android 抛物线

package game.game; import org.loon.framework.android.game.core.graphics.LImage; import org.loon.framework.android.game.core.graphics.device.LGraphics; import org.loon.framework.android.game.utils.GraphicsUtils; import android.view.KeyEvent; public class Gamethis { //炮弹的发射点 int bulletX, bulletY; //炮弹的射程 int shotWidth = 50; //炮弹的射程高度 int shotHeight; //炮弹的速度 int shotSpeed = 3; //炮弹抛物线的系数 double a,b,c; int x1; int y1; int x2; int y2; int x3; int y3; int k; LImage xiaoqiu; boolean isrun; public Gamethis(int x,int y){ //初始化炮弹的发射点 this.bulletX = x; this.bulletY = y; //根据炮弹的发射点、高度、射程计算出炮弹抛物线的三点 x1 = bulletX; y1 = bulletY; x2 = bulletX+shotWidth/2; y2 = bulletY-shotHeight; x3 = bulletX+shotWidth; y3 = bulletY; xiaoqiu = GraphicsUtils.loadImage("res/paodan.png"); isrun = false; shotHeight = shotWidth/2-10; } public void move(){ //根据抛物线方程ax^2+bx+c=y，得方程组 //ax1^2+bx1+c=y1 //ax2^2+bx2+c=y2 //ax3^2+bx3+c=y3 //解方程组得抛物线的a,b,c b = ((y1-y3)*(x1*x1-x2*x2)-(y1-y2)*(x1*x1-x3*x3))/((x1-x3)*(x1*x1-x2*x2)-(x1-x2)*(x1*x1-x3*x3)); a = ((y1-y2)-b*(x1-x2))/(x1*x1-x2*x2); c = y1-a*x1*x1-b*x1; k = (int)(a*bulletX*bulletX+b*bulletX+c); //炮弹的速度 bulletX += shotSpeed; //炮弹将消失于小船的水平线 if(k > bulletY) { isrun = false; } } public void Paint(LGraphics g){ g.drawImage(xiaoqiu, bulletX, k); } public void keyPressed(int key) { // TODO Auto-generated method stub switch(key){ case KeyEvent.KEYCODE_DPAD_UP: shotWidth += 20; break; case KeyEvent.KEYCODE_DPAD_DOWN: shotWidth -= 20; break; case KeyEvent.KEYCODE_DPAD_CENTER: isrun = true; break; } } public void run() { // TODO Auto-generated method stub if(isrun){ move(); } } }