android canvas详解

代码说明：

Android中使用图形处理引擎，2D部分是android SDK内部自己提供，3D部分是用Open GL ES 1.0。今天我们主要要了解的是2D相关的，如果你想看3D的话那么可以跳过这篇文章。 大部分2D使用的api都在android.graphics和android.graphics.drawable包中。他们提供了图形处理相关的： Canvas、ColorFilter、Point(点)和RetcF(矩形)等，还有一些动画相关的：AnimationDrawable、 BitmapDrawable和TransitionDrawable等。以图形处理来说，我们最常用到的就是在一个View上画一些图片、形状或者自定义的文本内容，这里我们都是使用Canvas来实现的。你可以获取View中的Canvas对象，绘制一些自定义形状，然后调用View. invalidate方法让View重新刷新，然后绘制一个新的形状，这样达到2D动画效果。下面我们就主要来了解下Canvas的使用方法。 Canvas对象的获取方式有两种：一种我们通过重写View.onDraw方法，View中的Canvas对象会被当做参数传递过来，我们操作这个Canvas，效果会直接反应在View中。另一种就是当你想创建一个Canvas对象时使用的方法： 1 2 Bitmap b = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);   Canvas c =newCanvas(b); 上面代码创建了一个尺寸是100*100的Bitmap，使用它作为Canvas操作的对象，这时候的Canvas就是使用创建的方式。当你使用创建的Canvas在bitmap上执行绘制方法后，你还可以将绘制的结果提交给另外一个Canvas，这样就可以达到两个Canvas协作完成的效果，简化逻辑。但是android SDK建议使用View.onDraw参数里提供的Canvas就好，没必要自己创建一个新的Canvas对象。接下来我们看看Canvas提供我们哪些绘制图形的方法。我们创建一个自定义View对象，使用onDraw方法提供的Canvas进行绘制图形。 CanvasDemoActivity.java： 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 package com.android777.demo.uicontroller.graphics;                                                                                                                                      import android.app.Activity;   import android.content.Context;   import android.graphics.Canvas;   import android.graphics.Color;   import android.graphics.Paint;   import android.os.Bundle;   import android.view.View;                                                                                                                                      public class CanvasDemoActivity extends Activity {                                                                                                                                          @Override       protected void onCreate(Bundle savedInstanceState) {           super.onCreate(savedInstanceState);                                                                                                                                              setContentView(newCustomView1(this));                                                                                                                                          }                                                                                                                                          /**        * 使用内部类 自定义一个简单的View        * @author Administrator        *        */     class CustomView1 extends View{                                                                                                                                              Paint paint;                                                                                                                                              public CustomView1(Context context) {               super(context);               paint =newPaint();//设置一个笔刷大小是3的黄色的画笔               paint.setColor(Color.YELLOW);               paint.setStrokeJoin(Paint.Join.ROUND);               paint.setStrokeCap(Paint.Cap.ROUND);               paint.setStrokeWidth(3);           }                                                                                                                                              //在这里我们将测试canvas提供的绘制图形方法           @Override           protected void onDraw(Canvas canvas) {                                                                                                                                              }                                                                                                                                          }                                                                                                                                      } 执行结果是一片黑色的区域，因为在自定义的CustomView1中，我们没有做任何的绘制操作。canvas提供的绘制图形的方法都是以draw开头的，我们可以查看api： 从上面方法的名字看来我们可以知道Canvas可以绘制的对象有：弧线(arcs)、填充颜色(argb和color)、 Bitmap、圆(circle和oval)、点(point)、线(line)、矩形(Rect)、图片(Picture)、圆角矩形 (RoundRect)、文本(text)、顶点(Vertices)、路径(path)。通过组合这些对象我们可以画出一些简单有趣的界面出来，但是光有这些功能还是不够的，如果我要画一个仪表盘(数字围绕显示在一个圆圈中)呢？ 幸好Android还提供了一些对Canvas位置转换的方法：rorate、scale、translate、skew(扭曲)等，而且它允许你通过获得它的转换矩阵对象(getMatrix方法，不知道什么是转换矩阵？看这里) 直接操作它。这些操作就像是虽然你的笔还是原来的地方画，但是画纸旋转或者移动了，所以你画的东西的方位就产生变化。为了方便一些转换操作，Canvas 还提供了保存和回滚属性的方法(save和restore)，比如你可以先保存目前画纸的位置(save)，然后旋转90度，向下移动100像素后画一些图形，画完后调用restore方法返回到刚才保存的位置。下面我们就演示下canvas的一些简单用法： 1 2 3 4 protected void onDraw(Canvas canvas) {                                                                                                                                          canvas.drawCircle(100, 100, 90, paint);   } 效果是： 1 2 3 4 5 6 7 8 9 10 11 12 13 14 @Override   protected void onDraw(Canvas canvas) {                                                                                                                                          //绘制弧线区域                                                                                                                                          RectF rect =newRectF(0, 0, 100, 100);                                                                                                                                          canvas.drawArc(rect,//弧线所使用的矩形区域大小               0, //开始角度               90,//扫过的角度               false,//是否使用中心               paint);                                                                                                                                      } 使用下面的代码： 1 2 3 4 5 6 7 8 9 10 11 12 13 protected void onDraw(Canvas canvas) {                                                                                                                                          //绘制弧线区域                                                                                                                                          RectF rect =newRectF(0, 0, 100, 100);                                                                                                                                          canvas.drawArc(rect,//弧线所使用的矩形区域大小               0, //开始角度               90,//扫过的角度               true,//是否使用中心               paint);                                                                                                                                      } 两图对比我们可以发现，当 drawArcs(rect,startAngel,sweepAngel,useCenter,paint)中的useCenter为false时，弧线区域是用弧线开始角度和结束角度直接连接起来的，当useCenter为true时，是弧线开始角度和结束角度都与中心点连接，形成一个扇形。 1 2 3 4 5 protected void onDraw(Canvas canvas) {                                                                                                                                          canvas.drawColor(Color.BLUE);                                                                                                                                      } canvas.drawColor是直接将View显示区域用某个颜色填充满。 1 2 3 4 5 6 7 @Override   protected void onDraw(Canvas canvas) {                                                                                                                                          //画一条线       canvas.drawLine(10, 10, 100, 100, paint);                                                                                                                                      } Canvas.drawOval： 1 2 3 4 5 6 7 8 9 @Override   protected void onDraw(Canvas canvas) {                                                                                                                                          //定义一个矩形区域       RectF oval =newRectF(0,0,200,300);       //矩形区域内切椭圆       canvas.drawOval(oval, paint);                                                                                                                                      } canvas.drawPosText： 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 @Override   protected void onDraw(Canvas canvas) {                                                                                                                                          //按照既定点 绘制文本内容       canvas.drawPosText("Android777",newfloat[]{               10,10,//第一个字母在坐标10,10               20,20,//第二个字母在坐标20,20               30,30,//....               40,40,               50,50,               60,60,               70,70,               80,80,               90,90,               100,100       }, paint);                                                                                                                                      } canvas.drawRect： 1 2 3 4 5 6 7 8 9 10 @Override       protected void onDraw(Canvas canvas) {                                                                                                                                              RectF rect =newRectF(50, 50, 200, 200);                                                                                                                                              canvas.drawRect(rect, paint);                                                                                                                                          }                                                                                                                                      } canvas.drawRoundRect： 1 2 3 4 5 6 7 8 9 10 11 @Override   protected void onDraw(Canvas canvas) {                                                                                                                                          RectF rect =newRectF(50, 50, 200, 200);                                                                                                                                          canvas.drawRoundRect(rect,                           30,//x轴的半径                           30,//y轴的半径                           paint);                                                                                                                                      } canvas.drawPath： 1 2 3 4 5 6 7 8 9 10 11 12 @Override   protected void onDraw(Canvas canvas) {                                                                                                                                          Path path =newPath();//定义一条路径       path.moveTo(10, 10);//移动到 坐标10,10       path.lineTo(50, 60);       path.lineTo(200,80);       path.lineTo(10, 10);                                                                                                                                          canvas.drawPath(path, paint);                                                                                                                                      } canvas.drawTextOnPath： 1 2 3 4 5 6 7 8 9 10 11 12 13 @Override           protected void onDraw(Canvas canvas) {                                                                                                                                                  Path path =newPath();//定义一条路径               path.moveTo(10, 10);//移动到 坐标10,10               path.lineTo(50, 60);               path.lineTo(200,80);               path.lineTo(10, 10);                                                                                                                                      //          canvas.drawPath(path, paint);               canvas.drawTextOnPath("Android777开发者博客", path, 10, 10, paint);                                                                                                                                              } 位置转换方法，canvas.rorate和canvas.translate： 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 @Override   protected void onDraw(Canvas canvas) {                                                                                                                                          paint.setAntiAlias(true);       paint.setStyle(Style.STROKE);       canvas.translate(canvas.getWidth()/2, 200);//将位置移动画纸的坐标点:150,150       canvas.drawCircle(0, 0, 100, paint);//画圆圈                                                                                                                                          //使用path绘制路径文字       canvas.save();       canvas.translate(-75, -75);       Path path =newPath();       path.addArc(newRectF(0,0,150,150), -180, 180);       Paint citePaint =newPaint(paint);       citePaint.setTextSize(14);       citePaint.setStrokeWidth(1);       canvas.drawTextOnPath("http://www.android777.com", path, 28, 0, citePaint);       canvas.restore();                                                                                                                                          Paint tmpPaint =newPaint(paint);//小刻度画笔对象       tmpPaint.setStrokeWidth(1);                                                                                                                                          float  y=100;       int count = 60;//总刻度数                                                                                                                                          for(int i=0 ; i