android - canvas 画线

refer to:  idcard lib的代码。　faceid库.

有个项目，需要用到身份证识别。

身份证识别的主窗口，需要一张背景图，加上边框。

所以，这个视图，需要用到canvas 来画图。

代码如下（注意代码中的注释，　包含了颜色说明，strokeWidth等)：

    @Override       // 复写这个方法。
    protected void onDraw(Canvas canvas) {       

        /**
         * 0X: 16进制颜色
         * FF: 透明度
         * 00D3FF:  hex颜色
         */
        /*
        int finderColor = 0XFF00D3FF;
        mDrawPaint.setStyle(Paint.Style.STROKE);　　// 设置样式，线是实心的。stoke: 描边。　fill: 填充
        mDrawPaint.setColor(finderColor);  // 设置颜色
        mDrawPaint.setStrokeWidth(3);    //边的宽度

       //  drawLine:  左，上，右，下四个边界.
        // 四个蓝色的角
        // left top
        canvas.drawLine(mShowRect.left, mShowRect.top, mShowRect.left + length, mShowRect.top, mDrawPaint);
        canvas.drawLine(mShowRect.left, mShowRect.top, mShowRect.left, mShowRect.top + length, mDrawPaint);

        // right top
        canvas.drawLine(mShowRect.right, mShowRect.top, mShowRect.right - length, mShowRect.top, mDrawPaint);
        canvas.drawLine(mShowRect.right, mShowRect.top, mShowRect.right, mShowRect.top + length, mDrawPaint);

        // left bottom
        canvas.drawLine(mShowRect.left, mShowRect.bottom, mShowRect.left + length, mShowRect.bottom, mDrawPaint);
        canvas.drawLine(mShowRect.left, mShowRect.bottom, mShowRect.left, mShowRect.bottom - length, mDrawPaint);

        // right bottom
        canvas.drawLine(mShowRect.right, mShowRect.bottom, mShowRect.right - length, mShowRect.bottom, mDrawPaint);
        canvas.drawLine(mShowRect.right, mShowRect.bottom, mShowRect.right, mShowRect.bottom - length, mDrawPaint);
    }