How to draw a cutout or hole on the camera's opengl view?

I need to crop the camera view to a circle shape.

I tried using a surface view and overriding dispatchDraw(Canvas c), which worked. However it does not work when placed on top of another surface view.

So now I am using an OpenGlView and trying to figure out how to crop the display to a circle?

I assume this should be done with a filter, but I have no idea where to start.

[pedroSG94]

I assume that only preview should be circular right? In this case you need modify so much the library because filters are developed to apply in stream result and preview. I will try do a demo but I will not support it in the future.

[troy-lamerton]

I found a way to do it by setting the outline of the camera view to a circle. Turns out this method can be used to crop and view to a circle.

This is the Kotlin code I use to do it. Note that I crop a little extra to allow room for another view to show a border.

class CircleGlView : LightOpenGlView {

    constructor(context: Context) : super(context)
    constructor(context: Context, attrs: AttributeSet) : super(context, attrs)

    private val circleOutlineProvider = object : ViewOutlineProvider() {
        override fun getOutline(view: View, outline: Outline) {
            view.run {
//                val borderWidth = (height * borderWidthPercent)
                val outlineSize = (height * CIRCLE_PERCENT).toInt()
                val left = (width - outlineSize) / 2
                val top = (height - outlineSize) / 2

                outline.setOval(
                    left, top,
                    left + outlineSize, top + outlineSize
                )
            }
        }
    }

    init {
        outlineProvider = circleOutlineProvider
        clipToOutline = true
    }

    override fun getOutlineProvider(): ViewOutlineProvider {
        debug("getOutlineProvider !")
        return circleOutlineProvider
    }

    companion object {
        const val BORDER_PERCENT = 0.07f
        const val CIRCLE_PERCENT = 1f - BORDER_PERCENT
    }
}