Level 2 Unity UI Developer: The Guru's UI Development Diagram

Level 2 Unity UI Developer: The Guru's UI Development Diagram

Here we are with a Venn Diagram. I decided to call it The Guru's UI Development Diagram.

There we see three big chunks related to Unity UI Optimization: CPU, GPU, and Developer. Those are the main resources you will have to spare when developing UI.

I want to give you a short overview before we start digging into the topics.

You pay the CPU toll mainly when generating and submitting batches of UI. You can think of them as UI components, such as images. The more of those you have, the more strain you will put in your processor.

The turn for the GPU. You pay the GPU resources mostly in concept of overdraw. This means, stacking layers of graphics on top of each other.

Lastly, the developer's pain is paid in time. You spend time every time you design or maintain your UI. Unity offers you some tools to make it easier for you, e.g. auto-layout helpers.

The cost of the three components rely mostly on you, but they sometimes counteract each other. It's very challenging to perform in every aspect, unless you are very experienced and you have the right tools.

Eventually, you will get there.

I would like you to have a closer look at the attached Guru's UI Development Diagram.

You might be confused. That's alright because we are going to cover each section separately. You will get to understand all of it.

For now, you only have to understand one thing: in the end, it will be up to you to find the balance between the three variables in your game.

Before we start with each component, have a look at these general rules:

• The easier you want the UI design workflow to be, the less performant your UI will be.
• If you want more GPU performance, you will have to focus on finely tweaking graphical elements and avoid element stacking.
• For more CPU performance, you will need to reduce the amount of graphical elements present in the hierarchy.

Let's move on, I can't wait to show you the CPU side of Unity UI Optimization!

Level 2 Unity UI Developer: The CPU

Level 2 Unity UI Developer: The CPU

In my opinion, this is very simple.

The golden rule is:

Every time you add a UI component in your scene, you are adding CPU overhead

Each component increases the CPU cost for the following reasons:

• RectTransform calculation: this is pretty much free in simple canvas hierarchies. However, your CPU will have a harder time if you are using auto-layout components to ease your UI design workflow, such as vertical layout groups and such. The issue with those is that most RectTransforms present in the hierarchy will now depend on each other, so the calculation becomes more complex.
• Vertex generation: the GPU understands vertices, thus those must be provided by the CPU. Vertices must be generated based on the entire canvas hierarchy of the involved RectTransform elements. The vertices depend as well on the specific type of UI element you added (images, texts). Under this category, we also include the cost for the CPU to add other per-vertex attributes such as colors and UVs.

• Dynamic batching: because draw calls are expensive, Unity does its best to dynamically batch as many of them as possible.
  Think of this as combining a large number of small groups of vertices into a single, huge group of vertices. Because... would you rather go to the supermarket ten times to bring an apple each, or go just once and grab them all together?
  Batching is, however, an expensive operation for the CPU which increases with the amount of UI elements you have.
• Draw call emission: finally, the generated batches must be sent to the GPU. These graphical processing units are very picky with the data formats they accept, so the CPU has to make extra work to pack them in a way that they like.

This is expensive, yes. But luckily for us, Unity is kind of smart and caches the canvas so these expensive processes do not happen in every frame.

Just as I brought you good news, I will give you the bad ones: this cache is super easy to break.

Changing almost any attribute of any UI element will break the cache of your canvas. If that happens, we go through most of the process again. These changes, by the way, trigger what is called a canvas rebuild.

I'll give you some examples of the breaking changes: scaling, positioning, rotation, color, image swapping, animations and more.

After exposing the basics, I want to conclude with three practical observations:

• The more elements you have in your Unity Canvas, the more CPU overhead you will have on each canvas rebuild.
• Avoid any kind of changes in UI to avoid canvas rebuilds. If needed, then put dynamic elements in different canvases.
• Canvases are either static or dynamic. Design accordingly.

Level 2 Unity UI Developer: The GPU

Level 2 Unity UI Developer: The GPU

Now is the turn for the friendly Graphical Processing Unit, don't you think?

The GPU is the piece of hardware that makes us fall in love with games. We owe them so much. What about showing it some affection? Well, we can...

By treating it well.

But guess what? UI can make the GPU pretty upset. Especially mobile GPUs, where it is relatively easy to be memory-bound. To put it simply:

In mobile, there is a massive reason UI is expensive: overdraw!

Overdraw happens when we render the same pixel multiple times per frame. And this is soooo easy to achieve with Unity.

Every time to add a Unity UI Image, you are commanding your GPU to draw a full rectangle, rendering every single pixel inside that rectangle. And it does not matter if the pixel you are drawing is transparent, it will cost you still.

That means, I advise you to be careful with the transparent regions of your sprites!

This has some implications for you. If you add 10 full-screen images, then you get 10x overdraw. As my grandmother used to say, WTAIWYG! (What You Add Is What You Get).

Stacking of layers on top of each other will slowly enrage your GPU. It will add milliseconds to it, which is a crime in VR games where your budget could very well be under 13ms.

I do not want to get too technical in this post... but I can't just help it! Some day you will be having a delicious coffee break conversation with your colleagues and you might feel tempted to drop a few intellectual lines. If that's the case, say this one aloud:

UI Overdraw is expensive in mobile because you devour the precious memory bandwidth of the device and this is further worsened by the alpha blending happening internally

You'll make some jaws drop.

The key lesson is easy: avoid stacking UI elements on top of each other and you will be fine 

• GPU cost mainly comes from stacking graphical layers on top of each other. Avoid these.
• Reduce the space UI takes in screen to reduce GPU cost.
• Implement sprite atlasing to improve CPU and GPU performance.

PRO TIP #1: Sprite Atlasing (opens in a new tab)

PRO TIP #2: Opaque UI Shading (opens in a new tab; Advanced)

Level 2 Unity UI Developer: The Developer

Level 2 Unity UI Developer: The Developer!

I am afraid we often under-estimate the effort required to design, implement and especially maintain optimized user interfaces in Unity.

Surely, Unity improved in this area during the last few years and now it is easier and faster than ever to create those. But this comes at a cost.

In general, the more Unity UI extras you use, the worse your game will perform.

The auto-layout helpers are especially expensive. Unfortunately, they are the most helpful. For instance, I find Vertical Layout Groups especially handy when designing responsive UI. These neat scripts help you organize your elements in a manner that is structured and therefore visually appealing.

The problem I see with those is that they incur on a big CPU cost whenever there are canvas rebuilds!

You might be able to get away with UI helpers if your UI is static 99% of the time, but the frame it isn't, you will notice it.

We love working with helpers, but we don't want to ruin our performance. Here's one trick you can try: keep the auto-layout helpers around while designing but disable them all just before saving your scene. By doing this, they will be deactivated for run-time players, but they already did their work for you!

I don't want to disappoint you, so just remember that this auto-layout disabling secret will not work if your UI content is dynamic.

At the end of the day, the more tasks you delegate to Unity, the more work your hardware will have to do.  Find your own balance here! You can start using those helpers but be ready to remove them if you have to.

While optimizing, do the biggest gains for the buck first. Only advance in the ladder of diminishing returns if the profiler tells you that you have to.

For instance, creating sprite atlases is easy and will bring you good fortune. Tweaking graphics to avoid transparent regions, however, is more time-consuming. Lastly, creating your own UI shaders might bring you big gains but at a big cost.

Remember, saving a few microseconds in your game might not be worth if it costs you weeks of your life-time and your application does not need it. This should not be taken as an excuse to never care; optimizations in the future are more expensive than in the present.

• Profile before you optimize
• Keep profiling
• Go for the biggest gains for the buck first

Level 3 Unity UI Developer: The Guru's UI Development Diagram

Level 3 Developer: The Sweet Spots

From the Venn Diagram, you might see several sweet spots where you could find yourself in: Fine-Grained UI Development, Coarse-Grained UI Development, Massive PP and Balance.

They sounded quite obscure to me at the beginning, but then, with time, it all started to make sense to me. Experience brought understanding.

What I still hold true is that, the more tools you know, the better. This is the main way I am able to recognize the subtle patterns in all problems. And, when you recognize the heart of the challenge, you know which tool to take out of your toolbox.

Nothing will help your team more than having a developer possessing both a high-level overview of UI and an eye for detail.

A Level 3 developer would confidently answer important practical questions that only come through experience. I can think of a few that any client could ask you:

• Here's a UI architecture for you. How performant is it?
• What are 3 alternatives I have to optimize this user interface?
• Can you show me numerical proof?
   

You see, I prepared a few Unity examples for you.

The examples you will have access to illustrate each of the UI optimization methods I propose.

Not only that, I analyzed them all so you can feel safe the information is accurate.

Because... do you know what comes after speaking out of our gut feelings? Speaking with certainty, based on real experience.

So, are you serious about becoming a Level 3 Unity UI Developer?

---> Grab Now the Level 3 Guide from my Blog Post.