skaldebane · October 27, 2025 13:02 · Oct 12, 2023 · Oct 12, 2023 · Oct 12, 2023 · Oct 12, 2023
diff --git a/AngledSweepGradient.android.kt b/AngledSweepGradient.android.kt
@@ -0,0 +1,191 @@
+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
+}
diff --git a/AngledSweepGradient.kt → AngledSweepGradient.desktop.kt b/AngledSweepGradient.kt → AngledSweepGradient.desktop.kt
diff --git a/AngledSweepGradient.kt b/AngledSweepGradient.kt
@@ -68,6 +68,7 @@ class AngledSweepGradient internal constructor(
         var result = center.hashCode()
         result = 31 * result + colors.hashCode()
         result = 31 * result + (stops?.hashCode() ?: 0)
+        result = 31 * result + startAngle.hashCode()
         return result
     }
 

diff --git a/AngledSweepGradient.kt b/AngledSweepGradient.kt
@@ -0,0 +1,117 @@
+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)
+        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."
+        )
+    }
+}
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