二十二、Android绘图基础Canvas、Paint等

Canvas

重新onDraw(Canvas canvas)方法时涉及绘图API ：Canvas
Canvas绘制方法

drawArc(RectF oval, float startAngle, float sweepAngle, boolean useCenter, Paint paint
//绘制弧

drawBitmap(Bitmap bitmap,Rect src, Rect dst,Paint paint)
//在指定点绘制从源位图中“挖取”的一块

drawBitmap(Bitmap bitmap, float left, float top, Paint paint)
//在指定点绘制位图

drawCircle(float cx, float cy, float radius, Paint paint)
//在指定点绘制一个圆

drawLine(float startX, float startY, float stopX, float stopY, Paint paint)
//绘制一条线

drawLines(float[] pts, int offset, int count, Paint paint)
//绘制多条线

drawOval(RectF oval, Paint paint)
//绘制椭圆

drawPath(Path path, Paint paint)
//沿着指定Path绘制任意形状

drawPoint(float x, float y, Paint paint)
//绘制一个点

drawPoints(float[] pts, int offset, int count, Paint paint)
//绘制多个点

drawRect(float left, float top, float right, float bottom, Paint paint)
//绘制一个矩形

drawRoundRect(RectF rect, float rx, float ry, Paint paint)
//绘制一个圆角矩形

drawText(String text, float x, float y, Paint paint)
//绘制字符串

drawTextOnPath(char[] text, int index, int count, Path path, float hOffset, float vOffset, Paint paint)
//沿着路径绘制字符串

clipRect(float left, float top, float right, float bottom)
//剪切一个矩形区域

除上表定义的方法以外，Canvas还提供如下方法：
1.rotate(float degrees, float px, float py)对Canvas旋转
2.scale(float sx, float sy, float px, float py)对Canvas放缩
3.translate(float dx, float dy)对Canvas移动。dx为X轴方向移动，dy为Y轴方向移动。

Paint 画笔

setARGB();/setColor();//设置颜色

setAlpha(int a) //设置透明度

setAntiAlias(boolean aa) //设置是否抗锯齿

setColor(int color)//设置颜色

setPathEffect(PathEffect effect)//设置绘制路径是路径效果

setShader(Shader shader)//设置画笔填充效果

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

setStrokeWidth(float width)//设置画笔触宽度

setStrokeJoin(Paint.Join join)//设置画笔转弯处的连接风格

setStyle(Paint.Style style)//设置Paint的填充风格

setTextAlign(Paint.Align align)//设置绘制文本时的文字对齐方式

setTextSize(float textSize)//设置绘制文本时的文字大小

PathEffect 类

PathEffect为路径提供不同效果，包含如下子类：
1.ComposePathEffect
2.CornerPathEffect
3.DashPathEffect
4.DiscretePathEffect
5.PathDashPathEffect
6.SumPathEffect

例子：

    float phase;

    PathEffect[] effects = new PathEffect[7];

    int[] colors;

    private Paint paint;

    Path path;

    public MyView(Context context) {
        super(context);
        init();
    }

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

    public MyView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init(){
        paint = new Paint();
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(4);
        //创建Path
        path = new Path();
        path.moveTo(0,0);
        for(int i = 1; i <= 15; i++){
            path.lineTo(i*20, (float)(Math.random() * 100));
        }
        colors = new int[]{
                Color.BLACK, Color.BLUE, Color.CYAN, Color.GREEN, Color.MAGENTA,
                Color.RED, Color.YELLOW
        };
    }

    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawColor(Color.WHITE);//白色背景
        //七种路径效果
        effects[0] = null;
        effects[1] = new CornerPathEffect(10);
        effects[2] = new DiscretePathEffect(3.0f, 5.0f);
        effects[3] = new DashPathEffect(new float[]{20,10,5,10}, phase);
        Path p = new Path();
        p.addRect(0, 0, 8, 8, Path.Direction.CCW);
        effects[4] = new PathDashPathEffect(p, 12, phase, PathDashPathEffect.Style.ROTATE);
        effects[5] = new ComposePathEffect(effects[2], effects[4]);
        effects[6] = new SumPathEffect(effects[4], effects[3]);
        canvas.translate(8,8);
        for(int i = 0; i < effects.length; i++){
            paint.setPathEffect(effects[i]);
            paint.setColor(colors[i]);
            canvas.drawPath(path, paint);
            canvas.translate(0,100);
        }
        phase += 1;
        invalidate();
    }

效果如图：