// -*- compile-command: "javac -cp libs/lwjgl.jar Triangle.java" -*- */

import org.lwjgl.opengl.GL11;
import org.lwjgl.opengl.Display;
import org.lwjgl.opengl.DisplayMode;
import org.lwjgl.LWJGLException;

class Triangle {

    static float angle = 0.0f;
    final static float v1_x = (float)Math.cos(Math.PI * (1.0f / 6.0f));
    final static float v1_y = (float)Math.sin(Math.PI * (1.0f / 6.0f));
    final static float v2_x = (float)Math.cos(Math.PI * (5.0f / 6.0f));
    final static float v2_y = (float)Math.sin(Math.PI * (5.0f / 6.0f));
    final static float v3_x = (float)Math.cos(Math.PI * (9.0f / 6.0f));
    final static float v3_y = (float)Math.sin(Math.PI * (9.0f / 6.0f));

    private void init() {
        GL11.glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
        GL11.glShadeModel(GL11.GL_SMOOTH);

        GL11.glMatrixMode(GL11.GL_PROJECTION);
        GL11.glLoadIdentity();
        GL11.glOrtho(-1.2f, 1.2f, -1.2f, 1.2f, -1.0f, 1.0f);

        GL11.glMatrixMode(GL11.GL_MODELVIEW);
        GL11.glLoadIdentity();
    }

    private void display() {
        GL11.glClear(GL11.GL_COLOR_BUFFER_BIT);
        GL11.glPushMatrix();

        GL11.glRotatef(angle, 0.0f, 0.0f, 1.0f);
        GL11.glBegin(GL11.GL_TRIANGLES);
        GL11.glColor3f(1.0f, 0.0f, 0.0f);
        GL11.glVertex2f(v1_x, v1_y);
        GL11.glColor3f(0.0f, 1.0f, 0.0f);
        GL11.glVertex2f(v2_x, v2_y);
        GL11.glColor3f(0.0f, 0.0f, 1.0f);
        GL11.glVertex2f(v3_x, v3_y);
        GL11.glEnd();
        
        GL11.glPopMatrix();
    }

    private void start() {
        try {
            Display.setTitle("Triangle!");
            Display.setDisplayMode(new DisplayMode(512, 512));
            Display.create();
        } catch (LWJGLException e) {
            System.err.println("Could't create display. Exiting");
            System.exit(0);
        }

        init();

        while (!Display.isCloseRequested()) {
            angle += 0.02f;
            display();
            Display.update();
        }

        Display.destroy();
    }

    public static void main(String[] args) {
        new Triangle().start();
    }
}