小知识，大挑战！本文正在参与“程序员必备小知识”创作活动。

前言

生活中绘制图案需要纸和笔，android中提供了类似的工具Canvas和Paint，分别对应画布和画笔。

The Paint class holds the style and color information about how to draw geometries, text and bitmaps.

Paint拥有绘制几何图形、文本、图片的样式和颜色信息。

The Canvas class holds the "draw" calls. To draw something, you need 4 basic components: A Bitmap to hold the pixels, a Canvas to host the draw calls (writing into the bitmap), a drawing primitive (e.g. Rect, Path, text, Bitmap), and a paint (to describe the colors and styles for the drawing).

Canvas拥有绘图的请求权，想要完成绘制，需要4个基本元素：保存像素的Bitmap、一个可以调用draw方法的canvas、要绘制的内容描述、一个画笔。凭借这4个元素就可以绘制到一个bitmap上，然后渲染到屏幕上。

1.简介

今天先将一下Paint的相关内容。

Paint提供了三种初始化方法：

Paint()
Paint(int flag)
Paint(Paint paint)

2.基本属性使用

2.1 setAlpha透明度

setAlpha(int a) 设置范围0~255

2.2 setStyle填充样式

填充样式表示绘线和填充的选择：

Paint.Style.FILL
Paint.Style.FILL_AND_STROKE
Paint.Style.STROKE

2.3 颜色，字体，对齐，抗锯齿

setColor，setARGB设置颜色，设置画笔的颜色，

setARGB（）参数范围0-255。
setAntiAlias（boolean）抗锯齿，使边界更顺滑（有些屏幕分辨率不高，导致像素点比较大，绘制边界可能会有颗粒感，打开抗锯齿边界颗粒感会减少）。

setTextSize(float textSize) 字体大小，单位是px，如果是dp要注意转换。
setTextAlign(Paint.Align.RIGHT)设置字体对齐方式，根据下面的实例可以，对齐方式基于开始绘制的点。

mTextPaint.setTextAlign(Paint.Align.LEFT);
canvas.drawText("MatumbaMan的博客",200, 200, mTextPaint);

mTextPaint.setTextAlign(Paint.Align.RIGHT);
canvas.drawText("MatumbaMan的博客",200, 300, mTextPaint);

mTextPaint.setTextAlign(Paint.Align.CENTER);
canvas.drawText("MatumbaMan的博客",200, 400, mTextPaint);

2.4 setShadowLayer 阴影

setShadowLayer(float radius, float dx, float dy, int shadowColor) 设置阴影

Radius设置角度，dx，dy控制字体的上下左右出现，有正负之分，dx的正负代表右左，dy的正负代表下上。

mTextPaint.setTextAlign(Paint.Align.LEFT);
mTextPaint.setShadowLayer(10, -20, 40, Color.GRAY);
canvas.drawText("MatumbaMan的博客",200, 200, mTextPaint);


mTextPaint.setTextAlign(Paint.Align.RIGHT);
canvas.drawText("MatumbaMan的博客",200, 300, mTextPaint);

mTextPaint.setTextAlign(Paint.Align.CENTER);
canvas.drawText("MatumbaMan的博客",200, 400, mTextPaint);

2.5 setStrokeCap

setStrokeCap(Paint.Cap.ROUND)
设置绘制起始点和结尾点的样式，
三种样式ROUND,BUTT,SQUARE\

Cap.ROUND(圆形)
Cap.SQUARE(方形)
Paint.Cap.BUTT(无)

Path path = new Path();
path.moveTo(100, 100);
path.lineTo(100, 200);
path.lineTo(200, 300);
canvas.drawPath(path, mPaint2);//无

path.reset();
path.moveTo(300, 100);
path.lineTo(300, 200);
path.lineTo(400, 300);
mPaint2.setStrokeCap(Paint.Cap.ROUND);//圆
canvas.drawPath(path, mPaint2);

path.reset();
path.moveTo(500, 100);
path.lineTo(500, 200);
path.lineTo(600, 300);
mPaint2.setStrokeCap(Paint.Cap.SQUARE);//方
canvas.drawPath(path, mPaint2);

2.6 setStrokeJoin

setStrokeJoin(Paint.Join join)，设置绘制path连接点的样式

Join.MITER（结合处为锐角）
Join.Round(结合处为圆弧)
Join.BEVEL(结合处为直线)

Path path = new Path();
path.moveTo(100, 100);
path.lineTo(100, 200);
path.lineTo(200, 300);
mPaint2.setStrokeJoin(Paint.Join.MITER);
canvas.drawPath(path, mPaint2);

path.reset();
path.moveTo(300, 100);
path.lineTo(300, 200);
path.lineTo(400, 300);
mPaint2.setStrokeJoin(Paint.Join.ROUND);
canvas.drawPath(path, mPaint2);

path.reset();
path.moveTo(500, 100);
path.lineTo(500, 200);
path.lineTo(600, 300);
mPaint2.setStrokeJoin(Paint.Join.BEVEL);
canvas.drawPath(path, mPaint2);

Android原生绘图（一）：Paint

前言