This is part of a series of posts revolving around user interface design and development, the introduction and links to the other posts can be found here.
During the development of our current game I’ve been tackling the user interface. This post outlines some issues involved with creating a pixel perfect scalable user interface that also handles the different aspect ratios whilst maintaining a consistent look and feel. (A bit of a mouthful, right?). Some of the article will be specific to Unity as this is our current development engine but, hopefully, even if you’re not using Unity you’ll be able to take something useful away.
Libraries vs. Bespoke
The first decision that will affect your ability to achieve the best possible UI will be a typical development question.
Shall I use a library or build my own?
Each development team approach this question differently but there are some key points to consider. There is the usual trade off between how big your budget is, how many developers are involved on the project and how long the project schedule is. Even if you can afford to dedicate a developer for a few months to develop a custom UI system from scratch, is that really the best use of their time and your money? I’d say it usually isn’t unless you’re planning a lot of revolutionary features that none of the existing libraries provide. This usually isn’t the case.
Now I’ll play devil’s advocate. If you decide to go with a library, what about the features, maintenance, extendibility and future roadmap? Is there much use using a library that you can’t extend or fix yourself? What if the updates are released further and further apart? Those aren’t ideal situations so each of these points are worth some consideration. Any one of them might have a major impact on your game.
For us, a two person team, building our own UI system just isn’t viable. It would take a single developer many months of full time development to achieve the functionality that is available in existing libraries. In our case we’re happy with functionality provided by some UI libraries, however, we made sure that the source code was available in case we ever wanted to branch development.
Vector vs. Raster (Bitmap)
When selecting or building a UI system a choice will need to be made on what image format will be used. Will the system support vector, raster or both? For this article I’ll assume the difference between vector and raster is known but if not there is a summary here.
There seems to be some debate on whether to use of a vector or raster based UI system. When digging deeper into developer’s preferences two Twitter conversations lead to the following comments.
You mean something like Scaleform? Too expensive. NGUI (on which uGUI is based) does a perfect job, if you do it right.
Smart UI dev tries to be resolution independent, supports various aspect ratios. With vector based UI, it’s not a problem.
The split in opinion comes from the fact that there isn’t a clear right or wrong choice and there very rarely is in software development. Both vector and raster based UI systems have their advantages and disadvantages independent of the file format itself. Straying into Unity specific libraries I’ll try to highlight the differences between the two systems.
Raster System (Daikon Forge, NGUI, uGUI)
The raster based libraries that exist for Unity are almost entirely drag and drop or wizard based. This makes for a very designer friendly approach, especially if the designer has limited to no programming experience. Some programmers may become frustrated with such approaches though.
Good: Better effects & depth
Raster art tends to have a much wider range of effects that can be created and applied to them compared to vector art. Very often original files that start out as vectors will eventually be rasterised so effects and textures can be applied to them to give them more depth and smooth blends in colour.
Good: Source code provided
Most, if not all, of the raster libraries provide their source code. This is an extremely important point that cannot be overemphasised. As a general rule of thumb, developers should stay away from making any local edits to a library they are using, however, there will usually be situations where a change will need to be made. With the source code this isn’t a problem but care must be taken to port the change to later versions of the library. Without the source code this turns into a big issue that slows development down and, in the worst case situation, can lead to replacing the library.
Bad: Pixel perfect scaling issues
Pixel perfect scaling for raster libraries can be a real pain. When using libraries like Daikon Forge and NGUI you’re able to turn pixel perfect on by a click of a checkbox, however, this won’t scale yet. You’ll need to combine this with anchors to ensure that the position is correct. It can take a bit of playing to get things right from my experience.
Why do you want a scaled pixel perfect UI? Without being pixel perfect you’ll have a blurry interface on anything except the designed for aspect ratio and resolution. Without scaling then the UI will seem too small or large depending on the resolution being used vs. the designed resolution.
If you are developing a game for mobile and desktop platforms then alternative images may be required for different devices based on resolution requirements. If this is the case then it’s common for sprite atlas and texture swapping to be taken into account.
Bad: Aspect ratio issues
Things tend to get worse when scaling with aspect ratios. Your UI design may be thrown completely out the window if you haven’t taken care to incorporate the supported aspect ratios. A major problem with this is UI stretching. For example, making use of anchors to achieve a scaling UI designed for a 4:3 ratio will cause a lot of stretching when playing in a 16:9 resolution unless a lot of care is taken.
Anchor systems differ considerably from Daikon Forge and NGUI (NGUI v2 and the new NGUI v3+ anchors) and in our case we developed custom anchors to help fill the gaps in functionality.
Vector System (Scaleform, NoesisGUI)
The vector based libraries that exist for Unity are a mixture of third party tool designer based and pure code based systems. A more code based approach may appeal to some developers more than a designer based approach so it’s something to consider along with the following points.
Good: Pixel perfect scaling
The better vector based libraries will handle runtime vector loading instead of buildtime vector loading. This means scaling will always be pixel perfect with very little effort on the developer. Compared to raster libraries this could save a fair amount of time and effort. Aspect ratios are still a problem but removing pixel perfect scaling from the situation makes things easier.
Good: Image sizes
Vector art have smaller file sizes than raster art due to vectors being mathematical formula based. If building a game for a platform that has limited file system space or there is a requirement to keep final build size as low as possible then a vector based system will help. Generally it won’t help in terms of memory usage as the vector art will use more memory the more complex it is and it tends to effectively draw a bitmap based off the vector data.
Bad: More expensive in price
If using a Unity library for vector UI then the prices are generally at least twice as much as the next best raster based UI library. The libraries are around the range of £250 so, for a business, this isn’t too much in reality. If your budget can cover this then it’s not a problem.
Bad: Closed source code
As explained above, not having the source code for a library can cause some major problems later in the development process. You’ll usually find the source code is available for these libraries but it’s usually for a large cost and must be negotiated for.
Bad: Cross-platform support issues
Support for multiple platforms, especially Linux, tends to be lacking. Devices like Oculus Rift aren’t supported and NoesisGUI doesn’t support consoles yet.
Neutral: Third party tools for designing layout
Scaleform uses Adobe Flash Studio (and I think a few other tools support it too) for designing the UI and this leads to a flash based UI.
NoesisGUI uses XAML and this can be hand coded or designed using Visual Studio.
While these two points aren’t really bad it does lead to reliance on more tools, some of which you have to pay for. If taking the XAML route then this isn’t a problem as you can hand code the design (or visually design it in Visual Studio) then view the UI in Noesis’ viewer. It’s just more points to be aware of.
So, as you can see there is no real right or wrong choice (or at least that’s my opinion). Whether you develop a bespoke system or use one of the two types of libraries, make sure it matches you and your team’s approach, resources and requirements.
For the next article I’ll go into what UI framework we chose and how we addressed the problems and questions raised above. If you have any questions, want to debate or just to share your experiences – grab me on Twitter at @CWolf.
Thanks for reading! 🙂
April 23, 2014 at 11:15 am
Good read, well done!