glUnmapBuffer(GL_PIXEL_PACK_BUFFER))
{
std::cerr << "Couldn't unmap pixel buffer. Exiting\n";
assert(false);
}
}
// unbind readback buffer to not interfere with
// any other (traditional) readbacks.
glBindBuffer(GL_PIXEL_PACK_BUFFER, 0);
// make next-buffer the current buffer
_iCurrentBuffer = iNextBuffer;
glReadBuffer(GL_BACK);
make sure you have inited buffers
glGenBuffers(N_MAX_BUFFERS, _aPixelBuffer);
for (unsigned int iBuffer = 0; iBuffer < N_MAX_BUFFERS; ++iBuffer)
{
glBindBuffer(GL_PIXEL_PACK_BUFFER, _aPixelBuffer[iBuffer]);
glBufferData(GL_PIXEL_PACK_BUFFER, m_width*m_height*4, NULL,
GL_STATIC_READ);
errorcode = glGetError();
}
glBindBuffer(GL_PIXEL_PACK_BUFFER, 0);
and that you delete them after use
glBindBufferARB(GL_PIXEL_PACK_BUFFER_EXT, 0);
glDeleteBuffersARB(N_MAX_BUFFERS, _aPixelBuffer);
Regards
Sergey
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