I need to draw in canvas four boundary corner for qr code scanner. Here is example (I need to draw this four blue boundary corner).

I know how to draw rectangle:

 val rectF = RectF(left, top, right, bottom)
            canvas.drawRoundRect(rectF, radius, radius, paint)

But it is possible to draw only for boundary corners (without edge).

Please, help me.

CodePudding user response：

One way is just to draw eight lines in the right pattern

val lengthF = 100.0f // Length of stand out from corners

canvas.drawLine(left,top, left   lengthF, top, paint) // Top Left to right
canvas.drawLine(left,top, left, top   lengthF, paint) // Top Left to bottom
canvas.drawLine(right,top, right - lengthF, top, paint) // Top Right to left
canvas.drawLine(right,top, right, top   lengthF, paint) // Top Right to Bottom
canvas.drawLine(left,bottom, left   lengthF, bottom, paint) // Bottom Left to right
canvas.drawLine(left,bottom, left, bottom - lengthF, paint) // Bottom Left to top
canvas.drawLine(right,bottom, right - lengthF, bottom, paint) // Bottom right to left
canvas.drawLine(right,bottom, right, bottom - lengthF, paint) // Bottom right to top

Update for rounded corners keeping it to API level 1

val paint = Paint();
paint.setColor(Color.BLACK);
paint.setStrokeWidth(3);
paint.setStyle(Paint.Style.STROKE);
paint.setAntiAlias(true);

val lengthF = 40.0f; // Standout of straight part
val radius = 20f;

canvas.drawLine(left   radius, top, left   lengthF, top, paint) // Top Left to right
canvas.drawLine(left,top   radius, left, top   lengthF, paint) // Top Left to bottom
val rectTL = RectF(left,top, left   (radius*2), top   (radius*2))
canvas.drawArc(rectTL,180f, 90f, false, paint);

canvas.drawLine(right - radius,top, right - lengthF, top, paint); // Top Right to left
canvas.drawLine(right,top   radius, right, top   lengthF, paint); // Top Right to Bottom
val rectTR = RectF(right - (radius*2),top, right, top   (radius*2));
canvas.drawArc(rectTR,270f, 90f, false, paint);

canvas.drawLine(left   radius,bottom, left   lengthF, bottom, paint); // Bottom Left to right
canvas.drawLine(left,bottom - radius, left, bottom - lengthF, paint); // Bottom Left to top
val rectBL = RectF(left,bottom - (radius*2), left   (radius*2), bottom);
canvas.drawArc(rectBL,90f, 90f, false, paint);

canvas.drawLine(right - radius,bottom, right - lengthF, bottom, paint); // Bottom right to left
canvas.drawLine(right,bottom - radius, right, bottom - lengthF, paint); // Bottom right to top
val rectBR = RectF(right - (radius*2),bottom - (radius*2), right, bottom);
canvas.drawArc(rectBR,0f, 90f, false, paint);

Can do similar with a Path

CodePudding user response：

You can achieve it by simply using the drawPath() method of Canvas ::

Use the below method to draw boundaries with rounded corners :

fun drawBoundaries(canvas: Canvas) {

    val paint = Paint()
    paint.color = Color.RED
    paint.style = Paint.Style.STROKE
    paint.strokeWidth = 20f
    paint.isAntiAlias = true

    // Adjust according to your requirements..
    val length = canvas.width * 0.25f
    val corner = length * 0.25f
    val left = 50f
    val top = 50f
    val right = canvas.width - 50f
    val bottom = canvas.height - 50f

    val path = Path()

    // Top-Left corner..
    path.moveTo(left, top   length)
    path.lineTo(left, top   corner)
    path.cubicTo(left, top   corner, left, top, left   corner, top)
    path.lineTo(left   length, top)

    // Top-Right corner..
    path.moveTo(right - length, top)
    path.lineTo(right - corner, top)
    path.cubicTo(right - corner, top, right, top, right, top   corner)
    path.lineTo(right, top   length)

    // Bottom-Right corner..
    path.moveTo(right, bottom - length)
    path.lineTo(right, bottom - corner)
    path.cubicTo(right, bottom - corner, right, bottom, right - corner, bottom)
    path.lineTo(right - length, bottom)

    // Bottom-Left corner..
    path.moveTo(left   length, bottom)
    path.lineTo(left   corner, bottom)
    path.cubicTo(left   corner, bottom, left, bottom, left, bottom - corner)
    path.lineTo(left, bottom - length)

    // Draw path..
    canvas.drawPath(path, paint)
}