认识Canvas

1：认识Canvas
Canvas类简单理解就是表示一块画布,可以在上面画我们想画的东西
Canvas中的方法很多,Canvas可以绘制的对象有：
弧线(arcs) canvas.
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)
canvas.save()：把当前的绘制的图像保存起来，让后续的操作相当于是在一个新的图层上的操作。
canvas.restore(); 把当前画布返回（调整）到上一个save()状态之前
canvas.translate(dx, dy); //把当前画布的原点移到(dx,dy),后面的操作都以(dx,dy)作为参照点，默认原点为(0,0)
canvas.scale（x,y）;扩大。x为水平方向的放大倍数，y为竖直方向的放大倍数
canvas.rotate(angel):旋转.angle指旋转的角度，顺时针旋转。
canvas.transform():切变。所谓切变，其实就是把图像的顶部或底部推到一边。
canvas.saveLayer(bounds, paint, saveFlags);
推荐文章：http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2012/1212/703.html
2：Canvas 简单使用
有了上面对Canvas 方法的认识，那么下面我就用上面的方法来进行相关练习
/**
* Created by yishujun on 16/6/3.
*/
public class YView extends View {
    private Context mContext;
    //定义一个paint
    private Paint mPaint;
    public YView(Context context) {
        this(context, null);
    }
    public YView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }
    public YView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        this.mContext = context;
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        drawNomal(canvas);
        drawTest(canvas);
        //drawDial(canvas);
    }
    /**
     * 常规绘制  以(0,0)作为坐标原点参考点
     * @param canvas
     */
    private void drawNomal(Canvas canvas){
       mPaint =new Paint();
        // 绘制画布背景
        canvas.drawColor(Color.GRAY);
        //设置画笔颜色
        mPaint.setColor(Color.BLUE);
        //设置画笔为空心     如果将这里改为Style.STROKE  这个图中的实线圆柱体就变成了空心的圆柱体
        mPaint.setStyle(Paint.Style.STROKE);
        //绘制直线
        canvas.drawLine(50, 50, 450, 50, mPaint);
        //绘制矩形
        canvas.drawRect(100, 100, 200, 300, mPaint);
        //绘制矩形
        mPaint.setStyle(Paint.Style.FILL);
        canvas.drawRect(300, 100, 400, 400, mPaint);
        mPaint.setColor(Color.YELLOW);
        RectF r = new RectF(150, 500, 270, 600);
        // 画矩形
        canvas.drawRect(r, mPaint);
        // 画圆
        canvas.drawCircle(50, 500, 50, mPaint);
        RectF oval = new RectF(350, 500, 450, 700);
        // 画椭圆
        canvas.drawOval(oval, mPaint);
        RectF rect = new RectF(100, 700, 170, 800);
        // 画圆角矩形
        canvas.drawRoundRect(rect, 30, 20, mPaint);
        //绘制圆弧 绘制弧形
        mPaint.setStyle(Paint.Style.FILL);
        mPaint.setColor(Color.RED);
        RectF re1 = new RectF(1000, 50, 1400, 200);
        canvas.drawArc(re1, 10, 270, false, mPaint);
        RectF re2 = new RectF(1000, 300, 1400, 500);
        canvas.drawArc(re2, 10, 270, true, mPaint);
        //设置Path路径
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setColor(Color.GREEN);
        mPaint.setStrokeWidth(3);
        Path path = new Path();
        path.moveTo(500, 100);
        path.lineTo(920, 80);
        path.lineTo(720, 200);
        path.lineTo(600, 400);
        path.close();
        mPaint.setTextSize(46);
        canvas.drawPath(path, mPaint);
        canvas.drawTextOnPath("7qiuwoeruowoqjifasdkfjksjfiojio23ur8950", path, -20, -20, mPaint);
        //三角形
        path.moveTo(10, 330);
        path.lineTo(70, 330);
        path.lineTo(40, 270);
        path.close();
        canvas.drawPath(path, mPaint);
        //把开始的点和最后的点连接在一起，构成一个封闭梯形
        path.moveTo(10, 410);//绘画基点
        path.lineTo(70, 410);
        path.lineTo(55, 350);
        path.lineTo(25, 350);
        //如果是Style.FILL的话，不设置close,也没有区别，可是如果是STROKE模式， 如果不设置close,图形不封闭。当然，你也可以不设置close，再添加一条线，效果一样。
        path.close();
        canvas.drawPath(path, mPaint);
        //参数一为渐变起初点坐标x位置，参数二为y轴位置，参数三和四分辨对应渐变终点,其中参数new int[]{startColor, midleColor,endColor}是参与渐变效果的颜色集合，
        // 其中参数new float[]{0 , 0.5f, 1.0f}是定义每个颜色处于的渐变相对位置， 这个参数可以为null，如果为null表示所有的颜色按顺序均匀的分布
        // Shader.TileMode三种模式
        // REPEAT:沿着渐变方向循环重复
        // CLAMP:如果在预先定义的范围外画的话，就重复边界的颜色
        // MIRROR:与REPEAT一样都是循环重复，但这个会对称重复
        Shader mShader = new LinearGradient(0, 0, 100, 100,
                new int[]{Color.RED, Color.GREEN, Color.BLUE, Color.YELLOW},
                null, Shader.TileMode.REPEAT);
        mPaint.setShader(mShader);// 用Shader中定义定义的颜色来话
        mPaint.setStyle(Paint.Style.FILL);
        Path path1 = new Path();
        path1.moveTo(170, 410);
        path1.lineTo(230, 410);
        path1.lineTo(215, 350);
        path1.lineTo(185, 350);
        path1.close();
        canvas.drawPath(path1, mPaint);
        canvas.save();
    }

    /**
     * 绘制方法练习
     * @param canvas
     */
    private void drawTest(Canvas canvas){
        mPaint =new Paint();
        mPaint.setColor(Color.RED);
        //平移测试
        canvas.translate(50, 900);
        canvas.drawRect(new Rect(0, 0, 100, 100), mPaint);
        canvas.translate(50, 50);
        canvas.drawRect(new Rect(0, 0, 100, 100), mPaint);
        //缩放测试
        canvas.translate(100,-50);
        canvas.drawRect(new Rect(0, 0, 300, 300), mPaint);
        // 保存画布状态
        canvas.save();
        canvas.scale(0.5f, 0.5f);
        mPaint.setColor(Color.YELLOW);
        canvas.drawRect(new Rect(0, 0, 300, 300), mPaint);
        // 画布状态回滚
        canvas.restore();
        // 先将画布平移到矩形的中心
        canvas.translate(400, -50);
        canvas.drawRect(new Rect(0, 0, 300, 300), mPaint);
        //旋转测试
        canvas.save();
        canvas.translate(350, 50);
        canvas.drawRect(new Rect(0, 0, 200, 200), mPaint);
        mPaint.setColor(Color.RED);
        canvas.rotate(45,200,200);
        canvas.drawRect(new Rect(0, 0, 200, 200), mPaint);
        canvas.restore();
        //画布错切 三角函数tan的值
        canvas.translate(350, 300);
        canvas.drawRect(new Rect(0, 0, 400, 400), mPaint);
        // y 方向上倾斜45 度
        canvas.skew(0, 1);
        mPaint.setColor(0x8800ff00);
        canvas.drawRect(new Rect(0, 0, 400, 400), mPaint);
    }
}