example of how to rotate sweep gradient in android view

RotatingGradientView.kt

/**
 * View showing rotating SweepGradient.
 */
class RotatingGradientView @JvmOverloads constructor(
    context: Context?,
    attrs: AttributeSet? = null,
    defStyleAttr: Int = 0
) : View(context, attrs, defStyleAttr) {
    private val paint = Paint(Paint.ANTI_ALIAS_FLAG)
    private var middleX = 0f
    private var middleY = 0f
    private var gradientMatrix = Matrix()
    private var rotationAnimator = ValueAnimator.ofFloat(0f, 1f)
    private var gradient: SweepGradient? = null

    init {
        paint.apply {
            style = Paint.Style.STROKE
            strokeWidth = resources.getDimension(R.dimen.space_small)
        }
        rotationAnimator.apply {
            addUpdateListener {
                gradientMatrix.postRotate(-ROTATION_ANGLE, middleX, middleY)
                gradient?.setLocalMatrix(gradientMatrix)
                invalidate()
            }
            duration = ANIMATION_DURATION_MS
            repeatCount = ValueAnimator.INFINITE
            repeatMode = ValueAnimator.RESTART
            interpolator = LinearInterpolator()
        }
    }

    override fun onSizeChanged(w: Int, h: Int, oldw: Int, oldh: Int) {
        super.onSizeChanged(w, h, oldw, oldh)
        middleX = w / 2f
        middleY = h / 2f
        val colorWhite = ContextCompat.getColor(context, R.color.color_light)
        val colorDark = ContextCompat.getColor(context, R.color.color_dark)
        gradient = SweepGradient(middleX, middleY, colorDark, colorWhite).apply {
            setLocalMatrix(gradientMatrix)
        }
        paint.shader = gradient
        rotationAnimator.start()
    }

    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)
        // draw a shape
        val width = measuredWidth
        val height = measuredHeight
       
        val strokeWidth = paint.strokeWidth
        canvas.drawLine(
            0f, height * 0.07f + strokeWidth, width / 2f,
            strokeWidth / 2f, paint
        )
        canvas.drawLine(width / 2f, strokeWidth / 2f, width.toFloat(), height * 0.07f + strokeWidth, paint)

        canvas.drawLine(
            width - strokeWidth / 2f, height * 0.1f + strokeWidth,
            width - strokeWidth / 2f, height * 0.66f - strokeWidth, paint
        )
        canvas.drawLine(
            strokeWidth / 2f, height * 0.1f + strokeWidth, strokeWidth / 2f,
            height * 0.66f - strokeWidth, paint
        )

        canvas.drawLine(
            width.toFloat(), height * 0.66f - strokeWidth, width / 2f,
            height - strokeWidth, paint
        )
        canvas.drawLine(
            0f, height * 0.66f - strokeWidth, width / 2f,
            height - strokeWidth, paint
        )
    }

    override fun onDetachedFromWindow() {
        rotationAnimator.cancel()
        super.onDetachedFromWindow()
    }

    companion object {
        private const val ROTATION_ANGLE = 5f
        private const val ANIMATION_DURATION_MS = 1000L
    }
    
}