ui: OKLCH colors for gradients in onboarding cards (#6859)

* ui: OKLCH colors for gradients in onboarding cards

* add wide gamut to manifest

apps/multiplatform/common/src/commonMain/kotlin/chat/simplex/common/ui/theme/Color.kt

@@ -3,16 +3,64 @@ package chat.simplex.common.ui.theme
 import androidx.compose.material.LocalContentColor
 import androidx.compose.material.MaterialTheme
 import androidx.compose.runtime.Composable
-import androidx.compose.runtime.collectAsState
 import androidx.compose.ui.graphics.*
-import chat.simplex.common.views.helpers.mixWith
+import androidx.compose.ui.graphics.colorspace.ColorSpaces
+import kotlin.math.cos
+import kotlin.math.max
 import kotlin.math.min
+import kotlin.math.pow
+import kotlin.math.sin
+
+fun oklch(L: Float, C: Float, H: Float, alpha: Float = 1f): Color {
+  val hRad = H * (Math.PI.toFloat() / 180f)
+  val cosH = cos(hRad)
+  val sinH = sin(hRad)
+
+  fun linearP3(c: Float): Triple<Float, Float, Float> {
+    val a = c * cosH
+    val b = c * sinH
+    // oklab → LMS (Ottosson 2021)
+    val l_ = L + 0.3963377774f * a + 0.2158037573f * b
+    val m_ = L - 0.1055613458f * a - 0.0638541728f * b
+    val s_ = L - 0.0894841775f * a - 1.2914855480f * b
+    val l = l_ * l_ * l_
+    val m = m_ * m_ * m_
+    val s = s_ * s_ * s_
+    // LMS → linear Display P3
+    return Triple(
+      3.1281105148f * l - 2.2570749853f * m + 0.1293047593f * s,
+      -1.0911282009f * l + 2.4132668169f * m - 0.3221681599f * s,
+      -0.0260136845f * l - 0.5080276339f * m + 1.5333166364f * s
+    )
+  }
+
+  fun inGamut(r: Float, g: Float, b: Float) = r in 0f..1f && g in 0f..1f && b in 0f..1f
+
+  // linear P3 → gamma-encoded P3 (same transfer function as sRGB)
+  fun gammaEncode(x: Float): Float =
+    if (x >= 0.0031308f) 1.055f * min(x, 1f).pow(1f / 2.4f) - 0.055f
+    else 12.92f * max(x, 0f)
+
+  var (r, g, b) = linearP3(C)
+  if (!inGamut(r, g, b)) {
+    var lo = 0f; var hi = C
+    while (hi - lo > 1e-5f) {
+      val mid = (lo + hi) / 2
+      val (mr, mg, mb) = linearP3(mid)
+      if (inGamut(mr, mg, mb)) { lo = mid; r = mr; g = mg; b = mb }
+      else hi = mid
+    }
+  }
+
+  return Color(
+    red = gammaEncode(r),
+    green = gammaEncode(g),
+    blue = gammaEncode(b),
+    alpha = alpha,
+    colorSpace = ColorSpaces.DisplayP3
+  )
+}
 
-val Purple200 = Color(0xFFBB86FC)
-val Purple500 = Color(0xFF6200EE)
-val Purple700 = Color(0xFF3700B3)
-val Teal200 = Color(0xFF03DAC5)
-val Gray = Color(0x22222222)
 val Indigo = Color(0xFF9966FF)
 val SimplexBlue = Color(0, 136, 255, 255)  // If this value changes also need to update #0088ff in string resource files
 val SimplexGreen = Color(77, 218, 103, 255)

apps/multiplatform/common/src/commonMain/kotlin/chat/simplex/common/views/newchat/OnboardingCards.kt

@@ -89,17 +89,17 @@ internal fun gradientPoints(aspectRatio: Float, scale: Float): GradientEndpoints
 }
 
 internal val lightStops = arrayOf(
-  0.0f to Color(0xFFd2e8ff),
-  0.5f to Color(0xFFcce9ff),
-  0.9f to Color(0xFFdfffff),
-  1.0f to Color(0xFFfffcea)
+  0.0f to oklch(0.9219f, 0.0431f, 249.4f),
+  0.5f to oklch(0.9198f, 0.0471f, 240.7f),
+  0.9f to oklch(0.9772f, 0.0358f, 196.6f),
+  1.0f to oklch(0.9886f, 0.0272f, 99.1f)
 )
 
 internal val darkStops = arrayOf(
-  0.4f to Color(0xFF040a24),
-  0.72f to Color(0xFF3854ab),
-  0.9f to Color(0xFFa8edf3),
-  1.0f to Color(0xFFfff6e0)
+  0.4f to oklch(0.1578f, 0.0609f, 267.3f),
+  0.72f to oklch(0.4729f, 0.1574f, 267.3f),
+  0.9f to oklch(0.9024f, 0.0760f, 202.8f),
+  1.0f to oklch(0.9744f, 0.0370f, 88.4f)
 )
 
 private fun Modifier.maxHeightByWidthRatio(ratio: Float) = layout { measurable, constraints ->