Android 2D绘图(Canvas+paint)详解

目录：
1.重要类概述
2.重要类的常用方法
2.简单View绘制(圆、圆弧、矩形、弧形、圆角矩形、椭圆、文字等)
3.setXfermode(Xfermode xfermode)的运用

1.重要类概述
在2D绘制中我们常用的类，也是两个最重要的类就是Canvas(画布)和Paint(画笔)，通过Canvas我们可以设置
绘制的形状和路径，当然仅仅形状和路径是不行的，我们还需要颜色啊，阴影啊，透明度等等的设置，这时候就是Paint的
事情了，Paint的作用主要就是设置绘图的风格，下面我们就总结一下这两个类常用的方法。

2.重要类的常用方法
(1)Canvas：

构造类方法：

Canvas()        //构造方法
Canvas(Bitmap bitmap) //带参构造方法，创建一个以bitmap位图为背景的Canvas

裁切类方法：

		clipPath(Path path, Region.Op op) //根据特殊path组合裁切图像,Region.Op定义了Region支持的区域间运算种类。
		
		clipRect(Rect rect, Region.Op op) //根据矩形组合裁切图像
		
		clipRegion(Region region, Region.Op op)
		
		concat(Matrix matrix) //通过matrix的设置可以对绘制的图形进行绘制伸缩和位移

图形绘制类方法：

		drawArc(RectF oval, float startAngle, float sweepAngle, boolean useCenter, Paint paint) //绘制弧形
		
		drawBitmap(Bitmap bitmap, Rect src, RectF dst, Paint paint) //绘制bitmap位图
		
		drawPicture(Picture picture, RectF dst) //绘制图片
		
		drawCircle(float cx, float cy, float radius, Paint paint) //绘制圆
		
		drawLine(float startX, float startY, float stopX, float stopY, Paint paint) //绘制线
		
		drawLines(float[] pts, int offset, int count, Paint paint) //可以选择性的去掉一些数据绘制多条线
		
		drawOval(RectF oval, Paint paint) //绘制椭圆
		
		drawPath(Path path, Paint paint) //绘制路径
		
		drawPoint(float x, float y, Paint paint) //绘制点
		
		drawPoints(float[] pts, int offset, int count, Paint paint) //绘制多个点
		
		drawPosText(String text, float[] pos, Paint paint) //绘制文本，float[] pos指定每个文本位置
		
		drawRect(float left, float top, float right, float bottom, Paint paint) //绘制矩形
		
		drawRoundRect(RectF rect, float rx, float ry, Paint paint) //绘制圆角矩形
		
		drawText(String text, float x, float y, Paint paint) //绘制string文本
		
		drawTextOnPath(char[] text, int index, int count, Path path, float hOffset, float vOffset, Paint paint) //路径上绘制文本

填充类方法：

		drawRGB(int r, int g, int b) //使用RGB指定颜色填充canvas的bitmap画布
		
		drawARGB(int a, int r, int g, int b) //使用ARGB指定颜色填充canvas的bitmap画布

其他操作类方法：

		save() //保存Canvas状态，save之后，可以调用Canvas的平移、放缩、旋转、错切、裁剪等操作
		
		restore() //恢复Canvas之前保存的状态，防止save后对Canvas执行的操作对后续的绘制有影响
		
		rotate(float degrees, float px, float py) //旋转
		
		scale(float sx, float sy) //缩放
		
		skew(float sx, float sy) //扭曲
		
		translate(float dx, float dy) //平移

(2)Paint：
文本设置相关方法：

			isUnderlineText() //判断是否有下划线
			
			setUnderlineText(boolean underlineText) //设置下划线
			
			getLetterSpacing() //获取字符间的间距
			
			setLetterSpacing(float letterSpacing) //设置字符间距
			
			getFontSpacing() //获取行间距
			
			isStrikeThruText() //判断文本是否有删除线
			
			setStrikeThruText(boolean strikeThruText) //设置文本删除线
			
			getTextSize() //获取字体大小
			
			setTextSize(float textSize) //设置字体大小
			
			getTypeface() //获取文字字体类型
			
			setTypeface(Typeface typeface) //设置文字字体类型
			
			getTextSkewX() //获取斜体文字的值
			
			setTextSkewX(float skewX) //设置斜体文字的值，负数为右倾斜，正数为左倾斜 官方推荐-0.25
			
			getTextScaleX() //获取文字水平缩放值
			
			setTextScaleX(float scaleX) //设置文本水平缩放值
			
			getTextAlign() //获取文本对其方式
			
			setTextAlign(Paint.Align align) //设置文本对其方式
			
			ascent() //baseline之上至字符最高处的距离
			
			descent() //baseline下面到字符最低处的距离
			
			measureText(CharSequence text, int start, int end) //测绘文本的宽度
			
		        getTextBounds(char[] text, int index, int count, Rect bounds) //获取文本宽高


			getTextWidths(String text, int start, int end, float[] widths) //精确获取文本宽度
			
			getTextLocale() //获取文本语言地理位置
			
			setTextLocale(Locale locale) //设置文本地理位置，也就是设置对应的语言

绘图设置相关方法：

			//设置画笔颜色
			setARGB(int a, int r, int g, int b) 
			setAlpha(int a) 
			setColor(int color)
			
			//获取画笔颜色
			getAlpha() 
			getColor() 
			
			isAntiAlias() //判断是否抗锯齿
			
			setAntiAlias(boolean aa)  //设置抗锯齿，虽然耗资源耗时间，但是一般会开启
			
			getStyle() //获取画笔样式
			
			setStyle(Paint.Style style) //设置画笔样式,FILL：实心; FILL_OR_STROKE：同时实心和空心; STROKE：空心
			
			setStrokeCap(Cap cap) //设置画笔样式， 圆形(Cap.Round),方形(Cap.SQUARE)
			
			getStrokeWidth() //获取画笔的粗细大小
			
			setStrokeWidth(float width) //设置画笔的粗细大小
			
			clearShadowLayer() //清除阴影层
			
			setShadowLayer(float radius, float dx, float dy, int shadowColor) //设置阴影
			
			getXfermode() //获取图形绘制的像素融合模式
			
			setXfermode(Xfermode xfermode) //设置图形绘制的像素融合模式和叠加模式，就是新绘制的像素与Canvas上对应位置已有的像素按照混合规则进行颜色混合
			
			getShader() //获取图形的渲染方式
			
			setShader(Shader shader) //设置图形的渲染方式，分别有线性渲染(LinearGradient) 环形渲染(RadialGradient) 组合渲染(ComposeShader) 扫描渐变渲染/梯度渲染(SweepGradient)

其他方法：

			reset() //清除画笔复位

2.简单View绘制(圆、圆弧、矩形、弧形、圆角矩形、椭圆、文字等)
我们通过自定义View的形式来展示我们绘画的图形，所以在此之前我们需要搭建一个自定义View的模型
1.添加自定义类继承View类（待会我们将在onDraw()方法中绘制我们的图形）

package com.example.drawview;


import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;


/**
 * Created by elimy on 2016-10-11.
 */
public class DrawCircleView extends View {
    Paint paint;
    public DrawCircleView(Context context) {
        super(context);
    }


    public DrawCircleView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }


    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
    }
}

2.布局xml文件中应用(通过包名.类名的形式 (就像下面com.example.drawview.DrawTextView一样)指定我们定义的类)

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.drawview.MainActivity">


    <com.example.drawview.DrawTextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        />
</RelativeLayout>

接下来我们就可以在onDraw()方法中绘制我们的图形了

(1)圆的绘制
1.1 代码

package com.example.drawview;


import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;


/**
 * Created by elimy on 2016-10-11.
 */
public class DrawCircleView extends View {
    Paint paint;
    public DrawCircleView(Context context) {
        super(context);
    }


    public DrawCircleView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }


    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //初始化画笔
        paint = new Paint();
        //设置抗锯齿
        paint.setAntiAlias(true);
        //设置画笔颜色
        paint.setColor(getResources().getColor(R.color.colorAccent));
        //设置画笔要是，圆形/方形/其他
        paint.setStrokeCap(Paint.Cap.BUTT);
        //设置实心圆
        paint.setStyle(Paint.Style.FILL);
        //设置画笔大小
        paint.setStrokeWidth(2);
        //设置阴影
        paint.setShadowLayer(5,5,5, Color.BLUE);
        //绘制实心圆
        canvas.drawCircle(300,200,100,paint);
        //设置为空心
        paint.setStyle(Paint.Style.STROKE);
        //设置画笔大小
        paint.setStrokeWidth(3);
        //绘制
        canvas.drawCircle(500,200,100,paint);


    }


}

1.2 效果图

(2)矩形绘制
2.1 代码

package com.example.drawview;


import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.RectF;
import android.util.AttributeSet;
import android.view.View;


/**
 * Created by elimy on 2016-10-15.
 */
public class DrawRectView extends View {
    public DrawRectView(Context context) {
        super(context);
    }


    public DrawRectView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }


    @Override
    protected void onDraw(Canvas canvas){
        super.onDraw(canvas);
        Paint paint = new Paint();
        //设置抗锯齿
        paint.setAntiAlias(true);
        //设置画笔的样式
        paint.setStrokeCap(Paint.Cap.ROUND);
        //设置画笔粗细大小
        paint.setStrokeWidth(3);
        //设置画笔的所画图形的样式
        paint.setStyle(Paint.Style.FILL);
        //设置画笔的颜色
        paint.setColor(Color.GREEN);
        //绘制矩形 drawRect(left顶点X坐标, left顶点Y坐标, 右底部X坐标, 右底Y坐标, @NonNull Paint paint)
        canvas.drawRect(200,200,400,400,paint);
        //从新设置画笔所画图形样式
        paint.setStyle(Paint.Style.STROKE);
        //重新设置画笔大小
        paint.setStrokeWidth(5);
        //绘制
        RectF rect = new RectF(200,420,400,620);
        canvas.drawRect(rect,paint);




    }
}

2.2 效果图

(3)圆角矩形的绘制
3.1 代码

package com.example.drawview;


import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.RectF;
import android.util.AttributeSet;
import android.view.View;


/**
 * Created by elimy on 2016-10-14.
 */
public class DrawRoundRectView extends View {


    public DrawRoundRectView(Context context) {
        super(context);
    }


    public DrawRoundRectView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }


    @Override
    protected void onDraw(Canvas canvas){
      super.onDraw(canvas);
        //声明并初始化
        Paint paint = new Paint();
        //设置抗锯齿
        paint.setAntiAlias(true);
        //设置画出的图形是实心还是空心
        paint.setStyle(Paint.Style.FILL);
        //设置画笔粗细
        paint.setStrokeWidth(2);
        //设置画笔的样式
        paint.setStrokeCap(Paint.Cap.ROUND);
        //设置画笔颜色
        paint.setColor(getResources().getColor(R.color.colorPrimaryDark));
/*        if (Build.VERSION.SDK_INT>=21){
            //需要在API 21版本及其以后才能使用，和下面效果相同
            canvas.drawRoundRect(100,100,200,200,20,20,paint);
        }*/
        RectF rect = new RectF(200,200,400,400);
        canvas.drawRoundRect(rect,50,50,paint);
        //从新设置画笔大小
        paint.setStrokeWidth(5);
        //设置画笔画出的图形未空心
        paint.setStyle(Paint.Style.STROKE);
        //绘制矩形
        // RectF(left顶点x坐标, left顶点Y坐标, right边底部x坐标, right边底部Y坐标)
        RectF rect2 = new RectF(200,420,400,620);
        //绘制圆角矩形
        //drawRoundRect(@NonNull RectF rect, x方向上的圆角半径, Y方向上的圆角半径, @NonNull Paint paint)
        canvas.drawRoundRect(rect2,50,50,paint);


    }
}

3.2 效果图

(4)椭圆的绘制
4.1 代码

package com.example.drawview;


import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.RectF;
import android.os.Build;
import android.util.AttributeSet;
import android.view.View;


/**
 * Created by elimy on 2016-10-16.
 */
public class DrawOvalView extends View {
    public DrawOvalView(Context context) {
        super(context);
    }


    public DrawOvalView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    @Override
    protected void onDraw(Canvas canvas){
        super.onDraw(canvas);
        Paint paint = new Paint();
        //设置抗锯齿
        paint.setAntiAlias(true);
        //设置画笔笔尖样式
        paint.setStrokeCap(Paint.Cap.ROUND);
        //设置所画图形的填充样式
        paint.setStyle(Paint.Style.FILL);
        //设置画笔颜色
        paint.setColor(getResources().getColor(R.color.colorAccent));
        //实例化一个包裹椭圆的矩形，如果为正方形，则椭圆为圆
        RectF rectF = new RectF(200,200,500,400);
        //设置画布颜色,方便与paint.setColor()对比，看看他们的区别
        canvas.drawColor(Color.BLACK);
        //绘制椭圆
        canvas.drawOval(rectF,paint);
        //设置画笔的大小
        paint.setStrokeWidth(5);
        //设置绘画图形为空心
        paint.setStyle(Paint.Style.STROKE);
        //绘制
        if (Build.VERSION.SDK_INT>=21){
            //API 21以上才能用，与上面的绘画方式效果一致
            canvas.drawOval(200,450,500,650,paint);
        }
    }
}

4.2 效果图

(5)点的绘制
5.1 代码

package com.example.drawview;


import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;


/**
 * Created by elimy on 2016-10-16.
 */
public class DrawPointView extends View {
    public DrawPointView(Context context) {
        super(context);
    }


    public DrawPointView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    @Override
    protected void onDraw(Canvas canvas){
        super.onDraw(canvas);
        Paint paint = new Paint();
        paint.setAntiAlias(true);
        //设置画笔大小，我这边设置的大点，方便观察
        paint.setStrokeWidth(50);
        //设置画笔笔尖样式，默认为Paint.Cap.SQUARE，待会切换一下，你就会知道它的作用了
        // 网上有说在设置paint.setStrokeCap(Paint.Cap.ROUND|SQUARE);之前需要同时设置
        //paint.setStrokeJoin(Paint.Join.ROUND|MITER);我测试了好像不需要也能达到切换的目的
        paint.setStrokeCap(Paint.Cap.ROUND);
        paint.setColor(getResources().getColor(R.color.colorAccent));
        canvas.drawPoint(200,200,paint);


        paint.setStrokeCap(Paint.Cap.BUTT);
        paint.setColor(getResources().getColor(R.color.colorPrimary));
        canvas.drawPoint(300,200,paint);


        paint.setStrokeCap(Paint.Cap.SQUARE);
        paint.setColor(getResources().getColor(R.color.colorAccent));
        canvas.drawPoint(400,200,paint);


        paint.setStrokeCap(Paint.Cap.BUTT);
        paint.setColor(getResources().getColor(R.color.colorPrimary));
        canvas.drawPoint(500,200,paint);


        //设置画笔样式
        paint.setStrokeCap(Paint.Cap.ROUND);
        //设置画笔颜色
        paint.setColor(getResources().getColor(R.color.colorAccent));
        //绘制多个点
        canvas.drawPoints(new float[]{150,300,250,300,350,300,450,300,550,300},paint);


    }
}

5.2 效果图

(6)线段的绘制
6.1 代码

package com.example.drawview;


import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.LinearGradient;
import android.graphics.Paint;
import android.graphics.Shader;
import android.util.AttributeSet;
import android.view.View;


/**
 * Created by elimy on 2016-10-16.
 */
public class DrawLineView extends View {
    public DrawLineView(Context context) {
        super(context);
    }


    public DrawLineView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    @Override
    protected void onDraw(Canvas canvas){
        super.onDraw(canvas);
        Paint paint = new Paint();
        //设置抗锯齿
        paint.setAntiAlias(true);
        //设置画笔样式
        paint.setStrokeCap(Paint.Cap.ROUND);
        //设置画笔颜色
        paint.setColor(Color.RED);
        //设置画笔大小
        paint.setStrokeWidth(20);
        //画线段,参数分别是线段起始点的坐标和终点的坐标,和预设的画笔
        canvas.drawLine(100,200,600,200,paint);
        //LinearGradient(float x0, float y0, float x1, float y1, int colors[], float positions[],
        //TileMode tile)，（x0,y0) (x1,y1)源码上说是梯度的坐标，不是很懂，我个人理解为后面设置的每一种颜色渲染的长度，坐标间隔越小，渲染的颜色长度越短
        //int colors[]：指示需要渲染的颜色数组  float positions[]：可为null，为null时颜色均匀分布
        //TileMode tile：指示平铺模式，分别有REPEAT(重复) CLAMP(像素扩散) MIRROR(镜面投影)
        Shader mShader=new LinearGradient(0,0,100,100,
                new int[]{Color.RED,Color.GREEN,Color.BLUE,Color.YELLOW},
                null,Shader.TileMode.REPEAT);
        //设置画笔渲染渐变
        paint.setShader(mShader);
        //绘制渐变线段
        canvas.drawLine(100,300,600,300,paint);


    }
}

6.2 效果图

(7)路径的绘制
7.1 代码

package com.example.drawview;


import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.RectF;
import android.util.AttributeSet;
import android.view.View;


/**
 * Created by elimy on 2016-10-16.
 */
public class DrawPathView extends View {
    public DrawPathView(Context context) {
        super(context);
    }


    public DrawPathView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }


    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Paint paint = new Paint();
        //设置抗锯齿
        paint.setAntiAlias(true);
        //设置画笔笔尖样式
        paint.setStrokeCap(Paint.Cap.ROUND);
        //设置填充模式，默认为FILL
        paint.setStyle(Paint.Style.FILL);
        //设置画笔大小
        paint.setStrokeWidth(3);
        //设置颜色
        paint.setColor(getResources().getColor(R.color.colorPrimary));
        /*Path类的几个...To()方法：
        *   path.moveTo(x,y)移动到某个点
        *   path.lineTo(x,y)从起始点，默认(0,0)点绘制直线到(x,y)点
        *   path.arcTo()用来绘制弧形
        *   path.cubicTo()用来绘制贝塞尔曲线
        *   path.quadTo()也是绘制贝塞尔曲线的
        * */
        //实例化路径类
        Path path = new Path();
        //设置移动，不绘制
        path.moveTo(200, 200);
        //从(200，200)画到(200,400)
        path.lineTo(200, 400);
        //从(200,400)画到(400,400)
        path.lineTo(400, 400);
        //封闭曲线
        path.close();
        //绘制路径
        canvas.drawPath(path, paint);
        //设置颜色
        paint.setColor(getResources().getColor(R.color.colorAccent));
        //设置移动，不绘制
        Path path1 = new Path();
        path1.moveTo(200, 200);
        //从(200，200)画到(200,400)
        path1.lineTo(400, 200);
        //从(200,400)画到(400,400)
        path1.lineTo(400, 400);
        //封闭曲线
        path1.close();
        //绘制
        canvas.drawPath(path1, paint);
        //初始化路径
        Path path2 = new Path();
        //设置矩形
        RectF rectF = new RectF(420, 200, 620, 500);
        //取矩形包裹椭圆0°到270°的弧
        path2.arcTo(rectF, 0, 270);
        //封闭弧形
        path2.close();
        //设置填充实心
        paint.setStyle(Paint.Style.FILL);
        //设置画笔颜色
        paint.setColor(getResources().getColor(R.color.colorAccent));
        //绘制图形
        canvas.drawPath(path2, paint);
        /*
        *quadTo()绘制贝塞尔曲线
         */
        Path path3 = new Path();
        //移动到(200,620)点
        path3.moveTo(200, 620);
        //绘制贝塞尔曲线
        path3.quadTo(300, 420, 400, 620);
        //设置空心
        paint.setStyle(Paint.Style.STROKE);
        //绘制曲线
        canvas.drawPath(path3, paint);
        /*
        * cubicTo()绘制贝塞尔曲线
        * */
        Path path4 = new Path();
        //移动到(300,100)点
        path4.moveTo(300, 100);
        //绘制曲线
        path4.cubicTo(300, 100, 5, 300, 300, 500);
        //设置不填充
        paint.setStyle(Paint.Style.STROKE);
        //绘制
        canvas.drawPath(path4, paint);
    }
}

7.2 效果图

(8)路径文字+简单文字的绘制
8.1 代码

package com.example.drawview;


import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.Typeface;
import android.os.Build;
import android.util.AttributeSet;
import android.view.View;


/**
 * Created by elimy on 2016-10-16.
 */
public class DrawTextView extends View {
    public DrawTextView(Context context) {
        super(context);
    }


    public DrawTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    @Override
    protected void onDraw(Canvas canvas){
        super.onDraw(canvas);
        Paint paint = new Paint();
        //设置抗锯齿
        paint.setAntiAlias(true);
        //设置画笔颜色
        paint.setColor(getResources().getColor(R.color.colorPrimary));
        //设置画笔大小
        paint.setStrokeWidth(3);
        //设置字体大小
        paint.setTextSize(30);
        //设置文字样式
        paint.setTypeface(Typeface.DEFAULT_BOLD);
        String str = "我知道，你要说我很帅，哈啊哈哈哈哈,字不够长！";
        //全部显示，起点在(200,100)点
        canvas.drawText(str,50,100,paint);
        //截取4~9的字符串显示
        canvas.drawText(str,4,10,200,200,paint);
        //实例化路径
        Path path = new Path();
        //设置圆形状路径，Direction指示文字显示是逆时针向外还是顺时针向内 Path.Direction.CW|Path.Direction.CCW
        path.addCircle(400,400,110, Path.Direction.CW);
        //更具路径绘制文本
        canvas.drawTextOnPath(str,path,0,0,paint);


        Path path1 = new Path();
        if (Build.VERSION.SDK_INT>=21){
            //API 21以上
            path1.addOval(300,600,500,900, Path.Direction.CCW);
        }
        canvas.drawTextOnPath(str,path1,0,0,paint);
    }
}

8.2 效果图

(9)点文字的绘制
9.1 代码

package com.example.drawview;


import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;


/**
 * Created by elimy on 2016-10-16.
 */
public class DrawPosTextView extends View {
    public DrawPosTextView(Context context) {
        super(context);
    }


    public DrawPosTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    @Override
    protected void onDraw(Canvas canvas){
        super.onDraw(canvas);
        Paint paint = new Paint();
        //设置抗锯齿
        paint.setAntiAlias(true);
        //设置画笔颜色
        paint.setColor(getResources().getColor(R.color.colorAccent));
        //设置画笔到校
        paint.setStrokeWidth(5);
        //设置字体颜色
        paint.setTextSize(30);
        canvas.drawColor(Color.BLACK);
        canvas.drawPosText("你看我帅嘛？",new float[]{100,200,200,100,300,200,300,400,200,500,100,400},paint);
    }
}

9.2 效果图

3.setXfermode(Xfermode xfermode)的运用

setXfermode()方法主要是设置图形绘制的像素融合模式和叠加模式，就是新绘制的像素与Canvas上对应位置已有的像素按照混合规则进行颜色混合
以此实现多样的自定义View。

由于它的混合模式多达18种，下面我只是选取了其中几种，然后分别对不在Canvas上创建新Layer且不限制使用软件渲染与在Canvas上建立新
Layer并且个别模式采用软件渲染模式进行对比，看看他们的区别。如果又需要了解的原理的可以看看下面这篇博客：
http://blog.csdn.net/iispring/article/details/50472485

1)不在Canvas上创建新Layer且不限制使用软件渲染
(1)代码

package com.example.drawview;


import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.os.Build;
import android.util.AttributeSet;
import android.view.View;


/**
 * Created by elimy on 2016-10-17.
 */
public class XfermodeView extends View {
    public XfermodeView(Context context) {
        super(context);
    }


    public XfermodeView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }


    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);






        /*
        * 默认的Xfermode
        * */


        Paint paint = getPaint();
        //设置绘制圆的画笔颜色
        paint.setColor(getResources().getColor(R.color.colorPrimary));
        canvas.drawCircle(200, 200, 100, paint);
        //设置绘制圆角矩形的画笔颜色
        paint.setColor(getResources().getColor(R.color.colorAccent));
        if (Build.VERSION.SDK_INT >= 21)
            //API 21以上，当然最好是些兼容性好的，我这里只是为了方便
            canvas.drawRoundRect(200, 200, 300, 350, 10, 10, paint);


        /*
        * PorterDuff.Mode.ADD模式
        * */


        Paint paint1 = getPaint();
        paint1.setColor(getResources().getColor(R.color.colorPrimary));
        canvas.drawCircle(500, 200, 100, paint1);
        //设置像素融合模式
        paint1.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.ADD));
        paint1.setColor(getResources().getColor(R.color.colorAccent));
        if (Build.VERSION.SDK_INT >= 21)
            //API 21以上
            canvas.drawRoundRect(500, 200, 600, 350, 10, 10, paint1);
        //取消像素融合模式的设置
        paint1.setXfermode(null);




        /*
        * PorterDuff.Mode.CLEAR模式
        * */
        Paint paint2 = getPaint();
        paint2.setColor(getResources().getColor(R.color.colorPrimary));
        canvas.drawCircle(200, 500, 100, paint2);
        paint2.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
        paint2.setColor(getResources().getColor(R.color.colorAccent));
        if (Build.VERSION.SDK_INT >= 21)
            //API 21以上
            canvas.drawRoundRect(200, 500, 300, 650, 10, 10, paint2);
        paint2.setXfermode(null);


         /*
        * PorterDuff.Mode.DARKEN模式
        * */
        Paint paint3 = getPaint();
        paint3.setColor(getResources().getColor(R.color.colorPrimary));
        canvas.drawCircle(500, 500, 100, paint3);
        paint3.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DARKEN));
        paint3.setColor(getResources().getColor(R.color.colorAccent));
        if (Build.VERSION.SDK_INT >= 21)
            //API 21以上
            canvas.drawRoundRect(500, 500, 600, 650, 10, 10, paint3);
        paint3.setXfermode(null);
		
        /*
        * PorterDuff.Mode.LIGHTEN模式
        * */
        Paint paint4 = getPaint();
        paint4.setColor(getResources().getColor(R.color.colorPrimary));
        canvas.drawCircle(200, 800, 100, paint4);
        paint4.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.LIGHTEN));
        paint4.setColor(getResources().getColor(R.color.colorAccent));
        if (Build.VERSION.SDK_INT >= 21)
            //API 21以上
            canvas.drawRoundRect(200, 800, 300, 950, 10, 10, paint4);


         /*
        * PorterDuff.Mode.MULTIPLY模式
        * */
        Paint paint5 = getPaint();
        paint5.setColor(getResources().getColor(R.color.colorPrimary));
        canvas.drawCircle(500, 800, 100, paint5);
        paint5.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.MULTIPLY));
        paint5.setColor(getResources().getColor(R.color.colorAccent));
        if (Build.VERSION.SDK_INT >= 21)
            //API 21以上
            canvas.drawRoundRect(500, 800, 600, 950, 10, 10, paint5);
        paint5.setXfermode(null);


    }


    public Paint getPaint() {
        Paint paint = new Paint();
        paint.setAntiAlias(true);
        paint.setStyle(Paint.Style.FILL);
        paint.setStrokeWidth(5);
        return paint;
    }
}

(2)效果截图

2)在Canvas上建立新Layer并且个别模式采用软件渲染模式
(1)代码

package com.example.drawview;


import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.os.Build;
import android.util.AttributeSet;
import android.view.View;


/**
 * Created by elimy on 2016-10-17.
 */
public class XfermodeView extends View {
    public XfermodeView(Context context) {
        super(context);
    }


    public XfermodeView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }


    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);






        /*
        * 默认的Xfermode
        * */


        Paint paint = getPaint();
        //设置绘制圆的画笔颜色
        paint.setColor(getResources().getColor(R.color.colorPrimary));
        canvas.drawCircle(200, 200, 100, paint);
        //设置绘制圆角矩形的画笔颜色
        paint.setColor(getResources().getColor(R.color.colorAccent));
        if (Build.VERSION.SDK_INT >= 21)
            //API 21以上，当然最好是些兼容性好的，我这里只是为了方便
            canvas.drawRoundRect(200, 200, 300, 350, 10, 10, paint);


        /*
        * PorterDuff.Mode.ADD模式
        * */


        //canvas.saveLayer()在canvas原画布上见一个透明的layer
        int layerId = canvas.saveLayer(0, 0, canvas.getWidth(), canvas.getHeight(), null, Canvas.ALL_SAVE_FLAG);
        Paint paint1 = getPaint();
        paint1.setColor(getResources().getColor(R.color.colorPrimary));
        canvas.drawCircle(500, 200, 100, paint1);
        //设置像素融合模式
        paint1.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.ADD));
        paint1.setColor(getResources().getColor(R.color.colorAccent));
        if (Build.VERSION.SDK_INT >= 21)
            //API 21以上
            canvas.drawRoundRect(500, 200, 600, 350, 10, 10, paint1);
        //取消像素融合模式的设置
        paint1.setXfermode(null);
        //将新图层画到canvas上
        canvas.restoreToCount(layerId);




        /*
        * PorterDuff.Mode.CLEAR模式
        * */
        int layerId2 = canvas.saveLayer(0, 0, canvas.getWidth(), canvas.getHeight(), null, Canvas.ALL_SAVE_FLAG);
        Paint paint2 = getPaint();
        paint2.setColor(getResources().getColor(R.color.colorPrimary));
        canvas.drawCircle(200, 500, 100, paint2);
        paint2.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
        paint2.setColor(getResources().getColor(R.color.colorAccent));
        if (Build.VERSION.SDK_INT >= 21)
            //API 21以上
            canvas.drawRoundRect(200, 500, 300, 650, 10, 10, paint2);
        paint2.setXfermode(null);
        canvas.restoreToCount(layerId2);
         /*
        * PorterDuff.Mode.DARKEN模式
        * */
        int layerId3 = canvas.saveLayer(0, 0, canvas.getWidth(), canvas.getHeight(), null, Canvas.ALL_SAVE_FLAG);
        Paint paint3 = getPaint();
        paint3.setColor(getResources().getColor(R.color.colorPrimary));
        canvas.drawCircle(500, 500, 100, paint3);
        //禁用掉CPU硬件加速，采用软件渲染模式，因为DARKEN、LIGHTEN、OVERLAY等几种混合规则在GPU硬件加速效果展示不出来
        this.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
        paint3.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DARKEN));
        paint3.setColor(getResources().getColor(R.color.colorAccent));
        if (Build.VERSION.SDK_INT >= 21)
            //API 21以上
            canvas.drawRoundRect(500, 500, 600, 650, 10, 10, paint3);
        paint3.setXfermode(null);
        canvas.restoreToCount(layerId3);
        /*
        * PorterDuff.Mode.LIGHTEN模式
        * */
        int layerId4 = canvas.saveLayer(0, 0, canvas.getWidth(), canvas.getHeight(), null, Canvas.ALL_SAVE_FLAG);
        Paint paint4 = getPaint();
        paint4.setColor(getResources().getColor(R.color.colorPrimary));
        canvas.drawCircle(200, 800, 100, paint4);
        this.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
        paint4.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.LIGHTEN));
        paint4.setColor(getResources().getColor(R.color.colorAccent));
        if (Build.VERSION.SDK_INT >= 21)
            //API 21以上
            canvas.drawRoundRect(200, 800, 300, 950, 10, 10, paint4);
        paint4.setXfermode(null);
        canvas.restoreToCount(layerId4);
         /*
        * PorterDuff.Mode.MULTIPLY模式
        * */
        int layerId5 = canvas.saveLayer(0, 0, canvas.getWidth(), canvas.getHeight(), null, Canvas.ALL_SAVE_FLAG);
        Paint paint5 = getPaint();
        paint5.setColor(getResources().getColor(R.color.colorPrimary));
        canvas.drawCircle(500, 800, 100, paint5);
        paint5.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.MULTIPLY));
        paint5.setColor(getResources().getColor(R.color.colorAccent));
        if (Build.VERSION.SDK_INT >= 21)
            //API 21以上
            canvas.drawRoundRect(500, 800, 600, 950, 10, 10, paint5);
        paint5.setXfermode(null);
        canvas.restoreToCount(layerId5);
    }


    public Paint getPaint() {
        Paint paint = new Paint();
        paint.setAntiAlias(true);
        paint.setStyle(Paint.Style.FILL);
        paint.setStrokeWidth(5);
        return paint;
    }
}

(2)效果截图

3)PorterDuff.Mode的模式分类

		
        /** [0, 0] */
        CLEAR       (0),
        /** [Sa, Sc] */
        SRC         (1),
        /** [Da, Dc] */
        DST         (2),
        /** [Sa + (1 - Sa)*Da, Rc = Sc + (1 - Sa)*Dc] */
        SRC_OVER    (3),
        /** [Sa + (1 - Sa)*Da, Rc = Dc + (1 - Da)*Sc] */
        DST_OVER    (4),
        /** [Sa * Da, Sc * Da] */
        SRC_IN      (5),
        /** [Sa * Da, Sa * Dc] */
        DST_IN      (6),
        /** [Sa * (1 - Da), Sc * (1 - Da)] */
        SRC_OUT     (7),
        /** [Da * (1 - Sa), Dc * (1 - Sa)] */
        DST_OUT     (8),
        /** [Da, Sc * Da + (1 - Sa) * Dc] */
        SRC_ATOP    (9),
        /** [Sa, Sa * Dc + Sc * (1 - Da)] */
        DST_ATOP    (10),
        /** [Sa + Da - 2 * Sa * Da, Sc * (1 - Da) + (1 - Sa) * Dc] */
        XOR         (11),
        /** [Sa + Da - Sa*Da,
             Sc*(1 - Da) + Dc*(1 - Sa) + min(Sc, Dc)] */
        DARKEN      (12),
        /** [Sa + Da - Sa*Da,
             Sc*(1 - Da) + Dc*(1 - Sa) + max(Sc, Dc)] */
        LIGHTEN     (13),
        /** [Sa * Da, Sc * Dc] */
        MULTIPLY    (14),
        /** [Sa + Da - Sa * Da, Sc + Dc - Sc * Dc] */
        SCREEN      (15),
        /** Saturate(S + D) */
        ADD         (16),
        OVERLAY     (17);

上面这段代码来之源码，看了半天也没看出啥来，话说那些注释是啥意思呢，啥Sa又Da，宝宝头都大了？
网上看了一些文字解释，原来这样：
Sa->Source alpha->源图的Alpha通道
Da->Destination alpha->目标图的Alpha通道
Sc->Source color->源图的颜色
Dc->Destination color ->目标图的颜色
然后呢这样混合过后就组成了最后的ARGB值，形成最终的效果

作者：qq_28057577 发表于2016/10/18 11:50:01 原文链接

阅读：42 评论：0 查看评论

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