Posted by Cyrille on Nov 19, 2010; 3:30pm
URL: https://forum.jogamp.org/Clear-status-about-GLCanvas-without-animator-tp1930475p1931149.html

I tried to call display() explicitly but it doesn't work.

In the sample application below, the canvas appears yellow at startup (its background color) while I expect it to be red (OpenGL clear color). If I call display() everytime the canvas is resized, the canvas flickers between yellow and red during the resize operation and randomly ends yellow or red.

package GLSLTest;

import java.awt.Color;
import java.awt.Component;
import java.awt.Frame;

import javax.media.opengl.GL;
import javax.media.opengl.GL2;
import javax.media.opengl.GLAutoDrawable;
import javax.media.opengl.GLCapabilities;
import javax.media.opengl.GLEventListener;
import javax.media.opengl.GLProfile;
import javax.media.opengl.awt.GLCanvas;
import javax.swing.BoxLayout;

public class Main
{
        static CanvasListener listener = new CanvasListener();

        public static void main(String[] args)
        {
                GLProfile.initSingleton();

                GLProfile profile = GLProfile.getMaxFixedFunc();
                GLCapabilities caps = new GLCapabilities(profile);
                GLCanvas canvas = new GLCanvas(caps);
                canvas.setBackground(Color.yellow);
                canvas.addGLEventListener(listener);

                Frame topLevelFrame = new Frame();
                topLevelFrame.setLayout(new BoxLayout(topLevelFrame, BoxLayout.Y_AXIS));
                topLevelFrame.add(canvas);
                topLevelFrame.setSize(400, 300);
                topLevelFrame.setVisible(true);

                // Animator animator = new Animator(canvas);
                // animator.start();

                canvas.display();
        }
}

class CanvasListener implements GLEventListener
{
        @Override
        public void display(GLAutoDrawable arg0)
        {
                GL2 gl = arg0.getGL().getGL2();
                gl.glClearColor(1.0f, 0.0f, 0.0f, 0.5f);
                gl.glClear(GL.GL_COLOR_BUFFER_BIT);

                System.out.println("display");
        }

        @Override
        public void dispose(GLAutoDrawable arg0)
        {
        }

        @Override
        public void init(GLAutoDrawable arg0)
        {
                Component canvas = (Component) arg0;
                System.out.println(canvas.getSize().toString());
        }

        @Override
        public void reshape(GLAutoDrawable arg0, int arg1, int arg2, int arg3, int arg4)
        {
        }
}