import java.applet.Applet;
import java.awt.*;
import go.*;

class GoLightDemo extends GoInterface
{
    GoSphere  sphere;
    GoMatrix  currentLightPosition = new GoMatrix();
    GoMatrix  mouseDraggedLightPosition = new GoMatrix();
    int       xStart;
    int       yStart;

    GoLightDemo()
    {   
        //
        // Create a sphere to illustrate this demo.  A sphere
        // is a good shape for understanding how lighting works.
        //

        sphere = new GoSphere(1.0, 16, 16);

        //
        // Turn on LIGHT_0
        //

        go.light(Go.LIGHT_0, true);

        //
        // Set position of LIGHT_0 bases the current modelview matrix,
        // which is at the point the identity matrix.
        //

        setLightPosition();
    }

    //
    // Interface render method.
    //
    public void render()
    {
        //
        // Clear.
        //

        go.clear(Go.IMAGE);

        //
        // Draw.
        //
            
        go.color(0, 0, 1);       // blue
        sphere.renderSolid(go);
        go.color(1, 1, 0);       // yellow
        sphere.renderWire(go);
            
        //
        // Display.
        //

        swap();
    }

    //
    // Interface resized method.
    //
    public void resized(int width, int height)
    {
        //
        // Setup projection matrix.
        //

        go.push(Go.MATRIX_MODE);
        go.matrixMode(Go.PROJECTION);
        go.identity();
        if(width > height) {
            go.ortho(-1.0 * width / height, 1.0 * width / height,
                     -1.0, 1.0,
                     -1.0, 1.0);
        }
        else {
            go.ortho(-1.0, 1.0,
                     -1.0 * height / width, 1.0 * height / width,
                     -1.0, 1.0);
        }
        go.pop(Go.MATRIX_MODE);
    }

    //
    // Interface mousePressed method.
    //
    public void mousePressed(int x, int y)
    {
        //
        // Save values that will be used to track the
        // mouse in the mouseDragged() method.
        //
                        
        xStart = x;
        yStart = y;
    }

    //
    // Interface mouseReleased method.
    //
    public void mouseReleased(int x, int y)
    {
        //
        // Replace the currentLightPosition with the final result
        // of mouseDraggedLightPosition.
        //
                         
        for(int i = 0; i < 16; i++) {
            currentLightPosition.m[i] = mouseDraggedLightPosition.m[i];
        }
    }

    //
    // Interface mouseDragged method.
    //
    public void mouseDragged(int x, int y)
    {
        int xEnd = x;
        int yEnd = y;
                        
        //
        // Save the modelview matrix.
        //
                        
        go.push(Go.MODELVIEW);
                        
        //
        // Setup modelview matrix based on mouse position.
        //
                        
        go.identity();
        double xTheta = (yEnd - yStart) / 2;
        double yTheta = (xEnd - xStart) / 2;
        go.rotate(xTheta, 1, 0, 0);
        go.rotate(yTheta, 0, 1, 0);

        //
        // Post multiply current light position.
        //
                         
        go.multiply(currentLightPosition);
                         
        //
        // Setup the light position with the current modelview matrix.
        //
                        
        setLightPosition();
                        
        //
        // Save the "mouse dragged" light position so that 
        // currentLightPosition can be updated in mouseReleased().
        //
                         
        go.getModelview(mouseDraggedLightPosition);
                         
        //
        // Restore the modelview matrix.
        //
                        
        go.pop(Go.MODELVIEW);
                        
        //
        // Redisplay.
        //
                        
        rerender();
    }

    //
    // Light position.
    //
    void setLightPosition()
    {
        go.light(Go.LIGHT_0, Go.POSITIONAL, 0.0, 0.0, 1.75);
    }
}

public class light extends Applet
{
    public void init()
    {
        setLayout(new GridLayout(1, 1));
        add(new GoLightDemo());
    }
}