color_chooser_canvas.java

本光盘是《J2ME无线移动游戏开发》一书的配套光盘

package ch06;

import javax.microedition.lcdui.*;

//该类实现一个简单的颜色选择器
public class Color_Chooser_Canvas
    extends Canvas {
  //声明一个代表当前合成颜色的int型属性变量
  int rgbColor;

  //声明一个代表当前操作三原色彩条的索引int型属性变量
  int ndx = 0;

  //声明一个代表边框线条宽度的int型属性变量
  static final int BORDER = 2;

  //声明一个代表RGB三原色彩条高度的int型属性变量
  static final int BAR_H = 14;

  //初始化绘制上下文使用的颜色
  public Color_Chooser_Canvas() {
    setColor(0xffff00);
  }

  //用指定RGB设置当前颜色
  public void setColor(int RGB) {
    rgbColor = RGB;
  }

  //获取当前绘制上下文使用的颜色
  public int getColor() {
    return rgbColor;
  }

  //绘制画板
  protected void paint(Graphics g) {
    //获取屏幕宽度和高度
    int w = getWidth();
    int h = getHeight();

    //设置合成颜色面板矩形框的宽度、高度和y坐标
    int sample_w = w - 1;
    int sample_h = h - (BAR_H + BORDER) * 3;
    int sample_y = BORDER;

    //设置RGB三原色彩条的y坐标
    int b_y = sample_y + sample_h + BORDER * 2;
    int g_y = b_y + BAR_H;
    int r_y = g_y + BAR_H;

    //填充整个屏幕的背景色为黑色
    g.setColor(0x000000);
    g.fillRect(0, 0, w, h);

    //使用合成颜色填充颜色面板矩形
    g.setColor(rgbColor);
    g.fillRect(BORDER, sample_y, sample_w, sample_h);

    /*
     3.绘制RGB三原色彩条
     */
    int blue = (rgbColor >> 0) & 0xff;
    g.setColor(0, 0, 255);
    g.fillRect(20, b_y, blue / 4, 10);

    int green = (rgbColor >> 8) & 0xff;
    g.setColor(0, 255, 0);
    g.fillRect(20, g_y, green / 4, 10);

    int red = (rgbColor >> 16) & 0xff;
    g.setColor(255, 0, 0);
    g.fillRect(20, r_y, red / 4, 10);

    /*
     4.绘制RGB三原色的当前取值
     */
    g.setColor(255, 255, 255);
    g.drawString(Integer.toString(blue),
                 18, b_y - 3, Graphics.RIGHT | Graphics.TOP);
    g.drawString(Integer.toString(green),
                 18, g_y - 3, Graphics.RIGHT | Graphics.TOP);
    g.drawString(Integer.toString(red),
                 18, r_y - 3, Graphics.RIGHT | Graphics.TOP);

    /*
     5.绘制白色边框
     */
    if (ndx >= 0) {
      int y = b_y + ndx * BAR_H;
      g.drawRect(20, y, 63, 10);
    }

  }

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

  /*
   6.响应按键事件
   */
  protected void keyPressed(int key) {
    int action = getGameAction(key);
    int dir = 0;
    switch (action) {
      case RIGHT:
        dir += 1;
        break;
      case LEFT:
        dir -= 1;
        break;
      case UP:
        ndx -= 1;
        break;
      case DOWN:
        ndx += 1;
        break;
      default:
        return;
    }

    if (ndx < 0) {
      ndx = 0;
    }
    if (ndx > 2) {
      ndx = 2;
    }
    if (ndx >= 0) {
      int v = (rgbColor >> (ndx * 8)) & 0xff;
      v += dir * 0x20;
      if (v < 0) {
        v = 0;
      }
      if (v > 255) {
        v = 255;
      }
      int mask = 0xff << (ndx * 8);
      rgbColor = (rgbColor & ~mask) | v << (ndx * 8);
    }
    repaint();
  }
}