import ij.IJ;
import ij.ImagePlus;
import ij.gui.ImageWindow;
import ij.plugin.PlugIn;
import ij.process.ColorProcessor;

import java.awt.Frame;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import java.nio.IntBuffer;
import javax.media.opengl.*;
import javax.media.opengl.glu.GLU;

// Note that a GLCanvas is not a window component Java knows about,
// and it will not appear in the ImageJ window menu.
// Also, even though it extends Canvas, its paint and update methods can't
// be used to draw on it, or the Graphics object be used to get at pixel values

public class OpenGLExample1_ implements PlugIn, GLEventListener {

	public OpenGLExample1_() { }

	public void run (String arg) {
		final Frame f = new Frame("OpenGL Canvas 1");
		f.addWindowListener(new WindowAdapter() {
			public void windowClosing (WindowEvent evt) {
				f.dispose();
			}
		});
		GLCanvas canvas1 =  new GLCanvas();
		canvas1.addGLEventListener(this);
		canvas1.setSize(300, 300);
		f.add(canvas1);
		f.pack();
		f.setVisible(true);
	}

// The following methods implement the GLEventListener interface

	public void init (GLAutoDrawable drawable) {
		GL gl = drawable.getGL();
		gl.glShadeModel(GL.GL_SMOOTH);            // Enables Smooth Shading
		gl.glClearColor(0.0f, 0.0f, 0.0f, 0.0f);  // Black Background
		gl.glClearDepth(1.0);                     // Depth Buffer Setup
		gl.glEnable(GL.GL_DEPTH_TEST);            // Enables Depth Testing
		gl.glDepthFunc(GL.GL_LEQUAL);             // The Type Of Depth Test To Do
		gl.glHint(GL.GL_PERSPECTIVE_CORRECTION_HINT, GL.GL_NICEST); // Really Nice Perspective Calculations
	}

	public void reshape (GLAutoDrawable drawable, int x, int y, int width, int height) {
		GL gl = drawable.getGL();
		if (height == 0) height = 1;
		float h = (float)width / (float)height;
		gl.glViewport(0, 0, width, height);
		gl.glMatrixMode(GL.GL_PROJECTION);
		gl.glLoadIdentity();
		GLU glu = new GLU();
		glu.gluPerspective(45.0, h, 1.0, 20.0);
		gl.glMatrixMode(GL.GL_MODELVIEW);
		gl.glLoadIdentity();
	}

	public void display (GLAutoDrawable drawable) {                       // Here's Where We Do All Drawing
		GL gl = drawable.getGL();
		gl.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT);  // Clear The Screen And The Depth Buffer
		gl.glLoadIdentity();                                          // Reset The View
		gl.glTranslatef(-1.5f, 0.0f, -6.0f);                          // Move Into The Screen And Left

		gl.glBegin(GL.GL_TRIANGLES);
		gl.glColor3f(1.0f, 0.0f, 0.0f);
		gl.glVertex3f(0.0f, 1.0f, 0.0f);
		gl.glColor3f(0.0f, 1.0f, 0.0f);
		gl.glVertex3f(1.0f, -1.0f, 0.0f);
		gl.glColor3f(0.0f, 0.0f, 1.0f);
		gl.glVertex3f(-1.0f, -1.0f, 0.0f);
		gl.glEnd();

		// transferPixels will be called every time the window is resized or moved
		transferPixels(drawable);
	}

	public void displayChanged (GLAutoDrawable drawable, boolean modeChanged, boolean deviceChanged) { }

	public void transferPixels (GLAutoDrawable drawable) {
		int width = drawable.getWidth();
		int height = drawable.getHeight();

		ColorProcessor proc = new ColorProcessor(width, height);
		ImagePlus implus = new ImagePlus("Lesson01 ImageJ", proc);
		if (!implus.lock()) {
			IJ.showMessage("Can't lock image");
			ImageWindow iw = implus.getWindow();
			if (iw != null)
				iw.close();
			return;
		}

		GL gl = drawable.getGL();
		//gl.glFlush();
		gl.glFinish();
		gl.glReadBuffer(GL.GL_FRONT);
		IntBuffer buffer = IntBuffer.allocate(3 * width * height);
			// pixels are returned separately by R, G and B components, hence the factor 3
		gl.glReadPixels(0, 0, width, height, GL.GL_RGB, GL.GL_INT, buffer);
		int[] pixels = buffer.array();

		int mask = 255 << 24;

		// Note that the OpenGL and ImageJ coordinate systems are inverse to each other along the y axis:
		// point (0,0) is at the lower left for OpenGL, and at the upper left for ImageJ
		for (int h=0; h<height; h++)
			for (int w=0; w<width; w++) {
				int r = pixels[3*(width*h+w)];
				int g = pixels[3*(width*h+w)+1];
				int b = pixels[3*(width*h+w)+2];
				proc.putPixel(w, height-h-1, (r&mask)>>7 | (g&mask)>>15 | b>>23);
					// if these bit operations look strange, it's because I don't fully
					// understand how OpenGL stores R, G and B values in integers
			}

		implus.show();
		implus.updateAndRepaintWindow();
		implus.unlock();
		IJ.showStatus("OpenGL image copied");
	}
}