java - glReadPixels() fails to fill ByteBuffer -

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well, i'm trying take screenshot window in opengl using lwjgl. here's code:

bytebuffer pixels = bytebuffer.allocatedirect(800*600*4); pixels.order(byteorder.nativeorder());  while(!display.iscloserequested()) {     glclear(gl_color_buffer_bit | gl_depth_buffer_bit);       render();     display.update();      // "screenshot" block     if(keyboard.iskeydown(keyboard.key_q)) {         pixels.clear();         glreadpixels(0, 0, 800, 600, gl_rgba, gl_unsigned_byte, pixels);         pixels.flip();          // pixels.position() , pixels.limit() tells there nothing in buffer         // ...     } }

and...

  • i've tried various versions of code, placing "screenshot" block before display.update(). , using combinations of glreadbuffer(gl_back/gl_front) , gldrawbuffer(gl_back/gl_front) no avail.

  • i've disabled opengl states , rendering, blank screen appears , tried using glreadpixels. blank screen supposes in buffer, nothing in buffer.

  • glgeterror() doesn't produce error.

  • i have similar c+ version works fine.

  • i'm running windows 7, opengl 4.10 , lwjgl version 2.7.1 on nvidia corporation geforce gts 450/pci/sse2.

so, what's problem? ideas? in advance.

pixels.position() , pixels.limit() tells there nothing in buffer

do they? think more foolproof method @ contents of buffer.

also, display.update swaps buffers. contents of buffer undefined after swap. should either read front buffer (not idea) or read buffer before swapping.


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