Add shadow and config

app/src/main/java/eu/wewox/pagecurl/page/CurlDraw.kt

@@ -1,23 +1,53 @@
 package eu.wewox.pagecurl.page
 
+import android.graphics.Bitmap
+import android.graphics.Canvas
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.draw.drawWithContent
+import androidx.compose.ui.draw.CacheDrawScope
+import androidx.compose.ui.draw.drawWithCache
 import androidx.compose.ui.geometry.Offset
 import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.Paint
 import androidx.compose.ui.graphics.Path
+import androidx.compose.ui.graphics.asAndroidPath
+import androidx.compose.ui.graphics.drawscope.ContentDrawScope
 import androidx.compose.ui.graphics.drawscope.clipPath
+import androidx.compose.ui.graphics.drawscope.drawIntoCanvas
 import androidx.compose.ui.graphics.drawscope.rotateRad
 import androidx.compose.ui.graphics.drawscope.withTransform
+import androidx.compose.ui.graphics.nativeCanvas
+import androidx.compose.ui.graphics.toArgb
+import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.dp
+import eu.wewox.pagecurl.utils.Polygon
+import eu.wewox.pagecurl.utils.lineLineIntersection
 import java.lang.Float.max
 import kotlin.math.atan2
 
+data class CurlConfig(
+    val shadow: ShadowConfig = ShadowConfig()
+) {
+    data class ShadowConfig(
+        val color: Color = Color.Black,
+        val alpha: Float = 0.2f,
+        val radius: Dp = 40.dp,
+        val offsetX: Dp = 0.dp,
+        val offsetY: Dp = 0.dp,
+    )
+}
+
 fun Modifier.drawCurl(
+    config: CurlConfig = CurlConfig(),
     posA: Offset?,
     posB: Offset?,
-): Modifier = drawWithContent {
+): Modifier = drawWithCache {
+    fun drawOnlyContent() =
+        onDrawWithContent {
+            drawContent()
+        }
+
     if (posA == null || posB == null) {
-        drawContent()
-        return@drawWithContent
+        return@drawWithCache drawOnlyContent()
     }
 
     val topIntersection = lineLineIntersection(
@@ -29,51 +59,128 @@ fun Modifier.drawCurl(
         posA, posB
     )
     if (topIntersection == null || bottomIntersection == null) {
-        drawContent()
-        return@drawWithContent
+        return@drawWithCache drawOnlyContent()
     }
 
     val topCurlOffset = Offset(max(0f, topIntersection.x), topIntersection.y)
     val bottomCurlOffset = Offset(max(0f, bottomIntersection.x), bottomIntersection.y)
 
-    val lineVector = topCurlOffset - bottomCurlOffset
+    val clippedContent = prepareClippedContent(topCurlOffset, bottomCurlOffset)
+    val shadowBelowCurl = prepareShadowBelowCurl(config.shadow, topCurlOffset, bottomCurlOffset)
+    val curl = prepareCurl(topCurlOffset, bottomCurlOffset)
 
+    onDrawWithContent {
+        clippedContent()
+        shadowBelowCurl()
+        curl()
+    }
+}
+
+private fun CacheDrawScope.prepareClippedContent(
+    topCurlOffset: Offset,
+    bottomCurlOffset: Offset,
+): ContentDrawScope.() -> Unit {
     val path = Path()
     path.lineTo(topCurlOffset.x, topCurlOffset.y)
     path.lineTo(bottomCurlOffset.x, bottomCurlOffset.y)
     path.lineTo(0f, size.height)
-    clipPath(path) { this@drawWithContent.drawContent() }
-
-    withTransform({
-        scale(-1f, 1f, pivot = bottomCurlOffset)
-
-        val angle = atan2(-lineVector.y, lineVector.x)
-        rotateRad(Math.PI.toFloat() + 2 * angle, pivot = bottomCurlOffset)
-
-        val path2 = Path()
-        path2.moveTo(topCurlOffset.x, topCurlOffset.y)
-        path2.lineTo(max(size.width, topCurlOffset.x), topCurlOffset.y)
-        path2.lineTo(max(size.width, bottomCurlOffset.x), bottomCurlOffset.y)
-        path2.lineTo(bottomCurlOffset.x, bottomCurlOffset.y)
-        clipPath(path2)
-    }) {
-        this@drawWithContent.drawContent()
-        drawRect(Color.White.copy(alpha = 0.8f))
+    return result@{
+        clipPath(path) {
+            this@result.drawContent()
+        }
     }
 }
 
-private fun lineLineIntersection(
-    line1a: Offset,
-    line1b: Offset,
-    line2a: Offset,
-    line2b: Offset,
-): Offset? {
-    val denominator = (line1a.x - line1b.x) * (line2a.y - line2b.y) - (line1a.y - line1b.y) * (line2a.x - line2b.x)
-    if (denominator == 0f) return null
+private fun CacheDrawScope.prepareShadowBelowCurl(
+    shadow: CurlConfig.ShadowConfig,
+    topCurlOffset: Offset,
+    bottomCurlOffset: Offset,
+): ContentDrawScope.() -> Unit {
+    val shadowColor = shadow.color.copy(alpha = shadow.alpha).toArgb()
+    val transparent = shadow.color.copy(alpha = 0f).toArgb()
 
-    val x = ((line1a.x * line1b.y - line1a.y * line1b.x) * (line2a.x - line2b.x) -
-            (line1a.x - line1b.x) * (line2a.x * line2b.y - line2a.y * line2b.x)) / denominator
-    val y = ((line1a.x * line1b.y - line1a.y * line1b.x) * (line2a.y - line2b.y) -
-            (line1a.y - line1b.y) * (line2a.x * line2b.y - line2a.y * line2b.x)) / denominator
-    return Offset(x, y)
+    val paint = Paint()
+    val frameworkPaint = paint.asFrameworkPaint()
+    frameworkPaint.color = transparent
+
+    val radius = shadow.radius.toPx()
+    frameworkPaint.setShadowLayer(
+        shadow.radius.toPx(),
+        shadow.offsetX.toPx(),
+        shadow.offsetY.toPx(),
+        shadowColor
+    )
+
+    val bitmap = Bitmap.createBitmap((size.width + radius * 4).toInt(), (size.height + radius * 4).toInt(), Bitmap.Config.ARGB_8888)
+    bitmap.eraseColor(Color.Transparent.toArgb())
+    val canvas = Canvas(bitmap)
+
+    val path = Polygon(
+        sequence {
+            if (topCurlOffset.x < size.width) {
+                yield(topCurlOffset)
+                yield(Offset(size.width, topCurlOffset.y))
+            } else {
+                val a = lineLineIntersection(topCurlOffset, bottomCurlOffset, Offset(size.width, 0f), Offset(size.width, size.height))!!
+                yield(a)
+                yield(a)
+            }
+            if (bottomCurlOffset.x < size.width) {
+                yield(Offset(size.width, size.height))
+                yield(bottomCurlOffset)
+            } else {
+                val a = lineLineIntersection(topCurlOffset, bottomCurlOffset, Offset(size.width, 0f), Offset(size.width, size.height))!!
+                yield(a)
+                yield(a)
+            }
+        }.toList()
+    ).translate(
+        Offset(2 * radius, 2 * radius)
+    ).offset(
+        radius
+    ).toPath()
+
+    canvas.drawPath(path.asAndroidPath(), frameworkPaint)
+
+    return {
+        val lineVector = topCurlOffset - bottomCurlOffset
+        val angle = atan2(-lineVector.y, lineVector.x)
+
+        withTransform({
+            scale(-1f, 1f, pivot = bottomCurlOffset)
+
+            rotateRad(Math.PI.toFloat() + 2 * angle, pivot = bottomCurlOffset)
+        }) {
+            drawIntoCanvas {
+                it.nativeCanvas.drawBitmap(bitmap, -2 * radius, -2 * radius, null)
+            }
+        }
+    }
+}
+
+private fun CacheDrawScope.prepareCurl(
+    topCurlOffset: Offset,
+    bottomCurlOffset: Offset,
+): ContentDrawScope.() -> Unit {
+    val lineVector = topCurlOffset - bottomCurlOffset
+    val angle = atan2(-lineVector.y, lineVector.x)
+
+    val path = Path()
+    path.moveTo(topCurlOffset.x, topCurlOffset.y)
+    path.lineTo(max(size.width, topCurlOffset.x), topCurlOffset.y)
+    path.lineTo(max(size.width, bottomCurlOffset.x), bottomCurlOffset.y)
+    path.lineTo(bottomCurlOffset.x, bottomCurlOffset.y)
+
+    return result@{
+        withTransform({
+            scale(-1f, 1f, pivot = bottomCurlOffset)
+
+            rotateRad(Math.PI.toFloat() + 2 * angle, pivot = bottomCurlOffset)
+
+            clipPath(path)
+        }) {
+            this@result.drawContent()
+            drawRect(Color.White.copy(alpha = 0.8f))
+        }
+    }
 }

app/src/main/java/eu/wewox/pagecurl/page/Page.kt

@@ -1,5 +1,6 @@
 package eu.wewox.pagecurl.page
 
+import android.view.View
 import androidx.compose.foundation.Image
 import androidx.compose.foundation.background
 import androidx.compose.foundation.layout.Box
@@ -15,9 +16,11 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.geometry.Offset
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.layout.ContentScale
+import androidx.compose.ui.platform.ComposeView
 import androidx.compose.ui.res.painterResource
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
+import androidx.compose.ui.viewinterop.AndroidView
 import eu.wewox.pagecurl.R
 import eu.wewox.pagecurl.utils.Data
 
@@ -35,7 +38,7 @@ fun Page() {
     var posA by remember { mutableStateOf<Offset?>(null) }
     var posB by remember { mutableStateOf<Offset?>(null) }
 
-    Box(
+    SoftwareLayerComposable(
         Modifier
             .curlGesture(
                 onCurl = { a, b ->
@@ -47,22 +50,40 @@ fun Page() {
                     posB = null
                 }
             )
-            .drawCurl(posA, posB)
+            .drawCurl(CurlConfig(), posA, posB)
     ) {
-        //        Text(
-        //            text = Data.Lorem1,
-        //            fontSize = 22.sp,
-        //            modifier = Modifier
-        //                .fillMaxSize()
-        //                .background(Color.White)
-        //                .padding(16.dp)
-        //        )
-        Image(
-            painter = painterResource(R.drawable.img_sleep),
-            contentDescription = null,
-            contentScale = ContentScale.Crop,
-            modifier = Modifier
-                .fillMaxSize()
-        )
+                Text(
+                    text = Data.Lorem1,
+                    fontSize = 22.sp,
+                    modifier = Modifier
+                        .fillMaxSize()
+                        .background(Color.White)
+                        .padding(16.dp)
+                )
+//        Image(
+//            painter = painterResource(R.drawable.img_sleep),
+//            contentDescription = null,
+//            contentScale = ContentScale.Crop,
+//            modifier = Modifier
+//                .fillMaxSize()
+//        )
     }
 }
+
+@Composable
+fun SoftwareLayerComposable(
+    modifier: Modifier = Modifier,
+    content: @Composable () -> Unit,
+) {
+    AndroidView(
+        factory = { context ->
+            ComposeView(context).apply {
+                setLayerType(View.LAYER_TYPE_SOFTWARE, null)
+            }
+        },
+        update = { composeView ->
+            composeView.setContent(content)
+        },
+        modifier = modifier,
+    )
+}

app/src/main/java/eu/wewox/pagecurl/utils/MathUtils.kt

@@ -0,0 +1,63 @@
+package eu.wewox.pagecurl.utils
+
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.graphics.Path
+
+data class Polygon(val vertices: List<Offset>) {
+
+    private val size: Int = vertices.size
+
+    fun translate(offset: Offset): Polygon =
+        Polygon(vertices.map { it + offset })
+
+    fun offset(value: Float): Polygon {
+        val edgeNormals = List(size) {
+            val edge = vertices[index(it + 1)] - vertices[index(it)]
+            Offset(edge.y, -edge.x).normalized()
+        }
+
+        val vertexNormals = List(size) {
+            (edgeNormals[index(it - 1)] + edgeNormals[index(it)]).normalized()
+        }
+
+        return Polygon(
+            vertices.mapIndexed { index, vertex ->
+                vertex + vertexNormals[index] * value
+            }
+        )
+    }
+
+    fun toPath(): Path =
+        Path().apply {
+            vertices.forEachIndexed { index, vertex ->
+                if (index == 0) {
+                    moveTo(vertex.x, vertex.y)
+                } else {
+                    lineTo(vertex.x, vertex.y)
+                }
+            }
+        }
+
+    private fun index(i: Int) = ((i % size) + size) % size
+}
+
+private fun Offset.normalized(): Offset {
+    val distance = getDistance()
+    return if (distance != 0f) this / distance else this
+}
+
+internal fun lineLineIntersection(
+    line1a: Offset,
+    line1b: Offset,
+    line2a: Offset,
+    line2b: Offset,
+): Offset? {
+    val denominator = (line1a.x - line1b.x) * (line2a.y - line2b.y) - (line1a.y - line1b.y) * (line2a.x - line2b.x)
+    if (denominator == 0f) return null
+
+    val x = ((line1a.x * line1b.y - line1a.y * line1b.x) * (line2a.x - line2b.x) -
+            (line1a.x - line1b.x) * (line2a.x * line2b.y - line2a.y * line2b.x)) / denominator
+    val y = ((line1a.x * line1b.y - line1a.y * line1b.x) * (line2a.y - line2b.y) -
+            (line1a.y - line1b.y) * (line2a.x * line2b.y - line2a.y * line2b.x)) / denominator
+    return Offset(x, y)
+}