Android UI Performance: GPU Overdraw

Introduction

Ensuring optimal performance in Android applications is crucial for providing a smooth user experience and preserving device battery life. In this post, we will go into two significant aspects of UI performance: overdraw and rendering. We'll explore what they are, how to debug and analyze them, and provide real-life examples and strategies for improvement. We'll also cover how to use the Android Studio Profiler to diagnose and optimize performance issues related to CPU, memory, and energy usage.

UI Performance Overdraw

What is an overdraw?

Overdraw occurs when your app draws the same pixel more than once within the same frame. This is a common performance issue because, in most cases, pixels that are overdrawn do not end up contributing to the final rendered image.

Why is Visualizing GPU Overdraw Important?

Visualizing GPU overdraw is crucial for several reasons:

**Performance Optimization: **By identifying areas with excessive overdraw, developers can pinpoint inefficiencies. High overdraw can lead to increased battery consumption and reduced performance, causing apps to run slower and devices to overheat.

**Rendering Efficiency: **Visualizing overdraw helps developers understand where they can minimize unnecessary rendering. This leads to smoother animations and faster load times, enhancing the overall user experience.

Resource Management: Understanding and managing overdraw ensures better utilization of GPU resources, allowing more complex and visually appealing applications without compromising performance.

By employing visualization tools that color-code elements based on their rendering frequency, developers can easily spot problem areas and optimize their applications. This proactive approach is key to maintaining robust and efficient mobile applications in a competitive app market.

In other terms, an application might be doing more rendering work than necessary, which can be a performance problem due to the extra GPU effort to render pixels that won’t be visible to the user.

Analyzing an overdraw

Once you enable this flag, Android shows overdraw amounts on your screen by tinting pixels in different colors. If you’ve only rendered a pixel one time, you should see it in its true color with no tint.

However, as the overdraw increases, so do the colors. 1x overdraw, for example, is tinted blue, meaning that you’ve now redrawn this pixel one extra time. 2x, 3x, and 4x overdraw follow the same pattern.

Interpreting the Debug GPU Overdraw Output: A Color Guide The color key for Debug GPU Overdraw output is essential for understanding the level of overdraw affecting each pixel on your screen. Here's a breakdown of what each color signifies in this context:

True Color: This indicates that no overdraw is occurring, ensuring optimal performance as each pixel is drawn only once.

Blue: A blue hue signifies that a pixel is drawn twice, introducing some overdraw that could impact performance slightly.

**Green: **When you see green, it means the pixel is overdrawn three times, suggesting moderate performance concerns that may need attention.

**Pink: **A pink color indicates that the pixel is drawn four times, which could significantly affect performance and warrants investigation for optimization.

Red: Red signifies a severe level of overdraw, with pixels being drawn five or more times. This level of overdraw can severely impact performance, necessitating immediate corrective action.

Real-life examples

Now that we know what GPU Overdraw means, let’s take a look at some popular apps and see how they perform.

As you can see from these screenshots, very few apps take into consideration overdraw optimization. While it doesn’t directly affect the application’s performance, it does increase battery usage due to additional GPU rendering effort.

Fixing an overdraw

Fixing an overdraw heavily depends on the complexity of the application’s screens. However, several strategies can help reduce or eliminate overdraw. Let's look at the most common fix: removing unneeded backgrounds in layouts.

Removing unneeded backgrounds in layouts

Here's an example of views being overdrawn. All the red areas in the image suggest that the views are redrawn on top of each other. Let's look at the code and figure out what's wrong.

Here we have a parent RelativeLayout with a white background, a child LinearLayout also with a white background, and another child TextView with a white background.

Now it is very important that you notice that the white color is being used multiple times in the code. First the RelativeLayout is drawn with the white background, then the child LinearLayout also draws a white color, and the TextView draws white again.

Therefore, we are wasting GPU cycles here by redrawing on the same pixels multiple times. Note that this is not because the colors are same, but because we are redrawing the pixels again and again.

We now know that the color white is being drawn multiple times on the same view. All we have to do is to remove the white background from the LinearLayout and the TextView.

After changes in the code the overdraw is much lesser, we can now see that there are no more red marks, meaning that there is no heavy overdraw happening anymore.

Other practices

There are many other common practices that one can follow to reduce overdraw, some of them are:

• Removing invisible views. That is, removing views that are completely covered by other views.
• Reducing the use of transparency. For example, instead of using transparency to create a color, just find that color. Instead of using transparency to create a shine-through effect for two overlapping images, preprocess the two images into one.
• Flattening and reorganizing the view hierarchy to reduce the number of views.
• Resizing or rearranging the views so that they do not overlap.

Understanding GPU Overdraw: Benefits in App Development

Enhance Performance Recognizing GPU overdraw is crucial for optimizing an app’s performance. By pinpointing areas where rendering is excessive, developers can streamline processes, reducing the workload on the device’s graphics processor. This leads to smoother animations and a more responsive user interface, providing a better experience for users across various devices.

Improve Battery Life

Excessive rendering not only slows down performance but also drains the battery faster. By minimizing overdraw, developers can ensure their app is more energy-efficient. This optimization helps extend battery life, which is a significant concern for users, especially those who frequently use resource-intensive applications.

Reduce Excess Resource Usage

An app that efficiently manages GPU overdraw avoids unnecessary use of computational power and system resources. This not only improves the app’s overall footprint but also allows it to run more efficiently alongside other applications. The reduction in resource consumption can be critical in environments where device capabilities are limited, ensuring broader compatibility and performance consistency.

Enhance User Experience

Ultimately, understanding and addressing GPU overdraw contributes to a seamless user experience. By reducing lag and preventing visual stutters, apps can deliver a polished, professional look and feel. Users are more likely to engage with and recommend applications that run smoothly and look appealing, driving greater satisfaction and retention.

Streamline Development and Debugging

Early identification of overdraw issues can simplify the development and debugging process. Developers can more easily focus their efforts on optimizing problematic areas, speeding up development cycles. This proactive approach can prevent potential performance issues from arising post-launch, saving time and effort in the long run.

In summary, understanding GPU overdraw is essential for app developers aiming to boost performance, improve battery efficiency, and enhance the overall user experience.