AngledSweepGradient - Sweep gradient implementation for Compose with a customizable start angle

AngledSweepGradient.android.kt

import android.graphics.SweepGradient
import android.os.Build
import androidx.annotation.VisibleForTesting
import androidx.compose.runtime.Immutable
import androidx.compose.runtime.Stable
import androidx.compose.ui.geometry.*
import androidx.compose.ui.graphics.*
import androidx.compose.ui.util.fastForEachIndexed
import androidx.core.graphics.transform

@Stable
fun Brush.Companion.angledSweepGradient(
    vararg colorStops: Pair<Float, Color>,
    center: Offset = Offset.Unspecified,
    startAngle: Float = 0f
): Brush = AngledSweepGradient(
    colors = List(colorStops.size) { i -> colorStops[i].second },
    stops = List(colorStops.size) { i -> colorStops[i].first },
    center = center, startAngle = startAngle
)

@Stable
fun Brush.Companion.angledSweepGradient(
    colors: List<Color>,
    center: Offset = Offset.Unspecified,
    startAngle: Float = 0f
): Brush = AngledSweepGradient(
    colors = colors,
    stops = null,
    center = center,
    startAngle = startAngle
)


@Immutable
class AngledSweepGradient internal constructor(
    private val center: Offset,
    private val colors: List<Color>,
    private val stops: List<Float>? = null,
    private val startAngle: Float,
) : ShaderBrush() {

    override fun createShader(size: Size): Shader =
        AngledSweepGradientShader(
            if (center.isUnspecified) {
                size.center
            } else {
                Offset(
                    if (center.x == Float.POSITIVE_INFINITY) size.width else center.x,
                    if (center.y == Float.POSITIVE_INFINITY) size.height else center.y
                )
            },
            colors,
            stops,
            startAngle
        )

    override fun equals(other: Any?): Boolean {
        if (this === other) return true
        if (other !is AngledSweepGradient) return false

        if (center != other.center) return false
        if (colors != other.colors) return false
        if (stops != other.stops) return false
        if (startAngle != other.startAngle) return false

        return true
    }

    override fun hashCode(): Int {
        var result = center.hashCode()
        result = 31 * result + colors.hashCode()
        result = 31 * result + (stops?.hashCode() ?: 0)
        result = 31 * result + startAngle.hashCode()
        return result
    }

    override fun toString(): String {
        val centerValue = if (center.isSpecified) "center=$center, " else ""
        return "AngledSweepGradient(" +
                centerValue +
                "colors=$colors, stops=$stops, startAngle=$startAngle)"
    }
}

internal fun AngledSweepGradientShader(
    center: Offset,
    colors: List<Color>,
    colorStops: List<Float>?,
    startAngle: Float,
): Shader {
    validateColorStops(colors, colorStops)
    val numTransparentColors = countTransparentColors(colors)
    val shader = SweepGradient(
        center.x,
        center.y,
        makeTransparentColors(colors, numTransparentColors),
        makeTransparentStops(colorStops, colors, numTransparentColors)
    )
    shader.transform { setRotate(startAngle, center.x, center.y) }
    return shader
}

/*private fun List<Color>.toIntArray(): IntArray =
    IntArray(size) { i -> this[i].toArgb() }*/

private fun validateColorStops(colors: List<Color>, colorStops: List<Float>?) {
    if (colorStops == null) {
        if (colors.size < 2) {
            throw IllegalArgumentException(
                "colors must have length of at least 2 if colorStops " +
                        "is omitted."
            )
        }
    } else if (colors.size != colorStops.size) {
        throw IllegalArgumentException(
            "colors and colorStops arguments must have" +
                    " equal length."
        )
    }
}

@VisibleForTesting
internal fun countTransparentColors(colors: List<Color>): Int {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        return 0
    }
    var numTransparentColors = 0
    // Don't count the first and last value because we don't add stops for those
    for (i in 1 until colors.lastIndex) {
        if (colors[i].alpha == 0f) {
            numTransparentColors++
        }
    }
    return numTransparentColors
}

@VisibleForTesting
internal fun makeTransparentColors(
    colors: List<Color>,
    numTransparentColors: Int
): IntArray {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        // No change for Android O+, map the colors directly to their argb equivalent
        return IntArray(colors.size) { i -> colors[i].toArgb() }
    }
    val values = IntArray(colors.size + numTransparentColors)
    var valuesIndex = 0
    val lastIndex = colors.lastIndex
    colors.fastForEachIndexed { index, color ->
        if (color.alpha == 0f) {
            if (index == 0) {
                values[valuesIndex++] = colors[1].copy(alpha = 0f).toArgb()
            } else if (index == lastIndex) {
                values[valuesIndex++] = colors[index - 1].copy(alpha = 0f).toArgb()
            } else {
                val previousColor = colors[index - 1]
                values[valuesIndex++] = previousColor.copy(alpha = 0f).toArgb()

                val nextColor = colors[index + 1]
                values[valuesIndex++] = nextColor.copy(alpha = 0f).toArgb()
            }
        } else {
            values[valuesIndex++] = color.toArgb()
        }
    }
    return values
}

internal fun makeTransparentStops(
    stops: List<Float>?,
    colors: List<Color>,
    numTransparentColors: Int
): FloatArray? {
    if (numTransparentColors == 0) {
        return stops?.toFloatArray()
    }
    val newStops = FloatArray(colors.size + numTransparentColors)
    newStops[0] = stops?.get(0) ?: 0f
    var newStopsIndex = 1
    for (i in 1 until colors.lastIndex) {
        val color = colors[i]
        val stop = stops?.get(i) ?: i.toFloat() / colors.lastIndex
        newStops[newStopsIndex++] = stop
        if (color.alpha == 0f) {
            newStops[newStopsIndex++] = stop
        }
    }
    newStops[newStopsIndex] = stops?.get(colors.lastIndex) ?: 1f
    return newStops
}

AngledSweepGradient.desktop.kt

import androidx.compose.runtime.Immutable
import androidx.compose.runtime.Stable
import androidx.compose.ui.geometry.*
import androidx.compose.ui.graphics.*
import org.jetbrains.skia.FilterTileMode
import org.jetbrains.skia.GradientStyle

@Stable
fun Brush.Companion.angledSweepGradient(
    vararg colorStops: Pair<Float, Color>,
    center: Offset = Offset.Unspecified,
    startAngle: Float = 0f
): Brush = AngledSweepGradient(
    colors = List(colorStops.size) { i -> colorStops[i].second },
    stops = List(colorStops.size) { i -> colorStops[i].first },
    center = center, startAngle = startAngle
)

@Stable
fun Brush.Companion.angledSweepGradient(
    colors: List<Color>,
    center: Offset = Offset.Unspecified,
    startAngle: Float = 0f
): Brush = AngledSweepGradient(
    colors = colors,
    stops = null,
    center = center,
    startAngle = startAngle
)


@Immutable
class AngledSweepGradient internal constructor(
    private val center: Offset,
    private val colors: List<Color>,
    private val stops: List<Float>? = null,
    private val startAngle: Float,
) : ShaderBrush() {

    override fun createShader(size: Size): Shader =
        AngledSweepGradientShader(
            if (center.isUnspecified) {
                size.center
            } else {
                Offset(
                    if (center.x == Float.POSITIVE_INFINITY) size.width else center.x,
                    if (center.y == Float.POSITIVE_INFINITY) size.height else center.y
                )
            },
            colors,
            stops,
            startAngle
        )

    override fun equals(other: Any?): Boolean {
        if (this === other) return true
        if (other !is AngledSweepGradient) return false

        if (center != other.center) return false
        if (colors != other.colors) return false
        if (stops != other.stops) return false
        if (startAngle != other.startAngle) return false

        return true
    }

    override fun hashCode(): Int {
        var result = center.hashCode()
        result = 31 * result + colors.hashCode()
        result = 31 * result + (stops?.hashCode() ?: 0)
        result = 31 * result + startAngle.hashCode()
        return result
    }

    override fun toString(): String {
        val centerValue = if (center.isSpecified) "center=$center, " else ""
        return "AngledSweepGradient(" +
                centerValue +
                "colors=$colors, stops=$stops, startAngle=$startAngle)"
    }
}

internal fun AngledSweepGradientShader(
    center: Offset,
    colors: List<Color>,
    colorStops: List<Float>?,
    startAngle: Float,
): Shader {
    validateColorStops(colors, colorStops)
    return Shader.makeSweepGradient(
        x = center.x,
        y = center.y,
        startAngle = 0f + startAngle,
        endAngle = 360f + startAngle,
        colors = colors.toIntArray(),
        positions = colorStops?.toFloatArray(),
        style = GradientStyle.DEFAULT.withTileMode(FilterTileMode.REPEAT)
    )
}

private fun List<Color>.toIntArray(): IntArray =
    IntArray(size) { i -> this[i].toArgb() }

private fun validateColorStops(colors: List<Color>, colorStops: List<Float>?) {
    if (colorStops == null) {
        if (colors.size < 2) {
            throw IllegalArgumentException(
                "colors must have length of at least 2 if colorStops " +
                        "is omitted."
            )
        }
    } else if (colors.size != colorStops.size) {
        throw IllegalArgumentException(
            "colors and colorStops arguments must have" +
                    " equal length."
        )
    }
}