package classwork;

import javax.media.opengl.*;
import jocode.*;
import jomodel.*;

/**
 * GLART_4_normal.java
 *
 * Very basic normal demo.  Just draws a triangle, calculates and
 * draws its normal.
 *
 * Uses the JOVector class to hold vertex positions and calculate normal.
 */
public class GLART_4_normal extends JOApp {
    float rotation = 0;

    /**
     * Main function just creates and runs the application.
     */
    public static void main(String args[]) {
    	GLART_4_normal app = new GLART_4_normal();
        app.run();
    }

    /**
     * Initialize OpenGL
     *
     */
    public void setup() {
        // Select the Projection Matrix (controls perspective)
        gl.glMatrixMode(GL.GL_PROJECTION);
        gl.glLoadIdentity();    // Reset The Projection Matrix

        // Define perspective
        glu.gluPerspective(
            45.0f,        // Field Of View
            (float)getWidth() / (float)getHeight(), // aspect ratio
            0.1f,         // near Z clipping plane
            100.0f);      // far Z clipping plane

        // Select The Modelview Matrix (controls model orientation)
        gl.glMatrixMode(GL.GL_MODELVIEW);

        // OpenGL won't draw backward facing triangles ("back faces")
        gl.glEnable(GL.GL_CULL_FACE);
    }

    /**
     * Render the scene.
     */
    public void draw() {
    	// hold triangle vertex positions in Vector objects
        JOVector v1 = new JOVector( 0.0f, 1.0f, 0.0f);
        JOVector v2 = new JOVector(-1.0f,-1.0f, 0.0f);
        JOVector v3 = new JOVector( 1.0f,-1.0f, 0.0f);

		// calculate normal of triangle
		JOVector normal = JOVector.getNormal(v1, v2, v3);

		// calculate center of triangle
		JOVector center = JOVector.avg(v1,v2,v3);

        // to turn the object
    	rotation += .5f;

        // lines will be 2 pixels wide
        gl.glLineWidth(2);

		// Clear screen and depth buffer
        gl.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT);

        // Select The Modelview Matrix (controls model orientation)
        // and reset the coordinate system to center of screen
        gl.glMatrixMode(GL.GL_MODELVIEW);
        gl.glLoadIdentity();

        // Where is the 'eye'
        glu.gluLookAt(
            0f, 0f, 4f,   // eye position
            0f, 0f, 0f,    // target to look at
            0f, 1f, 0f);   // which way is up

        // Draw the triangle and normal, rotating
        gl.glPushMatrix();
        {
        	// rotate on X Y and X axes
        	gl.glRotatef(rotation, .5f, 1, .3f);

            // draw a white triangle
            gl.glColor4f(1, 1, 1, 1);
			gl.glBegin(GL.GL_TRIANGLES);
			{
				gl.glVertex3f( 0.0f,  .75f, 0.0f); // Top
				gl.glVertex3f(-1.0f, -1.0f, 0.0f); // Bottom Left
				gl.glVertex3f( 1.0f, -1.0f, 0.0f); // Bottom Right
			}
			gl.glEnd();

			// draw the normal in red
			gl.glColor4f(1, 0, 0, 1);
			gl.glBegin(GL.GL_LINES);
			{
				gl.glVertex3f(center.x, center.y, center.z);
				gl.glVertex3f(center.x+normal.x, center.y+normal.y,	center.z+normal.z);
			}
			gl.glEnd();
		}
        gl.glPopMatrix();
    }
}