Drawing Phase Optimization: Enhance Jetpack Compose Performance

Jetpack Compose offers a declarative way to build UI in Android, simplifying the development process and enhancing code maintainability. However, to achieve optimal performance, it’s crucial to understand and optimize the different phases of the composition process, particularly the drawing phase. This article delves into the drawing phase of Jetpack Compose and provides practical tips to improve your app’s performance.

Understanding the Drawing Phase in Jetpack Compose

The rendering process in Jetpack Compose can be broken down into three primary phases: Composition, Layout, and Drawing. Each phase plays a critical role in transforming your composable functions into visible UI on the screen. Here’s a brief overview:

• Composition: Jetpack Compose runs your composable functions and creates a description of your UI.
• Layout: The framework determines the size and position of each UI element in the layout tree.
• Drawing: Finally, the framework draws the UI elements on the screen based on the layout calculations.

The drawing phase involves rasterizing the UI elements onto a Canvas. Optimizing this phase can significantly reduce the time taken to render the UI, leading to smoother animations, better scrolling performance, and an overall improved user experience.

Why is Drawing Phase Optimization Important?

The drawing phase is often the most expensive part of rendering a UI because it involves pixel-level operations. Poorly optimized drawing can lead to:

• Jank: Jerky or stuttering animations and transitions.
• Slow Rendering: UI elements taking longer to appear, leading to a sluggish feel.
• Increased Battery Consumption: Higher CPU and GPU usage.

Strategies for Drawing Phase Optimization

1. Reducing Overdraw

Overdraw occurs when the system draws a pixel multiple times in the same frame. This often happens when UI elements overlap. Reducing overdraw is one of the most effective ways to optimize the drawing phase.

Techniques to Reduce Overdraw:

• Remove Unnecessary Backgrounds: Avoid setting opaque backgrounds on views that are already covered by other views.
• Clip Drawing: Use the clip modifier to prevent drawing outside the bounds of a composable.
• Use Transparency Wisely: Transparency can cause overdraw if the transparent view is drawn over an opaque one.

Example: Removing Unnecessary Backgrounds

Consider the following example with unnecessary background:

import androidx.compose.foundation.background
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.padding
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp

@Composable
fun OverdrawExample() {
    Box(
        modifier = Modifier
            .fillMaxSize()
            .background(Color.White) // Background 1
    ) {
        Column(
            modifier = Modifier
                .padding(16.dp)
                .background(Color.LightGray) // Background 2 - Unnecessary
        ) {
            Text("Hello, Compose!", modifier = Modifier.padding(8.dp))
            Text("Optimizing Drawing Phase", modifier = Modifier.padding(8.dp))
        }
    }
}

@Preview(showBackground = true)
@Composable
fun OverdrawExamplePreview() {
    OverdrawExample()
}

In the above example, the Column has a background color (Color.LightGray) that covers the Box‘s background (Color.White). This leads to overdraw. To fix this, remove the unnecessary background from the Column:

import androidx.compose.foundation.background
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.padding
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp

@Composable
fun OptimizedOverdrawExample() {
    Box(
        modifier = Modifier
            .fillMaxSize()
            .background(Color.White) // Background 1
    ) {
        Column(
            modifier = Modifier.padding(16.dp) // Removed background
        ) {
            Text("Hello, Compose!", modifier = Modifier.padding(8.dp))
            Text("Optimizing Drawing Phase", modifier = Modifier.padding(8.dp))
        }
    }
}

@Preview(showBackground = true)
@Composable
fun OptimizedOverdrawExamplePreview() {
    OptimizedOverdrawExample()
}

By removing the redundant background, you reduce the number of times the pixels are drawn, improving rendering performance.

2. Using ContentDrawScope

When creating custom drawing operations, ContentDrawScope gives you fine-grained control over what is drawn and how it’s drawn. By understanding the tools provided by ContentDrawScope, you can optimize the drawing operations effectively.

Example: Drawing a Custom Border

Drawing a border with rounded corners efficiently:

import androidx.compose.foundation.border
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.drawBehind
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.graphics.PathEffect
import androidx.compose.ui.graphics.drawscope.Stroke
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp

@Composable
fun CustomBorderExample() {
    Box(
        modifier = Modifier
            .padding(16.dp)
            .drawBehind {
                drawRoundRect(
                    color = Color.Blue,
                    style = Stroke(width = 4.dp.toPx(), pathEffect = PathEffect.cornerPathEffect(8.dp.toPx()))
                )
            }
    ) {
        Text(text = "Custom Border", modifier = Modifier.padding(16.dp))
    }
}

@Preview(showBackground = true)
@Composable
fun CustomBorderExamplePreview() {
    CustomBorderExample()
}

In this example, the drawRoundRect function from ContentDrawScope is used to draw a rounded rectangle border. By using specific drawing functions and controlling the drawing style, you can achieve efficient and customized drawing.

3. Utilizing Hardware Layers

Hardware layers allow you to render a composable into a separate buffer, which can then be composited into the scene. This can be particularly useful for composables that are expensive to render or that are frequently animated.

When to Use Hardware Layers:

• Complex Drawing Operations: If a composable performs complex drawing operations, rendering it into a hardware layer can improve performance.
• Frequent Animations: If a composable is frequently animated, using a hardware layer can reduce the amount of work the system needs to do on each frame.

Example: Using Hardware Layers for Animation

Animating a complex composable:

import androidx.compose.animation.core.animateFloatAsState
import androidx.compose.animation.core.tween
import androidx.compose.foundation.background
import androidx.compose.foundation.clickable
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.size
import androidx.compose.foundation.shape.CircleShape
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.setValue
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.alpha
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.graphics.graphicsLayer
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp

@Composable
fun HardwareLayerAnimationExample() {
    var isClicked by remember { mutableStateOf(false) }
    val alpha: Float by animateFloatAsState(
        targetValue = if (isClicked) 0.5f else 1f,
        animationSpec = tween(durationMillis = 500),
        label = "alphaAnimation"
    )

    Box(
        modifier = Modifier
            .size(100.dp)
            .graphicsLayer(compositingStrategy = androidx.compose.ui.graphics.CompositingStrategy.Offscreen) // Enable hardware layer
            .alpha(alpha)
            .background(Color.Red, shape = CircleShape)
            .clickable { isClicked = !isClicked },
        contentAlignment = Alignment.Center
    ) {
        Text(text = "Tap", color = Color.White)
    }
}

@Preview(showBackground = true)
@Composable
fun HardwareLayerAnimationExamplePreview() {
    HardwareLayerAnimationExample()
}

In this example, graphicsLayer(compositingStrategy = androidx.compose.ui.graphics.CompositingStrategy.Offscreen) enables rendering the Box into a hardware layer. This improves animation performance, especially for more complex composables.

4. Reducing Complexity

The more complex your composable, the more work the system has to do to draw it. Simplifying your composables can improve drawing performance.

Techniques to Reduce Complexity:

• Decompose Large Composables: Break large composables into smaller, more manageable pieces.
• Simplify Custom Drawing: Avoid complex calculations and drawing operations in your custom drawing code.

Example: Decomposing Large Composables

Refactoring a complex UI:

import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.Row
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.tooling.preview.Preview

// Before: Complex Composable
@Composable
fun ComplexUI() {
    Column {
        Row {
            Text("Title 1")
            Text("Value 1")
        }
        Row {
            Text("Title 2")
            Text("Value 2")
        }
    }
}

// After: Decomposed Composables
@Composable
fun DataRow(title: String, value: String) {
    Row {
        Text(title)
        Text(value)
    }
}

@Composable
fun DecomposedUI() {
    Column {
        DataRow("Title 1", "Value 1")
        DataRow("Title 2", "Value 2")
    }
}

@Preview(showBackground = true)
@Composable
fun ComplexUIPreview() {
    ComplexUI()
}

@Preview(showBackground = true)
@Composable
fun DecomposedUIPreview() {
    DecomposedUI()
}

By decomposing the large composable into smaller, reusable components (like DataRow), you can improve code organization and potentially reduce the amount of work needed during the drawing phase.

Tools for Analyzing Drawing Performance

Android Studio provides tools for analyzing drawing performance and identifying potential bottlenecks.

• Profile GPU Rendering: This tool provides a visual representation of the time it takes to render each frame, helping you identify slow frames.
• Layout Inspector: This tool allows you to inspect the layout tree and identify potential issues, such as overdraw.

Conclusion

Optimizing the drawing phase in Jetpack Compose is essential for creating smooth, responsive, and energy-efficient Android applications. By reducing overdraw, utilizing hardware layers, simplifying composables, and using the appropriate drawing APIs, you can significantly improve your app’s performance. Regularly analyzing your app’s rendering performance with Android Studio’s profiling tools will help you identify and address potential bottlenecks, leading to a better user experience.