Canvas的Clip相关方法

Canvas这个类里面的方法类型不多,draw系列和clip系列，下面将写下clipRect()方法的不同参数的使用，以便日后参考。

用法示例

Rect rectA = new Rect(10, 10, 50, 50);
Rect rectB = new Rect(30, 30, 90, 90);
canvas.clipRect(rectA);
canvas.clipRect(rectB, Region.Op.XOR);

Region.Op说明

Op	Meanings
DIFFERENCE	A－B,{e\e∈A ∧ ¬(e∈B)}
INTERSECT	A ∩ B,{e\e∈A ∧ e∈B}
REPLACE	{e\e∈B}
REVERSE_DIFFERENCE	B－A,{e\e∈B ∧ ¬(e∈A)}
UNION	A ∪ B, {e\e∈A ∨ e∈B}
XOR	A△B: (A－B)∪(B－A)

效果图

clip.png

Demo代码

public class ClipView extends View {
    private int mLength;
    private Paint mPaint, mTextPaint;

    Rect rectOri, rectA, rectB;
    int divider = 10;
    String sA = "A", sB = "B";
    Region.Op[] ops;
    int tX, tY;

    public ClipView(Context context, AttributeSet attrs) {
        super(context, attrs);
        mPaint = new Paint();
        mTextPaint = new Paint();
        mTextPaint.setTextSize(20);
        mTextPaint.setAntiAlias(true);
        mTextPaint.setColor(Color.BLACK);
        rectOri = new Rect();
        rectA = new Rect();
        rectB = new Rect();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int width = getMeasuredWidth();
        mLength = (width - 4 * divider) / 3;
        rectOri.set(0, 0, mLength, mLength);
        rectA.set(10, 10, mLength / 2 + 20, mLength / 2 + 20);
        rectB.set(mLength / 2 - 20, mLength / 2 - 20, mLength - 10, mLength - 10);

        tX = 10;
        tY = mLength - 10;

        ops=Region.Op.values();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //draw origin view
        canvas.save();
        canvas.translate(divider, divider);
        mPaint.setColor(Color.WHITE);
        canvas.drawRect(rectOri, mPaint);
        mPaint.setColor(Color.GREEN);
        canvas.drawRect(rectA, mPaint);
        mPaint.setColor(Color.RED);
        canvas.drawRect(rectB, mPaint);

        // draw text
        canvas.drawText(sA, rectA.centerX(), rectA.centerY(), mTextPaint);
        canvas.drawText(sB, rectB.centerX(), rectB.centerY(), mTextPaint);
        canvas.drawText("Origin", tX, tY, mTextPaint);
        canvas.restore();

        //translate the canvas
        canvas.translate(0, mLength + divider);

        for (int i = 0; i < 6; i++) {
            //draw the compound view
            canvas.save();
            int dx = divider * (i % 3 + 1) + mLength * (i % 3);
            int dy = i > 2 ? (divider * 2 + mLength) : divider;
            canvas.translate(dx, dy);
            mPaint.setColor(Color.WHITE);
            canvas.drawRect(rectOri, mPaint);
            //draw text
            canvas.drawText(ops[i].name(), tX, tY, mTextPaint);
            //do clipping
            canvas.clipRect(rectA);
            canvas.clipRect(rectB, ops[i]);
            //draw all the area
            canvas.drawColor(Color.CYAN);
            canvas.restore();
        }
    }
}

Notice：

• 关闭硬件加速,不然部分机型和版本的系统无法正常工作
• 防止overdraw,可以多使用quickReject()和clip相关函数

Reference

• Canvas Api
• Canvas的clip函数详解
• Android的硬件加速及可能导致的问题