cavas的用法

变换操作

public class TransformView extends View {

    private Paint mPaint;

    public TransformView(Context context) {
        this(context, null);
    }

    public TransformView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

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

    private void init() {
        mPaint = new Paint();
        mPaint.setColor(Color.RED);
        mPaint.setStrokeWidth(4);
        mPaint.setStyle(Paint.Style.STROKE);
    }

    @RequiresApi(api = Build.VERSION_CODES.O)
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

//        //1，平移操作
//        canvas.drawRect(0,0, 400, 400, mPaint);
//        canvas.translate(50, 50);
//        mPaint.setColor(Color.GRAY);
//        canvas.drawRect(0,0, 400, 400, mPaint);
//        canvas.drawLine(0, 0, 600,600, mPaint);

//        //缩放操纵
//        canvas.drawRect(200,200, 700,700, mPaint);
//        canvas.scale(0.5f, 0.5f);
        //先translate(px, py),再scale(sx, sy),再反响translate
//        canvas.scale(0.5f, 0.5f, 200,200);

//        canvas.translate(200, 200);
//        canvas.scale(0.5f, 0.5f);
//        canvas.translate(-200, -200);

//        mPaint.setColor(Color.GRAY);
//        canvas.drawRect(200,200, 700,700, mPaint);
//        canvas.drawLine(0,0, 400, 600, mPaint);

        //旋转操作
//        canvas.translate(50,50);
//        canvas.drawRect(0,0, 700,700, mPaint);
//        canvas.rotate(45);
//        mPaint.setColor(Color.GRAY);
//        canvas.drawRect(0,0, 700,700, mPaint);

//        canvas.drawRect(400, 400, 900, 900, mPaint);
//        canvas.rotate(45, 650, 650); //px, py表示旋转中心的坐标
//        mPaint.setColor(Color.GRAY);
//        canvas.drawRect(400, 400, 900, 900, mPaint);

        //倾斜操作
//        canvas.drawRect(0,0, 400, 400, mPaint);
////        canvas.skew(1, 0); //在X方向倾斜45度,Y轴逆时针旋转45
//        canvas.skew(0, 1); //在y方向倾斜45度， X轴顺时针旋转45
//        mPaint.setColor(Color.GRAY);
//        canvas.drawRect(0, 0, 400, 400, mPaint);

        //切割
//        canvas.drawRect(200, 200,700, 700, mPaint);
//        mPaint.setColor(Color.GRAY);
//        canvas.drawRect(200, 800,700, 1300, mPaint);
//        canvas.clipRect(200, 200,700, 700); //画布被裁剪
//        canvas.drawCircle(100,100, 100,mPaint); //坐标超出裁剪区域，无法绘制
//        canvas.drawCircle(300, 300, 100, mPaint); //坐标区域在裁剪范围内，绘制成功

        //反向切割
//        canvas.drawRect(200, 200,700, 700, mPaint);
//        mPaint.setColor(Color.GRAY);
//        canvas.drawRect(200, 800,700, 1300, mPaint);
//        canvas.clipOutRect(200,200,700,700); //画布裁剪外的区域
//        canvas.drawCircle(100,100,100,mPaint); //坐标区域在裁剪范围内，绘制成功
//        canvas.drawCircle(300, 300, 100, mPaint);//坐标超出裁剪区域，无法绘制

        //矩阵
        canvas.drawRect(0,0,700,700, mPaint);
        Matrix matrix = new Matrix();
        matrix.setTranslate(100,100);
        matrix.setRotate(45);
        matrix.setScale(0.5f, 0.5f);
        canvas.setMatrix(matrix);
        mPaint.setColor(Color.GRAY);
        canvas.drawRect(0,0,700,700, mPaint);

    }

}

状态保存和恢复

public class SaveRestoreView extends View {

    private Paint mPaint;

    public SaveRestoreView(Context context) {
        this(context, null);
    }

    public SaveRestoreView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

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

    private void init() {
        mPaint = new Paint();
        mPaint.setColor(Color.RED);
        mPaint.setStrokeWidth(4);
        mPaint.setStyle(Paint.Style.STROKE);
    }

    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        /**
         * 1.canvas内部对于状态的保存存放在栈中
         * 2.可以多次调用save保存canvas的状态，并且可以通过getSaveCount方法获取保存的状态个数
         * 3.可以通过restore方法返回最近一次save前的状态，也可以通过restoreToCount返回指定save状态。指定save状态之后的状态全部被清除
         * 4.saveLayer可以创建新的图层，之后的绘制都会在这个图层之上绘制，直到调用restore方法
         * 注意：绘制的坐标系不能超过图层的范围， saveLayerAlpha对图层增加了透明度信息
         */

//        Log.e("", "onDraw: "+canvas.getSaveCount());
//        canvas.drawRect(200, 200, 700, 700, mPaint);
//        int state = canvas.save();
//        Log.e("", "onDraw: "+canvas.getSaveCount());
//        canvas.translate(50,50);
//
//        mPaint.setColor(Color.GRAY);
//        canvas.drawRect(0,0,500,500, mPaint);
//
//        canvas.save();
//        Log.e("", "onDraw: "+canvas.getSaveCount());
//        canvas.translate(50,50);
//        mPaint.setColor(Color.BLUE);
//        canvas.drawRect(0,0,500,500, mPaint);
//
//
////        canvas.restore();
//        Log.e("", "onDraw: "+canvas.getSaveCount());
////        canvas.restore();
//        canvas.restoreToCount(state);
//
////        canvas.restore();
//        Log.e("", "onDraw: "+canvas.getSaveCount());
//        canvas.drawLine(0,0, 400,500, mPaint);

        canvas.drawRect(200,200, 700,700, mPaint);

        int layerId = canvas.saveLayer(0,0, 700, 700, mPaint);
        mPaint.setColor(Color.GRAY);
        Matrix matrix = new Matrix();
        matrix.setTranslate(100,100);
        canvas.setMatrix(matrix);
        canvas.drawRect(0,0,700,700, mPaint); //由于平移操作，导致绘制的矩形超出了图层的大小，所以绘制不完全
        canvas.restoreToCount(layerId);

        mPaint.setColor(Color.RED);
        canvas.drawRect(0,0,100,100, mPaint);

    }
}