BezierCurve

/*
appletviewer BezierCurve.java
<applet code="BezierCurve" width="500" height="300"></applet>
*/

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

public class BezierCurve extends Applet implements Runnable {
	Dimension	dim;
	Image		imgBack;
	Graphics	gBuf;
	int		iDiv = 20;	// 分割数
	int		iTime = 0;	// 時間
	int		iDiff = 1;	// 差分
	boolean		bUpdate = false;
	double[]	adX = new double[10];
	double[]	adY = new double[10];
	double[]	adX9 = new double[iDiv + 1];
	double[]	adY9 = new double[iDiv + 1];
	int[][]		aaiIndex = {{4,0},{5,1},{6,2},{7,4},{8,5},{9,7}};

public void init() {
		dim = getSize();
		imgBack = createImage(dim.width, dim.height);
		gBuf = imgBack.getGraphics();

adX[0] = -2.0;
		adY[0] = -1.0;
		adX[1] = -1.0;
		adY[1] =  1.0;
		adX[2] =  1.0;
		adY[2] =  1.0;
		adX[3] =  2.0;
		adY[3] = -1.0;

Thread t = new Thread(this);
		t.start();
	}

public void run() {
		while (true) {
			try {
				Thread.sleep(100);
			} catch (Exception e) {
			}
			bUpdate = true;
			repaint();
		}
	}

public void update(Graphics g) {
		paint(g);
	}

public void paint(Graphics g) {
		gBuf.clearRect(0, 0, dim.width, dim.height);

gBuf.setColor(Color.green);
		for (int i = -2; i <= 2; i++) {
			int iX = 250 + 100 * i;
			gBuf.drawLine(iX, 0, iX, dim.height);
		}
		for (int i = -1; i <= 1; i++) {
			int iY = 150 - 100 * i;
			gBuf.drawLine(0, iY, dim.width, iY);
		}

double	d1 = (double)iTime / (double)iDiv;
		double	d0 = 1.0 - d1;
		for (int i = 0; i < aaiIndex.length; i++) {
			int[] ai = aaiIndex[i];
			adX[ai[0]] = adX[ai[1]] * d0 + adX[ai[1] + 1] * d1;
			adY[ai[0]] = adY[ai[1]] * d0 + adY[ai[1] + 1] * d1;
		}
		adX9[iTime] = adX[9];
		adY9[iTime] = adY[9];

gBuf.setColor(Color.blue);
		drawPolyline(adX, adY, 4, 3);
		drawPolyline(adX, adY, 7, 2);

gBuf.setColor(Color.red);
		drawPolyline(adX9, adY9, 0, iTime + 1);

gBuf.setColor(Color.black);
		drawPolyline(adX, adY, 0, 4);

g.drawImage(imgBack, 0, 0, this);

if (bUpdate) {
			iTime += iDiff;
			if (iTime <= 0 || iDiv <= iTime) {
				iDiff = -iDiff;
			}
			bUpdate = false;
		}
	}

void drawPolyline(double[] adX, double[] adY, int iOffset, int iPoints) {
		int[]	aiX = new int[iPoints];
		int[]	aiY = new int[iPoints];

for (int i = 0; i < iPoints; i++) {
			aiX[i] = 250 + (int)(100 * adX[iOffset + i]);
			aiY[i] = 150 - (int)(100 * adY[iOffset + i]);
		}
		gBuf.drawPolyline(aiX, aiY, iPoints);
	}
}