Add background modifier, fix multimodifier positioning (#180)

mosaic-runtime/src/commonMain/kotlin/com/jakewharton/mosaic/canvas.kt

@@ -96,4 +96,20 @@ internal class TextPixel(var value: String) {
 	var style = None
 
 	constructor(char: Char) : this(char.toString())
+
+	override fun toString() = buildString {
+		append("TextPixel(\"")
+		append(value)
+		append("\"")
+		if (background != null) {
+			append(" bg=")
+			append(background)
+		}
+		if (foreground != null) {
+			append(" fg=")
+			append(foreground)
+		}
+		// TODO style
+		append(')')
+	}
 }

mosaic-runtime/src/commonMain/kotlin/com/jakewharton/mosaic/layout/Background.kt

@@ -0,0 +1,25 @@
+package com.jakewharton.mosaic.layout
+
+import androidx.compose.runtime.Stable
+import com.jakewharton.mosaic.modifier.Modifier
+import com.jakewharton.mosaic.ui.Color
+
+@Stable
+public fun Modifier.background(
+	color: Color,
+): Modifier = this.then(
+	BackgroundModifier(
+		color = color,
+	)
+)
+
+private class BackgroundModifier(
+	private val color: Color,
+) : DrawModifier {
+	override fun ContentDrawScope.draw() {
+		drawRect(color)
+		drawContent()
+	}
+
+	override fun toString() = "Background($color)"
+}

mosaic-runtime/src/commonMain/kotlin/com/jakewharton/mosaic/layout/DrawModifier.kt

@@ -20,6 +20,8 @@ import com.jakewharton.mosaic.modifier.Modifier
 
 public interface DrawModifier : Modifier.Element {
 	public fun ContentDrawScope.draw()
+	// Force subclasses to add a debugging implementation.
+	override fun toString(): String
 }
 
 public fun Modifier.drawBehind(

mosaic-runtime/src/commonMain/kotlin/com/jakewharton/mosaic/layout/DrawScope.kt

@@ -21,7 +21,18 @@ import com.jakewharton.mosaic.ui.Color
 import com.jakewharton.mosaic.ui.TextStyle
 
 public interface DrawScope {
-	public fun write(
+	public val width: Int
+	public val height: Int
+
+	public fun drawRect(
+		color: Color,
+		row: Int = 0,
+		column: Int = 0,
+		width: Int = this.width,
+		height: Int = this.height,
+	)
+
+	public fun drawText(
 		row: Int,
 		column: Int,
 		string: String,
@@ -33,8 +44,24 @@ public interface DrawScope {
 
 internal open class TextCanvasDrawScope(
 	private val canvas: TextCanvas,
+	override val width: Int,
+	override val height: Int,
 ): DrawScope {
-	override fun write(
+	override fun drawRect(
+		color: Color,
+		row: Int,
+		column: Int,
+		width: Int,
+		height: Int,
+	) {
+		for (y in row until row + height) {
+			for (x in column until column + width) {
+				canvas[y, x].background = color
+			}
+		}
+	}
+
+	override fun drawText(
 		row: Int,
 		column: Int,
 		string: String,

mosaic-runtime/src/commonMain/kotlin/com/jakewharton/mosaic/layout/LayoutModifier.kt

@@ -46,6 +46,9 @@ public interface LayoutModifier : Modifier.Element {
 	public fun MeasureScope.measure(
 		measurable: Measurable,
 	): MeasureResult
+
+	// Force subclasses to add a debugging implementation.
+	override fun toString(): String
 }
 
 /**

mosaic-runtime/src/commonMain/kotlin/com/jakewharton/mosaic/layout/Node.kt

@@ -70,54 +70,18 @@ internal class MosaicNode(
 	var debugPolicy: DebugPolicy,
 	val onStaticDraw: (() -> Unit)?,
 ) : Measurable {
-	private val isStatic = onStaticDraw != null
+	val isStatic get() = onStaticDraw != null
 	val children = mutableListOf<MosaicNode>()
 
-	private val bottomLayer: MosaicNodeLayer = object : AbstractMosaicNodeLayer(null, isStatic) {
-		override fun doMeasure(): MeasureResult {
-			return measurePolicy.run { measure(children) }
-		}
-
-		override fun drawTo(canvas: TextCanvas) {
-			for (child in children) {
-				if (child.width != 0 && child.height != 0) {
-					child.topLayer.drawTo(canvas)
-				}
-			}
-		}
-	}
-
-	private var topLayer = bottomLayer
+	private val bottomLayer: MosaicNodeLayer = BottomLayer(this)
+	var topLayer: MosaicNodeLayer = bottomLayer
 
 	var modifiers: Modifier = Modifier
 		set(value) {
 			topLayer = value.foldOut(bottomLayer) { element, lowerLayer ->
 				when (element) {
-					is LayoutModifier -> {
-						object : AbstractMosaicNodeLayer(lowerLayer, false) {
-							override fun doMeasure(): MeasureResult {
-								return element.run { measure(lowerLayer) }
-							}
-						}
-					}
-
-					is DrawModifier -> {
-						object : AbstractMosaicNodeLayer(lowerLayer, false) {
-							override fun drawTo(canvas: TextCanvas) {
-								canvas.translationX += x
-								canvas.translationY += y
-								val scope = object : TextCanvasDrawScope(canvas), ContentDrawScope {
-									override fun drawContent() {
-										lowerLayer.drawTo(canvas)
-									}
-								}
-								element.run { scope.draw() }
-								canvas.translationX -= x
-								canvas.translationY -= y
-							}
-						}
-					}
-
+					is LayoutModifier -> LayoutLayer(element, lowerLayer)
+					is DrawModifier -> DrawLayer(element, lowerLayer)
 					else -> lowerLayer
 				}
 			}
@@ -162,3 +126,48 @@ internal class MosaicNode(
 
 	override fun toString() = debugPolicy.run { renderDebug() }
 }
+
+private class BottomLayer(
+	private val node: MosaicNode,
+) : AbstractMosaicNodeLayer(null, node.isStatic) {
+	override fun doMeasure(): MeasureResult {
+		return node.measurePolicy.run { measure(node.children) }
+	}
+
+	override fun drawTo(canvas: TextCanvas) {
+		for (child in node.children) {
+			if (child.width != 0 && child.height != 0) {
+				child.topLayer.drawTo(canvas)
+			}
+		}
+	}
+}
+
+private class LayoutLayer(
+	private val element: LayoutModifier,
+	private val lowerLayer: MosaicNodeLayer,
+) : AbstractMosaicNodeLayer(lowerLayer, false) {
+	override fun doMeasure(): MeasureResult {
+		return element.run { measure(lowerLayer) }
+	}
+}
+
+private class DrawLayer(
+	private val element: DrawModifier,
+	private val lowerLayer: MosaicNodeLayer,
+) : AbstractMosaicNodeLayer(lowerLayer, false) {
+	override fun drawTo(canvas: TextCanvas) {
+		val oldX = canvas.translationX
+		val oldY = canvas.translationY
+		canvas.translationX = x
+		canvas.translationY = y
+		val scope = object : TextCanvasDrawScope(canvas, width, height), ContentDrawScope {
+			override fun drawContent() {
+				lowerLayer.drawTo(canvas)
+			}
+		}
+		element.run { scope.draw() }
+		canvas.translationX = oldX
+		canvas.translationY = oldY
+	}
+}

mosaic-runtime/src/commonMain/kotlin/com/jakewharton/mosaic/ui/Color.kt

@@ -8,6 +8,8 @@ public class Color private constructor(
 	internal val fg: Int,
 	internal val bg: Int,
 ) {
+	override fun toString(): String = "Color($fg)"
+
 	public companion object {
 		@Stable
 		public val Black: Color = Color(30, 40)

mosaic-runtime/src/commonMain/kotlin/com/jakewharton/mosaic/ui/Text.kt

@@ -12,6 +12,7 @@ import kotlin.jvm.JvmName
 @Composable
 public fun Text(
 	value: String,
+	modifier: Modifier = Modifier,
 	color: Color? = null,
 	background: Color? = null,
 	style: TextStyle? = null,
@@ -27,9 +28,9 @@ public fun Text(
 			layout.measure()
 			layout(layout.width, layout.height)
 		},
-		modifiers = Modifier.drawBehind {
+		modifiers = modifier.drawBehind {
 			layout.lines.forEachIndexed { row, line ->
-				write(row, 0, line, color, background, style)
+				drawText(row, 0, line, color, background, style)
 			}
 		},
 	)

mosaic-runtime/src/commonTest/kotlin/com/jakewharton/mosaic/LayoutTest.kt

@@ -103,7 +103,7 @@ class LayoutTest {
 					Text("..")
 					Layout(modifiers = Modifier.drawBehind {
 						repeat(4) { row ->
-							write(row, 0, "XXXX")
+							drawText(row, 0, "XXXX")
 						}
 					}) {
 						layout(2, 2)

samples/jest/src/main/kotlin/example/jest.kt

@@ -10,6 +10,9 @@ import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.runtime.snapshots.Snapshot
 import androidx.compose.runtime.snapshots.SnapshotStateList
+import com.jakewharton.mosaic.layout.background
+import com.jakewharton.mosaic.layout.padding
+import com.jakewharton.mosaic.modifier.Modifier
 import com.jakewharton.mosaic.runMosaicBlocking
 import com.jakewharton.mosaic.ui.Color.Companion.Black
 import com.jakewharton.mosaic.ui.Color.Companion.BrightBlack
@@ -96,13 +99,18 @@ fun TestRow(test: Test) {
 			Pass -> Green
 			Fail -> Red
 		}
-		// TODO use start/end padding of 1 to achieve spacing
 		val state = when (test.state) {
-			Running -> " RUNS "
-			Pass -> " PASS "
-			Fail -> " FAIL "
+			Running -> "RUNS"
+			Pass -> "PASS"
+			Fail -> "FAIL"
 		}
-		Text(state, color = Black, background = bg)
+		Text(
+			state,
+			modifier = Modifier
+				.background(bg)
+				.padding(horizontal = 1),
+			color = Black
+		)
 
 		val dir = test.path.substringBeforeLast('/')
 		val name = test.path.substringAfterLast('/')