MyEffectPreviewView.kt

class MyEffectPreviewView : GLView {
    constructor(context: Context?) : super(context)
    constructor(context: Context?, attrs: AttributeSet?) : super(context, attrs)

    private var index = 0
    private var bitmaps: List<Bitmap> = emptyList()

    override fun onGLDraw(canvas: ICanvasGL) {
        val bitmaps = this.bitmaps
        val index = this.index

        bitmaps.getOrNull(index)?.let { bitmap ->
            canvas.drawBitmap(
                bitmap,
                0,
                0,
                bitmap.width,
                bitmap.height,
            )
        }

        this.index = if (bitmaps.isEmpty()) {
            0
        } else {
            (index + 1) % bitmaps.size
        }
    }

    fun setBitmaps(bitmaps: List<Bitmap>) {
        queueEvent {
            this.index = 0
            this.bitmaps = bitmaps
        }
    }
}