nice border around images in the dark theme

composeApp/src/commonMain/kotlin/net/sergeych/toread/ReaderContent.kt

@@ -43,8 +43,13 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
 import androidx.compose.ui.draw.drawWithContent
 import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.geometry.Size
+import androidx.compose.ui.graphics.BlendMode
+import androidx.compose.ui.graphics.Brush
 import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.CompositingStrategy
 import androidx.compose.ui.graphics.StrokeCap
+import androidx.compose.ui.graphics.graphicsLayer
 import androidx.compose.ui.input.pointer.PointerEventPass
 import androidx.compose.ui.input.pointer.PointerType
 import androidx.compose.ui.input.pointer.pointerInput
@@ -81,6 +86,7 @@ import net.sergeych.toread.fb2.Fb2TextSpan
 import net.sergeych.toread.fb2.Fb2TextStyle
 import net.sergeych.toread.text.HyphenationRegistry
 import net.sergeych.toread.text.SoftHyphen
+import kotlin.math.min
 import kotlinx.coroutines.launch
 import kotlin.math.max
 import kotlin.math.min
@@ -579,6 +585,8 @@ private fun BookImage(
     }
     val imageTitle = image?.alt?.ifBlank { null } ?: book.title
     val imageBackgroundColor = readerImageBackgroundColor()
+    val imageShape = RoundedCornerShape(8.dp)
+    val smoothImageEdges = imageBackgroundColor != MaterialTheme.colorScheme.surface
     val density = LocalDensity.current
     BoxWithConstraints(
         modifier = modifier
@@ -612,7 +620,12 @@ private fun BookImage(
             } else {
                 Modifier.fillMaxSize()
             }
-            Box(imageModifier.background(imageBackgroundColor)) {
+            Box(
+                imageModifier
+                    .then(if (smoothImageEdges) Modifier.softImageEdgeFade() else Modifier)
+                    .clip(imageShape)
+                    .background(imageBackgroundColor),
+            ) {
                 Image(
                     bitmap = bitmap,
                     contentDescription = imageTitle,
@@ -626,6 +639,59 @@ private fun BookImage(
     }
 }
 
+private fun Modifier.softImageEdgeFade(): Modifier =
+    graphicsLayer {
+        compositingStrategy = CompositingStrategy.Offscreen
+    }.drawWithContent {
+        drawContent()
+
+        val fade = min(8.dp.toPx(), min(size.width, size.height) / 4f)
+        if (fade <= 0f) return@drawWithContent
+
+        drawRect(
+            brush = Brush.verticalGradient(
+                0f to Color.Transparent,
+                1f to Color.Black,
+                startY = 0f,
+                endY = fade,
+            ),
+            size = Size(size.width, fade),
+            blendMode = BlendMode.DstIn,
+        )
+        drawRect(
+            brush = Brush.verticalGradient(
+                0f to Color.Black,
+                1f to Color.Transparent,
+                startY = size.height - fade,
+                endY = size.height,
+            ),
+            topLeft = Offset(0f, size.height - fade),
+            size = Size(size.width, fade),
+            blendMode = BlendMode.DstIn,
+        )
+        drawRect(
+            brush = Brush.horizontalGradient(
+                0f to Color.Transparent,
+                1f to Color.Black,
+                startX = 0f,
+                endX = fade,
+            ),
+            size = Size(fade, size.height),
+            blendMode = BlendMode.DstIn,
+        )
+        drawRect(
+            brush = Brush.horizontalGradient(
+                0f to Color.Black,
+                1f to Color.Transparent,
+                startX = size.width - fade,
+                endX = size.width,
+            ),
+            topLeft = Offset(size.width - fade, 0f),
+            size = Size(fade, size.height),
+            blendMode = BlendMode.DstIn,
+        )
+    }
+
 private fun Fb2Text.toAnnotatedString(
     language: String?,
     hyphenation: HyphenationRegistry,