From 815f6c2b2571020faa1e56381d8ff1c0596bd655 Mon Sep 17 00:00:00 2001
From: Tangem <git@tangem.com>
Date: Fri, 31 Jul 2026 16:36:46 +0300
Subject: [PATCH] Updated on 2026-08-14

---
 .../core/ui/ds2/surface/TangemSurface.kt      | 24 +++++++++++--
 .../com/tangem/core/ui/extensions/Shadow.kt   | 35 ++++++++++++++++---
 2 files changed, 52 insertions(+), 7 deletions(-)

diff --git a/core/ui/src/main/java/com/tangem/core/ui/ds2/surface/TangemSurface.kt b/core/ui/src/main/java/com/tangem/core/ui/ds2/surface/TangemSurface.kt
index 9cab348f29..8cf038d8d0 100644
--- a/core/ui/src/main/java/com/tangem/core/ui/ds2/surface/TangemSurface.kt
+++ b/core/ui/src/main/java/com/tangem/core/ui/ds2/surface/TangemSurface.kt
@@ -26,6 +26,7 @@ import com.tangem.core.ui.components.haze.hazeEffectTangem
 import com.tangem.core.ui.extensions.conditionalCompose
 import com.tangem.core.ui.extensions.softLayerShadow
 import com.tangem.core.ui.res.LocalHazeState
+import com.tangem.core.ui.res.LocalRootBackgroundColor
 import com.tangem.core.ui.res.TangemTheme
 import dev.chrisbanes.haze.HazeStyle
 import dev.chrisbanes.haze.HazeTint
@@ -38,7 +39,8 @@ import dev.chrisbanes.haze.HazeTint
  * Rendering modes:
  * - **Flat** (`isMaterial = false`, default): a solid [color] background clipped to [shape].
  * - **Material** (`isMaterial = true`): the [color] parameter is ignored. The surface adds a soft
- *   drop shadow and a gradient stroke (`material.border`), then renders a haze-blurred backdrop
+ *   drop shadow (omitted on dark backdrops, where it is not representable in 8 bits and would show
+ *   as a banding ring) and a gradient stroke (`material.border`), then renders a haze-blurred backdrop
  *   tinted with `material.fill.blur`. When `LocalHazeState.blurEnabled` is `false` (e.g.
  *   previews, low-end devices), the surface falls back to opaque `material.fill.solid` overlaid
  *   with translucent `material.tint.solid` so both layers remain visible.
@@ -57,6 +59,8 @@ import dev.chrisbanes.haze.HazeTint
  * @param onClick Click handler. `null` makes the surface non-interactive.
  * @param enabled Forwarded to the click handler.
 
+ * @param shadowRadius Blur size of the material drop shadow, expressed as a Figma `box-shadow`
+ *   blur. Ignored when [isMaterial] is `false`.
  * @param content Content rendered inside the clipped surface.
  */
 @Suppress("UnsafeCallOnNullableType", "")
@@ -118,10 +122,15 @@ fun TangemSurface(
  */
 @Composable
 private fun Modifier.materialShadow(shape: Shape, radius: Dp): Modifier {
+    // Approximates the backdrop: a material surface sitting on a non-root background keeps the
+    // root's verdict, which is accurate enough since only near-black backgrounds are rejected.
+    val backdrop by LocalRootBackgroundColor.current
+    if (!backdrop.canRenderShadow(MATERIAL_SHADOW_ALPHA)) return this
+
     val isBlurEnabled = LocalHazeState.current.blurEnabled
     return softLayerShadow(
         radius = radius,
-        color = Color.Black.copy(alpha = 0.12f),
+        color = Color.Black.copy(alpha = MATERIAL_SHADOW_ALPHA),
         shape = shape,
         spread = 0.dp,
         offset = DpOffset(x = 0.dp, y = 8.dp),
@@ -129,6 +138,17 @@ private fun Modifier.materialShadow(shape: Shape, radius: Dp): Modifier {
     )
 }
 
+/**
+ * Whether a black shadow of [shadowAlpha] is representable over this color, i.e. whether it spans
+ * at least [MIN_SHADOW_QUANTIZATION_STEPS] steps of the 8-bit channel range.
+ */
+private fun Color.canRenderShadow(shadowAlpha: Float): Boolean =
+    maxOf(red, green, blue) * shadowAlpha * MAX_CHANNEL_VALUE >= MIN_SHADOW_QUANTIZATION_STEPS
+
+private const val MATERIAL_SHADOW_ALPHA = 0.12f
+private const val MIN_SHADOW_QUANTIZATION_STEPS = 3f
+private const val MAX_CHANNEL_VALUE = 255f
+
 /** Diagonal gradient stroke that wraps the material variant. */
 @Composable
 private fun Modifier.materialBorder(shape: Shape): Modifier = border(
diff --git a/core/ui/src/main/java/com/tangem/core/ui/extensions/Shadow.kt b/core/ui/src/main/java/com/tangem/core/ui/extensions/Shadow.kt
index bc1ce31389..a5f8b41021 100644
--- a/core/ui/src/main/java/com/tangem/core/ui/extensions/Shadow.kt
+++ b/core/ui/src/main/java/com/tangem/core/ui/extensions/Shadow.kt
@@ -8,9 +8,21 @@ import androidx.compose.ui.graphics.drawscope.clipPath
 import androidx.compose.ui.graphics.drawscope.drawIntoCanvas
 import androidx.compose.ui.unit.Dp
 import androidx.compose.ui.unit.DpOffset
-import androidx.compose.ui.unit.LayoutDirection
 import androidx.compose.ui.unit.dp
 
+/**
+ * Draws a soft drop shadow behind the content.
+ *
+ * @param radius Blur size as authored in the design tool — a Figma / CSS `box-shadow` blur, i.e.
+ *   twice the Gaussian sigma. It is converted to the framework's blur radius internally. Values
+ *   too small to produce a visible blur render nothing.
+ * @param color Shadow color. Only its alpha and hue matter; the shape itself is never filled.
+ * @param shape Shape the shadow is cast from.
+ * @param spread Grows (positive) or shrinks (negative) the shadow relative to [shape].
+ * @param offset Shadow displacement.
+ * @param isAlphaContentClip Cuts [shape]'s own area out of the shadow. Enable it when the content
+ *   drawn on top is translucent, otherwise the blur shows through it.
+ */
 fun Modifier.softLayerShadow(
     radius: Dp = 8.dp,
     color: Color = Color.Black.copy(alpha = .23f),
@@ -19,10 +31,11 @@ fun Modifier.softLayerShadow(
     offset: DpOffset = DpOffset(x = 0.dp, y = 2.dp),
     isAlphaContentClip: Boolean = false,
 ): Modifier = this.drawWithCache {
-    val radiusPx = radius.toPx()
-    require(radiusPx > 0.0F)
+    val radiusPx = designBlurToShadowRadiusPx(radius.toPx())
+    if (radiusPx <= 0f) return@drawWithCache onDrawBehind {}
+
     val paint = Paint().apply {
-        this.color = color
+        this.color = color.copy(alpha = 0f)
 
         asFrameworkPaint().apply {
             isDither = true
@@ -38,7 +51,7 @@ fun Modifier.softLayerShadow(
     }
     val shapeOutline = shape.createOutline(
         size = size,
-        layoutDirection = LayoutDirection.Rtl,
+        layoutDirection = layoutDirection,
         density = this,
     )
     val shapePath = Path().apply {
@@ -86,6 +99,18 @@ fun Modifier.softLayerShadow(
 @Suppress("UnnecessaryParentheses")
 private fun spreadScale(spread: Float, size: Float): Float = 1.0F + ((spread / size) * 2.0F)
 
+/**
+ * Converts a design-tool blur value to the blur radius expected by `Paint.setShadowLayer`.
+ *
+ * A Figma / CSS `box-shadow` blur of `B` describes a Gaussian with `sigma = B / 2`, whereas the
+ * framework derives `sigma = 0.57735 * radius + 0.5`. Passing `B` straight through renders the
+ * shadow ~16% wider than designed.
+ */
+private fun designBlurToShadowRadiusPx(blurPx: Float): Float = (blurPx / 2f - BLUR_SIGMA_INTERCEPT) / BLUR_SIGMA_SLOPE
+
+private const val BLUR_SIGMA_SLOPE = 0.57735f
+private const val BLUR_SIGMA_INTERCEPT = 0.5f
+
 private fun DrawScope.clipShadowByPath(path: Path, block: DrawScope.() -> Unit) {
     clipPath(
         path = path,