Android中的自绘View的那些事儿（八）之 Paint的高级用法

我们在《Android中的自绘View的那些事儿（一）》中简单介绍过Paint和Canvas的一些常用方法和实例使用。其中，一句话提到Paint中有方法：setStrokeCap、setStrokeJoin 和 setPathEffect。今天我们就来针对这三个方法来进一步讲解其使用效果。

setStrokeCap

setStrokeCap(Paint.Cap cap);当Paint的setStyle为STROKE或FILL_OR_STROKE时，设置画笔的线冒样式，值有：Cap.BUTT、Cap.ROUND（圆形样式）和Cap.SQUARE（方形样式）。
示例：public class MyView extends View {

private Paint mPaint;

public MyView(Context context) {
this(context, null, 0);
}
public MyView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public MyView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);

mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setColor(0xffff0000);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeWidth(20);
}

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

mPaint.setStrokeCap(Paint.Cap.BUTT);
canvas.drawLine(100, 100, 500, 100, mPaint);

mPaint.setStrokeCap(Paint.Cap.ROUND);
canvas.drawLine(100, 200, 500, 200, mPaint);

mPaint.setStrokeCap(Paint.Cap.SQUARE);
canvas.drawLine(100, 300, 500, 300, mPaint);
}
}效果：

setStrokeJoin

setStrokeJoin(Paint.Join join);当setStyle为STROKE或FILL_OR_STROKE时，设置线段连接处样式，值有：Join.MITER（结合处为锐角）、Join.Round(结合处为圆弧)、Join.BEVEL(结合处为直线) 。
示例：public class MyView extends View {

private Paint mPaint;

public MyView(Context context) {
this(context, null, 0);
}
public MyView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public MyView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);

mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setColor(0xffff0000);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeWidth(20);
}

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

mPaint.setStrokeJoin(Paint.Join.MITER);
Path pathA = new Path();
pathA.moveTo(100,200);
pathA.lineTo(500,200);
pathA.lineTo(500,300);
canvas.drawPath(pathA, mPaint);

mPaint.setStrokeJoin(Paint.Join.ROUND);
Path pathB = new Path();
pathB.moveTo(100,500);
pathB.lineTo(500,500);
pathB.lineTo(500,600);
canvas.drawPath(pathB, mPaint);

mPaint.setStrokeJoin(Paint.Join.BEVEL);
Path pathC = new Path();
pathC.moveTo(100,800);
pathC.lineTo(500,800);
pathC.lineTo(500,900);
canvas.drawPath(pathC, mPaint);
}
}效果：

setPathEffect

setPathEffect(PathEffect effect);设置路径样式，其中传值是PathEffect的子类。其中已知子类有：CornerPathEffect、DashPathEffect、DiscretePathEffect、PathDashPathEffect、ComposePathEffect 和SumPathEffect。
CornerPathEffect（圆角效果）圆角效果就是拐角处变成圆形，CornerPathEffect(float radius)构造函数接收一个浮点值，它代表拐角处圆的半径。
DashPathEffect（虚线效果）虚线效果，DashPathEffect(float intervals[], float phase)构造函数接收两个值，第一个参数intervals[]表示组成虚线的一段线段的长度，然后根据此线段来作一个循环组成最终一整条线段。如：new float[] { 10, 5 };则表示虚线中，可见长度是10，间隔长度是5。intervals[]还有两个限制条件：长度必须大于等于2；个数必须是偶数。第二个参数phase表示开始绘制的偏移值，一般为0则可。
DiscretePathEffect（离散效果）离散效果就是将原来路径分隔成定长的线段，然后将每条线段随机偏移一段位置。DiscretePathEffect(float segmentLength, float deviation)构造函数接收两个值，第一个参数segmentLength表示将原来的路径切成多长的线段。第二个参数deviation表示被切成的每个小线段的可偏移距离。听起来是不是觉得很抽象?不用紧张，稍后看实例效果例会清晰了。
PathDashPathEffect（印章效果）印章效果就是用另一个路径图案作为印章，沿着线段路径像印章一样盖着连接。PathDashPathEffect(Path shape, float advance, float phase,Stylestyle)构造函数接收四个值，shape表示印章路径；advance表示两个印章之间的距离；phase表示绘制偏移距离；最后style表示遇到转角时的过度效果，值有：Style.ROTATE（旋转印章过渡转角）、Style.MORPH（变形印章过渡转角）和 Style.TRANSLATE（位移印章过渡转角）
ComposePathEffect（合并效果）和 SumPathEffect（叠加效果）合并效果是把两种样式合并成一种形式。而叠加效果则是直接的把两种样式放在一起。
 
示例：public class MyView extends View {

private Paint mPaint;

public MyView(Context context) {
this(context, null, 0);
}
public MyView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public MyView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);

mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setColor(0xffff0000);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeWidth(10);
}

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

// 圆角效果
mPaint.setPathEffect(new CornerPathEffect(100));
Path pathA = new Path();
pathA.moveTo(100,10);
pathA.lineTo(500,10);
pathA.lineTo(100,110);
canvas.drawPath(pathA, mPaint);

// 虚线效果
mPaint.setPathEffect(new DashPathEffect(new float[] { 20, 10 }, 0));
Path pathB = new Path();
pathB.moveTo(100,160);
pathB.lineTo(500,160);
pathB.lineTo(100,260);
canvas.drawPath(pathB, mPaint);

// 离散效果
mPaint.setPathEffect(new DiscretePathEffect(5, 10));
Path pathC = new Path();
pathC.moveTo(100,310);
pathC.lineTo(500,310);
pathC.lineTo(100,410);
canvas.drawPath(pathC, mPaint);

// 印章效果
Path stampPath = new Path();
stampPath.moveTo(0,20);
stampPath.lineTo(10,0);
stampPath.lineTo(20,20);
stampPath.close();
mPaint.setPathEffect(new PathDashPathEffect(stampPath, 20, 0, PathDashPathEffect.Style.TRANSLATE));
Path pathD = new Path();
pathD.moveTo(100,460);
pathD.lineTo(500,460);
pathD.lineTo(100,560);
canvas.drawPath(pathD, mPaint);

// 合并效果
mPaint.setPathEffect(new ComposePathEffect(new CornerPathEffect(100), new DashPathEffect(new float[] { 20, 10 }, 0)));
Path pathE = new Path();
pathE.moveTo(100,610);
pathE.lineTo(500,610);
pathE.lineTo(100,710);
canvas.drawPath(pathE, mPaint);

// 叠加效果
mPaint.setPathEffect(new SumPathEffect(new CornerPathEffect(100), new DashPathEffect(new float[] { 20, 10 }, 0)));
Path pathF = new Path();
pathF.moveTo(100,760);
pathF.lineTo(500,760);
pathF.lineTo(100,860);
canvas.drawPath(pathF, mPaint);
}
}效果：