OpenGL - Image == null when tryint to convert byte array to BufferedImage

Question

I am trying to get the screen using glReadPixels() then converting that into an image. I get an error saying image == null.

ByteBuffer _frame = ByteBuffer.allocate( 4 * Main.gui.glCanvas.getWidth() * Main.gui.glCanvas.getHeight() );
    System.out.println( "Num Pixels " + Main.width * Main.height );
    gl.glReadPixels(
            0,
            0,
            Main.gui.glCanvas.getWidth(),
            Main.gui.glCanvas.getHeight(),
            GL3.GL_RGBA,
            GL3.GL_UNSIGNED_BYTE,
            _frame
            );

    try {
        BufferedImage bi = ImageIO.read( new ByteArrayInputStream( _frame.array() ) );
        ImageIO.write( bi, "png", new File( "Slices/slicu.png" ) );
    } catch ( Exception e ) {
        System.out.println( e.getMessage() + " @ Filler.draw()" );
        e.printStackTrace();
    }

gouessej · Accepted Answer · 2014-03-31 07:57:54Z

2

Rather use com.jogamp.common.nio.Buffers.newDirectByteBuffer() instead of ByteBuffer.allocate(). If you use an undirect NIO buffer here, JOGL will have to make a direct NIO buffer under the hood and you can't be sure that a NIO buffer is backed by an array anyway, it can be null. Then, create an array and copy the content of your buffer into it.

You could use com.jogamp.opengl.util.awt.Screenshot, com.jogamp.opengl.util.GLReadBufferUtil or com.jogamp.opengl.util.awt.AWTGLReadBufferUtil instead, there are some examples on Github in jogl-demos.

I advise you to ask your questions about JOGL rather on our official forum.

answered Mar 31, 2014 at 7:57

gouessej

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