feat(placeholder): draw deterministic hand-drawn squiggle

spark-screenshot-testing/src/test/kotlin/com/adevinta/spark/placeholder/PlaceholderDocumentationScreenshots.kt

@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2025 Adevinta
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package com.adevinta.spark.placeholder
+
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Column
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
+import com.adevinta.spark.DefaultTestDevices
+import com.adevinta.spark.components.placeholder.textPlaceholder
+import com.adevinta.spark.components.text.Text
+import com.adevinta.spark.paparazziRule
+import com.adevinta.spark.sparkDocSnapshot
+import com.android.ide.common.rendering.api.SessionParams.RenderingMode.SHRINK
+import org.junit.Rule
+import org.junit.Test
+
+internal class PlaceholderDocumentationScreenshots {
+
+    @get:Rule
+    val paparazzi = paparazziRule(
+        renderingMode = SHRINK,
+        deviceConfig = DefaultTestDevices.DocPhone,
+    )
+
+    @Test
+    fun textPlaceholder() = paparazzi.sparkDocSnapshot {
+        Column(verticalArrangement = Arrangement.spacedBy(8.dp)) {
+            Text(
+                text = "Short",
+                modifier = Modifier.textPlaceholder(visible = true),
+            )
+            Text(
+                text = "A longer placeholder line",
+                modifier = Modifier.textPlaceholder(visible = true),
+            )
+            Text(
+                text = "Another distinct width here",
+                modifier = Modifier.textPlaceholder(visible = true),
+            )
+            Text(
+                text = "A multi-line placeholder that wraps across several lines so each " +
+                    "text line draws its own squiggle instead of one stroke for the whole block",
+                modifier = Modifier.textPlaceholder(visible = true),
+            )
+        }
+    }
+}

spark/src/main/kotlin/com/adevinta/spark/components/placeholder/HandDrawnTextPlaceholder.kt

@@ -0,0 +1,100 @@
+/*
+ * Copyright (c) 2023 Adevinta
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package com.adevinta.spark.components.placeholder
+
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.graphics.Path
+import androidx.compose.ui.graphics.StrokeCap
+import androidx.compose.ui.graphics.StrokeJoin
+import androidx.compose.ui.graphics.drawscope.Stroke
+import kotlin.math.max
+import kotlin.math.roundToInt
+import kotlin.random.Random
+
+private const val STROKE_WIDTH_FRACTION = 0.42f
+private const val AMPLITUDE_FRACTION = 0.14f
+private const val MIN_STROKE_WIDTH_PX = 3f
+
+/**
+ * Builds the squiggle points for each text line, one inner list per line.
+ *
+ * The placeholder box is split into [lineCount] equal horizontal bands, one per text line. Each
+ * band holds one squiggle centred on the band. The seed is derived purely from the integer-pixel
+ * dimensions and the line index, so two placeholders with identical width, height and line count
+ * always produce the same geometry with no per-frame randomness, and each line differs from the
+ * others.
+ *
+ * - The first and last points of a line sit on the band centre line.
+ * - Interior points are displaced vertically by a seeded random fraction of the amplitude.
+ * - Segment count grows with the band aspect ratio, so wider placeholders have more waves.
+ */
+internal fun buildSquigglePoints(widthPx: Float, heightPx: Float, lineCount: Int): List<List<Offset>> {
+    val lines = max(1, lineCount)
+    val band = heightPx / lines
+    val amplitude = band * AMPLITUDE_FRACTION
+    return List(lines) { line ->
+        val seed = widthPx.roundToInt().toLong() * 100_000L + heightPx.roundToInt().toLong() * 31L + line
+        val rng = Random(seed)
+        val centreY = band * (line + 0.5f)
+        val segmentCount = max(2, (widthPx / band).roundToInt())
+        List(segmentCount + 1) { i ->
+            val x = i * widthPx / segmentCount
+            val y = when (i) {
+                0, segmentCount -> centreY
+                else -> centreY + (rng.nextFloat() * 2f - 1f) * amplitude
+            }
+            Offset(x, y)
+        }
+    }
+}
+
+/**
+ * Builds a smooth [Path] through the squiggle points using quadratic Bézier midpoint subdivision.
+ *
+ * The path holds one squiggle sub-path per text line. Each point acts as a Bézier control point;
+ * the midpoint between it and its successor is the on-curve destination. Each line finishes with a
+ * straight segment to its last point, which sits on the band centre line.
+ */
+internal fun buildSquigglePath(widthPx: Float, heightPx: Float, lineCount: Int): Path {
+    val lines = buildSquigglePoints(widthPx, heightPx, lineCount)
+    return Path().apply {
+        for (points in lines) {
+            moveTo(points.first().x, points.first().y)
+            for (i in 0 until points.size - 1) {
+                val midX = (points[i].x + points[i + 1].x) / 2f
+                val midY = (points[i].y + points[i + 1].y) / 2f
+                quadraticTo(points[i].x, points[i].y, midX, midY)
+            }
+            lineTo(points.last().x, points.last().y)
+        }
+    }
+}
+
+/**
+ * Returns a [Stroke] proportional to one text line height, with rounded caps and joins to
+ * reinforce the hand-drawn character of the squiggle.
+ */
+internal fun buildSquiggleStroke(lineHeightPx: Float): Stroke = Stroke(
+    width = max(MIN_STROKE_WIDTH_PX, lineHeightPx * STROKE_WIDTH_FRACTION),
+    cap = StrokeCap.Round,
+    join = StrokeJoin.Round,
+)

spark/src/main/kotlin/com/adevinta/spark/components/placeholder/Placeholder.kt

@@ -30,6 +30,7 @@ import androidx.compose.foundation.layout.size
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Shape
+import androidx.compose.ui.tooling.preview.PreviewFontScale
 import androidx.compose.ui.tooling.preview.PreviewLightDark
 import androidx.compose.ui.unit.dp
 import com.adevinta.spark.PreviewTheme
@@ -59,7 +60,9 @@ public fun Modifier.placeholder(visible: Boolean): Modifier = basePlaceholder(vi
 /**
  * Draws some skeleton UI which is typically used whilst content is 'loading'.
  *
- * The shape is not customizable as it's meant to display the same style for each text placeholders.
+ * The modifier draws a hand-drawn squiggle stroke. The geometry is derived only from the placeholder
+ * size: two placeholders with the same integer pixel width and height draw the same squiggle, and
+ * any size difference draws a different squiggle.
  *
  * A cross-fade transition will be applied to the content and placeholder UI when the [visible]
  * value changes.
@@ -76,7 +79,7 @@ public fun Modifier.placeholder(visible: Boolean): Modifier = basePlaceholder(vi
  */
 public fun Modifier.textPlaceholder(visible: Boolean): Modifier = basePlaceholder(
     visible = visible,
-    useFullShape = true,
+    handDrawnText = true,
 )
 
 /**
@@ -109,6 +112,7 @@ public fun Modifier.illustrationPlaceholder(
 )
 
 @PreviewLightDark
+@PreviewFontScale
 @Composable
 internal fun PreviewPlaceHolder() {
     PreviewTheme {

spark/src/main/kotlin/com/adevinta/spark/components/placeholder/Placeholder.md

@@ -40,8 +40,10 @@ Box(
 
 #### `Modifier.textPlaceholder`
 
-Skeleton for text content. Uses `SparkTheme.shapes.full` (pill shape) to mirror the rounded
-profile of text runs. Animation is a **fade**.
+Skeleton for text content. Draws a hand-drawn squiggle stroke using `SparkTheme` colour tokens.
+The geometry is derived deterministically from the placeholder size: two placeholders with the
+same integer pixel width and height always draw the same stroke, and any size difference draws a
+different stroke. Animation is a **fade**.
 
 ```kotlin
 Text(