Created
June 26, 2022 01:26
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Modifier to highlight recompositions happening on a Composable. Full credit to Google for creating this Modifier. Original link - https://github.com/android/snippets/blob/master/compose/recomposehighlighter/src/main/java/com/example/android/compose/recomposehighlighter/RecomposeHighlighter.kt
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/* | |
* Copyright 2022 Google Inc. | |
* | |
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file | |
* except in compliance with the License. You may obtain a copy of the License at | |
* | |
* http://www.apache.org/licenses/LICENSE-2.0 | |
* | |
* Unless required by applicable law or agreed to in writing, software distributed under the | |
* License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY | |
* KIND, either express or implied. See the License for the specific language governing | |
* permissions and limitations under the License. | |
*/ | |
package com.example.android.compose.recomposehighlighter | |
import androidx.compose.runtime.LaunchedEffect | |
import androidx.compose.runtime.Stable | |
import androidx.compose.runtime.mutableStateOf | |
import androidx.compose.runtime.remember | |
import androidx.compose.ui.Modifier | |
import androidx.compose.ui.composed | |
import androidx.compose.ui.draw.drawWithCache | |
import androidx.compose.ui.geometry.Offset | |
import androidx.compose.ui.geometry.Size | |
import androidx.compose.ui.graphics.Color | |
import androidx.compose.ui.graphics.SolidColor | |
import androidx.compose.ui.graphics.drawscope.Fill | |
import androidx.compose.ui.graphics.drawscope.Stroke | |
import androidx.compose.ui.graphics.lerp | |
import androidx.compose.ui.platform.debugInspectorInfo | |
import androidx.compose.ui.unit.dp | |
import androidx.compose.ui.util.lerp | |
import kotlin.math.min | |
import kotlinx.coroutines.delay | |
/** | |
* A [Modifier] that draws a border around elements that are recomposing. The border increases in | |
* size and interpolates from red to green as more recompositions occur before a timeout. | |
*/ | |
@Stable | |
fun Modifier.recomposeHighlighter(): Modifier = this.then(recomposeModifier) | |
// Use a single instance + @Stable to ensure that recompositions can enable skipping optimizations | |
// Modifier.composed will still remember unique data per call site. | |
private val recomposeModifier = | |
Modifier.composed(inspectorInfo = debugInspectorInfo { name = "recomposeHighlighter" }) { | |
// The total number of compositions that have occurred. We're not using a State<> here be | |
// able to read/write the value without invalidating (which would cause infinite | |
// recomposition). | |
val totalCompositions = remember { arrayOf(0L) } | |
totalCompositions[0]++ | |
// The value of totalCompositions at the last timeout. | |
val totalCompositionsAtLastTimeout = remember { mutableStateOf(0L) } | |
// Start the timeout, and reset everytime there's a recomposition. (Using totalCompositions | |
// as the key is really just to cause the timer to restart every composition). | |
LaunchedEffect(totalCompositions[0]) { | |
delay(3000) | |
totalCompositionsAtLastTimeout.value = totalCompositions[0] | |
} | |
Modifier.drawWithCache { | |
onDrawWithContent { | |
// Draw actual content. | |
drawContent() | |
// Below is to draw the highlight, if necessary. A lot of the logic is copied from | |
// Modifier.border | |
val numCompositionsSinceTimeout = | |
totalCompositions[0] - totalCompositionsAtLastTimeout.value | |
val hasValidBorderParams = size.minDimension > 0f | |
if (!hasValidBorderParams || numCompositionsSinceTimeout <= 0) { | |
return@onDrawWithContent | |
} | |
val (color, strokeWidthPx) = | |
when (numCompositionsSinceTimeout) { | |
// We need at least one composition to draw, so draw the smallest border | |
// color in blue. | |
1L -> Color.Blue to 1f | |
// 2 compositions is _probably_ okay. | |
2L -> Color.Green to 2.dp.toPx() | |
// 3 or more compositions before timeout may indicate an issue. lerp the | |
// color from yellow to red, and continually increase the border size. | |
else -> { | |
lerp( | |
Color.Yellow.copy(alpha = 0.8f), | |
Color.Red.copy(alpha = 0.5f), | |
min(1f, (numCompositionsSinceTimeout - 1).toFloat() / 100f) | |
) to numCompositionsSinceTimeout.toInt().dp.toPx() | |
} | |
} | |
val halfStroke = strokeWidthPx / 2 | |
val topLeft = Offset(halfStroke, halfStroke) | |
val borderSize = Size(size.width - strokeWidthPx, size.height - strokeWidthPx) | |
val fillArea = (strokeWidthPx * 2) > size.minDimension | |
val rectTopLeft = if (fillArea) Offset.Zero else topLeft | |
val size = if (fillArea) size else borderSize | |
val style = if (fillArea) Fill else Stroke(strokeWidthPx) | |
drawRect( | |
brush = SolidColor(color), | |
topLeft = rectTopLeft, | |
size = size, | |
style = style | |
) | |
} | |
} | |
} |
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