line_stroke_canvas.java

本光盘是《J2ME无线移动游戏开发》一书的配套光盘

package ch05;

import java.io.*;
import javax.microedition.lcdui.*;
import javax.microedition.lcdui.game.*;

public class Line_Stroke_Canvas
    extends GameCanvas {

  //获取绘制上下文
  Graphics g = getGraphics();

  //声明一个代表线宽的int型属性变量
  int lineWidth = 1;

  //变量w和h为模拟器的当前屏幕宽度和高度
  int w = getWidth();
  int h = getHeight();

  //构造器
  public Line_Stroke_Canvas() throws IOException {
    //支持按键事件
    super(false);
    setTitle("改变直线宽度实例");
  }

  //启动绘制
  public void start() {
    render(g, 1);
  }

  /*
   3.绘制方法
   */
  void render(Graphics g, int width) {
    //刷新屏幕为白色
    g.setColor(255, 255, 255);
    g.fillRect(0, 0, w, h);

    //设置线体颜色为红色
    g.setColor(0xff0000);

    for (int i = 0; i < width; i = i + 1) {
      g.drawLine(w / 3 - i, h / 3 - i, w - w / 3 + i, h / 3 - i);
      g.drawLine(w - w / 3 + i, h / 3 - i, w - w / 3 + i, h - h / 3 + i);
      g.drawLine(w - w / 3 + i, h - h / 3 + i, w / 3 - i, h - h / 3 + i);
      g.drawLine(w / 3 - i, h - h / 3 + i, w / 3 - i, h / 3 - i);
    }
    flushGraphics();
  }

  //响应连续按键事件
  public void keyRepeated(int key) {
    keyPressed(key);
  }

  /*
   4.响应按键事件
   */
  public void keyPressed(int key) {

    int action = getGameAction(key);

    switch (action) {
      case RIGHT:
        if (lineWidth > 19) {
          lineWidth = 20;
        }
        else {
          lineWidth += 1;
        }
        break;
      case LEFT:
        if (lineWidth < 2) {
          lineWidth = 1;
        }
        else {
          lineWidth -= 1;
        }
        break;
      case UP:
        if (lineWidth > 19) {
          lineWidth = 20;
        }
        else {
          lineWidth += 1;
        }
        break;
      case DOWN:
        if (lineWidth < 2) {
          lineWidth = 1;
        }
        else {
          lineWidth -= 1;
        }
        break;
      default:
        return;
    }
    render(g, lineWidth);
  }
}