Snow Shader Tutorial with Unity

Let It Snow! How To Make a Fast Screen-Space Snow Accumulation Shader In Unity

Have you ever wondered how much time does it take to apply snow to all of the textures in your game? Probably a lot of times. We’d like to show you how to create an Image Effect (screen-space shader) that will immediately change the season of your scene in Unity.

3D model house village with trees in the background in Unity

How does it work?

In the images above you can see two screenshots presenting the same scene. The only difference is that in the second one I enabled snow effect on the camera. No changes to any of the textures has been made. How could that be?

The theory is really simple. The assumption is that there should be a snow whenever a rendered pixel’s normal is facing upwards (ground, roofs, etc.) Also there should be a gentle transition between a snow texture and original texture if pixel’s normal is facing any other direction (pine trees, walls).

Getting the required data

For presented effect to work it requires at least two things:

  • Rendering path set to deferred (For some reason I couldn’t get forward rendering to work correctly with this effect. The depth shader was just rendered incorrectly. If you have any idea why that could be, please leave a message in the comments section.)
  • Camera.depthTextureMode set to DepthNormals

Since the second option can be easily set by the image effect script itself, the first option can cause a problem if your game is already using a forward rendering path.

Setting Camera.depthTextureMode to DepthNormals will allow us to read screen depth (how far pixels are located from the camera) and normals (facing direction).

Now if you’ve never created an Image Effect before, you should know that these are build from at least one script and at least one shader. Usually this shader instead of rendering 3D object, renders full-screen image out of given input data. In our case the input data is an image rendered by the camera and some properties set up by the user.

It’s only the basic setup, it will not generate a snow for you. Now the real fun begins…

The shader

Our snow shader should be an unlit shader – we don’t want to apply any light information to it since on screen-space there’s no light. Here’s the basic template:

Note that if you create a new unlit unity shader (Create->Shader->Unlit Shader) you get mostly the same code.

Let’s now focus only on the important part – the fragment shader. First, we need to capture all the data passed by ScreenSpaceSnow script:

Don’t worry if you don’t know why we need all this data yet. I will explain it in detail in a moment.

Finding out where to snow

As I explained before, we’d like to put the snow on surfaces that are facing upwards. Since we’re set up on the camera that is set to generate depth-normals texture, now we are able to access it. For this case there is

in the code. Why is it called that way? You can learn about it in Unity documentation:

Depth textures are available for sampling in shaders as global shader properties. By declaring a sampler called _CameraDepthTexture you will be able to sample the main depth texture for the camera.

_CameraDepthTexture always refers to the camera’s primary depth texture.

Now let’s start with getting the normal:

Unity documentation says that depth and normals are packed in 16 bits each. In order to unpack it, we need to call DecodeDepthNormal as above seen above.

Normals retrieved in this way are camera-space normals. That means that if we rotate the camera then normals’ facing will also change. We don’t want that, and that’s why we have to multiply it by _CamToWorld matrix set in the script before. It will convert normals from camera to world coordinates so they won’t depend on camera’s perspective no more.

In order for shader to compile it has to return something, so I set up the return statement as seen above. To see if our calculations are correct it’s a good idea to preview the result.

RGB Rendering of Camera Space for Unity Shader Tutorial

We’re rendering this as RGB. In Unity Y is facing the zenith by default. That means that green color is showing the value of Y coordinate. So far, so good!

Now let’s convert it to snow amount factor.

We should be using the G channel, of course. Now, this may be enough, but I like to push it a little further to be able to configure bottom and top threshold of the snowy area. It will allow to fine-tune how much snow there should be on the scene.

Snow texture

Snow may not look real without a texture. This is the most difficult part – how to apply a texture on 3D objects if you have only a 2D image (we’re working on screen-space, remember)? One way is to find out the pixel’s world position. Then we can use X and Z world coordinates as texture coordinates.

Now here’s some math that is not a subject of this article. All you need to know is that vpos is a viewport position, wpos is a world position received by multiplying _CamToWorld matrix by viewport position and it’s converted to a valid world position by dividing by the far plane (_ProjectionParams.z). Finally, we’re calculating the snow color using XZ coordinates multiples by _SnowTexScale configurable parameter and far plane to get sane value. Phew…

Unity Snow Texture for Unity3D shader tutorial

Merging it!

It’s time to finally merge it all together!

Here we’re getting the original color and lerping from it to snowColor using snowAmount.

The final touch: let’s set _TopThreshold value to 0.6:

Voila!

Summary

Here’s a full scene result. Looking nice?

Lowpoly Township Set on the Unity Asset Store

Low Poly 3D Snow Village Unity Asset Shader

Feel free to download the shader here and use it in your project!

Scene that has been used as the example in this article comes from Lowpoly Township Set. Inspired by this particular redditor.

Debugging Web Services With Fiddler In Unity

In order to empower your Unity game with useful features like user accounts, leaderboards, achievements, and cloud saves, you are going to need a web service. Of course, you wouldn’t write one on your own, so most probably you’re thinking of using services like GameSparks or App42. If so, you should learn how to debug it.

Having a REST

If you’re not familiar with what REST is, then it’s the best time to acquire new knowledge. It’s not difficult and no, it’s not another language. It’s just an architecture, a set of rules to follow to make a good API. Thanks to REST all API services look very familiar and are easy to learn. Here’s a good place to start.

Now, when you know that REST calls are nothing else but regular HTTP requests, you may find monitoring all the http traffic between your game and web service as very useful. You may want to do this because:

  • This may be the only way to see the client-server communication
  • Client request may not be what you’ve expected it to be
  • Server response may tell you about other things than client library errors
  • Client library may have bugs that can be revealed in this way

Let’s be honest, you will encounter issues. How fast you will deal with them depends on your debugging skills. If there’s a possibility to peek into client-server communication, why you not just do it?

Wireshark?

wireshark

Most people when asked about looking into client-server communication think about Wireshark. It’s the easiest way to get hands on the full communication and while Wireshark does his job very well, I’d like to recommend something else for debugging.

Fiddler!

fiddler

Telerik Fiddler is available for free for Windows and at the time of writing of this article there’s also OS X beta version available.

What makes Fiddler so special? Especially the fact that it debugs your http traffic using build-in tools so easily. It also has a very simple user interface that is easy to understand and use. Requests and responses can be displayed as a raw text or formatted one as JSON or XML if you expect this kind of data to be in there. On top of that you can customize the requests/responses view to see the data that you’re concerned of and you do this without any trouble.

Fiddler inspectors makes debugging experience really pleasant.

Fiddler inspectors makes debugging experience really pleasant.

Do not confuse Fiddler with the packet sniffer. It does not listen to your web interface, instead it installs itself as a default system proxy. It has its pros and cons. By doing that, it can easily decrypt HTTPS communication (yeah!), but on the other side not all applications accept the default system http proxy settings.  One of these applications is…

Unity

Of course by “Unity” I also mean all apps running on Unity engine. I cannot tell for sure why Unity does not work well with Fiddler, but I know how to make it work with it. There’s a great blog post about it written by Bret Bentzinger. The steps go as follows:

Windows

  1. Make sure Unity is not running
  2. Navigate to UNITY_INSTALL_DIR\Editor\Data\Mono\etc\mono\2.0
  3. Edit machine.config file and inside <system.net> add the following:

OS X

  1. Make sure Unity is not running
  2. Locate the Unity application icon
  3. Right-click on it and choose “Show package contents”
  4. Navigate to Contents/Frameworks/mono/etc/mono/2.0
  5. Do step 3 from the Windows instructions

Important: Make sure to undo these changes after you’re done with debugging!

More about Fiddler

Did I help you make your mind? If yes, you might want to see some more learning resources about Fiddler.

Happy debugging!

Should You Install Unity Cache Server on localhost

Should you install Unity Cache Server on localhost?

Do you already know how to use Unity Cache Server? If you’re one of the maniacs trying to optimize every aspect of their development environment, then you most probably do! It’s a great solution for the teams that are working on large projects, especially for mobile devices. But does it make sense to install it for only one person… locally?

How Unity imports assets

The first thing you need to understand is the way Unity imports assets. When you put a file into your Assets folder, Unity executes an asset processor. The textures will be converted to optimal texture format for your target platform: sounds to mp3/ogg (or any other) conversion, models to internal Unity mesh format and so on. Some conversions are done so fast, that you won’t even notice it, but for some it may take enormous amount of time. For instance, processing Android and iOS textures may even take several hours!

This is not an issue if you’re working on a game for a single platform, but usually you are not. For instance, if you’re working on an Android game, most probably you’d like to build an iOS version too. Unfortunately when you switch your target platform, Unity removes previously processed data as you’d never intend to use it again. As a result, switching between multiple platforms may take more time than actual development of your game!

Let’s install Cache Server

Cache Server solves that issue by storing processed assets in the persistent database for later use. If you’re working alone or if your internet connection is not that great, it may be a wise choice to install it locally.

Cache Server is written on the top of NodeJS. If you’re not familiar with this technology, don’t worry. It’s distributed along with cache server zip file, so you don’t even need to install it! (well, I don’t know now why I even mentioned it…)

Now it’s time to get the Cache Server files. These can be found on Team License web page (Team License is now available for everyone). Just click on the download button.

a280306e-a6e8-4ebe-806a-9ff04bd439a3

Unpack the downloaded zip contents in the location where you want to keep your processed asset database. Cache Server by default creates its database in-place, so be prepared to have at least 50 gigabytes of free space on your drive. Now you’re ready to launch it. Go into the CacheServer directory and double-click on RunWin.cmd file. There are appropriate script files for Mac and Linux too.

d4a57c8c-7df2-41ad-824d-881f87cdbfd2

When you see the output like this one, you know that your Cache Server is operational:

f7548b51-d00c-46d0-8afe-be95a1b26bd5

Now, don’t close this command line window! Your cache server works only when it’s open. When closed, you can re-launch it again and your data will be still there, but if it’s not running Unity is not storing anything in it (obviously).

Configuring Unity

Let’s now open Unity preferences. Go into the Cache Server tab, and use localhost as the IP Address.

3fc6f3ce-5cd7-43a8-8a67-6c7a6ea9b3bf

When you see Connection successful message, this means that your Cache Server is fully operational! Now you have to reimport your assets at least once to have it uploaded to the cache server. Later on instead of usual asset importing progress you will be seeing something like this:

using cache server

How long it will take depends only on the speed of your hard drive.

If you’re interested in more information about the Cache Server, you can find it in the official Unity manual. Please also note that Cache Server may require a license different than free (it got a little confusing after latest changes in licensing, so I cannot tell for sure).

7 Ways to Keep Your Unity Project Organized

I saw a person on Quora the other day, asking how programmers are able to write projects that consist of over 10,000 lines of code. When software gets bigger, it is more difficult to maintain and that’s a fact. So here’s the thing – if you don’t keep your project organized, you’re going to have a hard time to keep the pace. Later on, you will find yourself wasting time with a messy project instead of adding new features. This is also true regarding any Unity Project. Here are (in my opinion) the most important tips that will help you with keeping your project organized.

1. Directory Structure

We cannot talk about organization without mentioning organizing project directory structure. Unity gives you a total freedom in that matter, but because of that, it can frequently get really messy. This is the directory structure I personally use:

  • 3rd-Party
  • Animations
  • Audio
    • Music
    • SFX
  • Materials
  • Models
  • Plugins
  • Prefabs
  • Resources
  • Textures
  • Sandbox
  • Scenes
    • Levels
    • Other
  • Scripts
    • Editor
  • Shaders
  1. Do not store any asset files in the root directory. Use subdirectories whenever possible.
  2. Do not create any additional directories in the root directory, unless you really need to.
  3. Be consistent with naming. If you decide to use camel case for directory names and low letters for assets, stick to that convention.
  4. Don’t try to move context-specific assets to the general directories. For instance, if there are materials generated from the model, don’t move them to Materials directory because later you won’t know where these come from.
  5. Use 3rd-Party to store assets imported from the Asset Store. They usually have their own structure that shouldn’t be altered.
  6. Use Sandbox directory for any experiments you’re not entirely sure about. While working on this kind of things, the last thing that you want to care about is a proper organization. Do what you want, then remove it or organize when you’re certain that you want to include it in your project. When you’re working on a project with other people, create your personal Sandbox subdirectory like: Sandbox/JohnyC.

2. Scene hierarchy structure

Next to the project’s hierarchy there’s also scene hierarchy. As before, I will present you a template. You can adjust it to your needs.

  • Management
  • GUI
  • Cameras
  • Lights
  • World
    • Terrain
    • Props
  • _Dynamic

There are several rules you should follow:

  1. All empty objects should be located at 0,0,0 with default rotation and scale.
  2. When you’re instantiating an object in runtime, make sure to put it in _Dynamic – do not pollute the root of your hierarchy or you will find it difficult to navigate through it.
  3. For empty objects that are only containers for scripts, use “@” as prefix – e.g. @Cheats

3. Use prefabs for everything

Prefabs in Unity are not perfect, but they are the best thing you will find to share pre-configured hierarchies of objects. Generally speaking, try to prefab everything that you put on your scenes. You should be able to create a new level from an empty scene just by adding one or more prefabs to it.

The reason why you should use prefabs is that when a prefab changes, all the instances change too. Have 100 levels and want to add a camera effect on all of them? Not a problem! If your camera is a prefab, just add a camera effect to the camera prefab!

Be aware that you cannot have a prefab in another prefab. Use links instead – have a field that requires a prefab to be assigned and make sure to assign it when instance is created. Consider auto-connecting prefab instances in Awake() or OnEnable() when it makes sense.

4. Learn how to use version control system (VCS)

git logoYou may already know something about GIT, Subversion or any other VCS out there. As a matter of fact, “knowing something” is only a small piece of what you may learn. You should focus on learning about important but infrequently used features of VCS of your choice. Why? Mostly because VCS systems are much more powerful that you think, and unfortunately many users are using these as nothing more than a backup and synchronized solutions. For example, did you know that GIT allows you to stash your changes, so you can work on them later without committing anything to your master branch?

Programmers tend to comment out blocks of code in case it’s needed later. Don’t do that! If you’re using VCS learn how to quickly browse previous versions of a file. When you are familiar with it, your code looks a lot nicer without unnecessary block of commented code.

Here’s a nice resource of tips for GIT users: http://gitready.com/

5. Learn to write editor scripts

Unity is a great game engine in the matter of extensibility (see Asset Store). Learn how to write editor scripts and utilize this knowledge. You don’t necessary need to create fancy GUI for your scripts, it can be something simple, as menu entries that are doing something useful. Here are some examples of editor scripts that I have created not so long ago:

  • Google Sheets .csv download – I had a translation spreadsheet saved on Google Drive. It automatically downloaded the newest version as .csv file, so I never had to do it manually.
  • Randomize the position, rotation and size of trees – I had a lot of trees and wanted it to look more like a forest than a grid.
  • Create distribution – Built for specified target, zips all the files and copy to the right place.
  • String replace in the sources – I had several files that contained the application version.

You can learn how to create editor scripts from the official documentation.

6. Learn to program defensively

Have you heard about defensive programming? Wikipedia defines it as follows:

Defensive programming is a form of defensive design intended to ensure the continuing function of a piece of software under unforeseen circumstances. Defensive programming techniques are used especially when a piece of software could be misused.

Generally when you’re writing MonoBehaviours, you should make sure that:

  • All needed references are set
  • All required components are present
  • If you’re using singletons, make sure that they exists
  • If you’re searching for objects and expect to find something, do it as fast as possible
  • Mix-in editor code (ExecuteInEditMode and #if UNITY_EDITOR) to do as many checks as possible before you run the scene

For many of these checks you can use asserts. You should also read A Story of NullPointerException Part 1 and 2.

7. Implement in-editor and/or in-game cheats

After you learn how to write editor script, you should be able to write a set of in-editor cheats. It can work as menu entry that unlocks something (all levels for instance). It’s really easy to create:

Generally you should write cheats that will allow you to:

  • Unlock all levels, characters, items etc
  • Give you immortality
  • Add/subtract values like time, money, coins etc
  • Allow you to see things not meant to be seen by players
  • Anything else that will help you with testing your game

Of course more practical (but harder to write) are in-game cheats. These type of cheats can be executed outside Unity editor, but you have to think how you would like to execute it. See our other article about implementing cheats subsystem controlled by mouse.

Choosing Between Forward or Deferred Rendering Paths in Unity

One of the most important Unity features is the ability to choose a rendering path.  For those who are not very familiar with Unity, choosing (usually) between forward and deferred rendering paths may be something comparable to choosing between “normal”  and “strange looking and something’s broken” rendering methods. To understand better why there is more than one rendering path, first you will need to understand the motivation behind it.

It’s all about lighting

Lights are expensive, mostly because a lot calculations has to be done to find out the valid color of a pixel when there’s a light in range. In Unity lights can be evaluated per-vertex, per-pixel or as Spherical Harmonics (SH). In this article we will talk only about the former two.

pixel vs vertex lighting

In per-pixel lighting, each pixel color is computed individually (as on the left.) You can see that even when I use low-poly sphere for this example, the lighting still makes it look round. If it wasn’t for the edges, it’d be really hard to spot where all the vertices are. Then, there’s per-vertex lighting. It makes one light calculation per vertex. All the other pixels between vertices evaluate the color using regular color blending algorithm (without further light calculations.) This is the cheapest method of lighting and yeah… it looks cheap (if you’re wondering where’s the pixel and vertex lighting switch, it’s hidden in the Light component under Render Mode option. Important option is forces the light to be pixel light, Not Important is vertex light, Auto makes the strongest light a pixel light.)

It’s not a secret that game developers love per-pixel lighting much more than per-vertex lighting. Yet it has a significant downside. Each light causes the additional rendering pass of each object in the range. There’s a limit of four lights that can affect the object. What’s more, there’s also a limit of shadows – based on Unity documentation only one light can have shadows (for some reason I’ve managed to get two shadows in Unity 5.3.4, so I’m not really sure about this one.)

Deferred rendering to the rescue!

There’s a technique that allows you to use as much lights as you want on your scene with keeping the performance at reasonable level. It does not limit the number of shadows and it does not cause additional draw passes if scene objects are within light range (objects casting shadows are exceptions.) It’s called Deferred Shading Rendering Path.

4 lights deferred lighting

Why is it so different? Mostly because most of the models are rendered without lighting calculations and when the scene rendering is nearly done lights are applied to rendered 2D image. Making changes on this stage is usually called doing something in screen-space. Knowing that, we can say lighting in deferred rendering is screen-space. To understand it better, let’s look at the Frame Debugger.

Scene rendering starts with rendering all geometries:

deferred opaque

This is a flat image, so how graphics card will know how to apply lights and shadows? Thanks to the depth buffer! You can think of depth buffer as of another image that is hidden from you and that stores the information about how far from the camera each pixel is located. When represented as image, it may look like this:

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Depth information alone isn’t enough to figure out how light should be applied on the surface. Still, we need at least one more thing – the orientation. Orientation in 3D space is usually represented by normals. The unusual thing is that along with color buffer and depth buffer, there is a buffer with normals!

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How can you tell that these are normals? It’s pretty easy! Just look at the Scene Gizmo.

scene gizmo

Do you see the color resemblance? Red cone (x) points to the left, so do left faces on previous image. Green (y) to the top and blue (z) bottom-right (from this perspective). It all matches the colors of faces from before.

Basing on that information, lights and shadows can be rendered. It really doesn’t matter how many objects there are on your scene. Everything gets done only on the final image.

After lighting pass

After lighting pass

The image above is the result is an inverted version (1 – color) of lighting pass. At the end it is blended with the first opaque image to get the final result.

Which one should I choose?

After reading all of this you may be full of enthusiasm to use the new rendering path, but hold your horses! Deferred rendering is not a remedy for all of the world problems. It has some…

Limitations

It would be too great to be true, wouldn’t it? There are some limitations.

First of all, deferred rendering does not allow us to render semi-transparent objects. That’s because if something semi-transparent exists on the scene, there’s no way to write down depth and normals for objects that is visible through semi-transparent objects and for current object itself. Unity handles this limitation rendering semi-transparent objects using forward rendering path at the end of the whole process. It works quite well, these objects can cast a shadow, but unfortunately they are unable to receive shadows from other objects. They can also cause some unexpected issues, not known when using forward rendering.

The second limitation is the lack of anti-aliasing support. The reason is similar to the issue with semi-transparent objects, but Unity does not try to workaround it in any way. Instead you can use screen-space AA algorithms (image effects), but the visual effect may be less good-looking.

Another limitation is that you can use up to four culling masks. In the documentation you can read:

that is, your culling layer mask must at least contain all layers minus four arbitrary layers, so 28 of the 32 layers must be set. Otherwise you will get graphical artifacts.

And finally there’s no support for the Mesh Renderer’s Receive Shadows flag.

Requirements

If that’s not enough, deferred rendering works only on a limited set of graphics cards. When it comes to PCs, you can safely assume that all graphics cards not older than 10 years will support it. When it comes to mobile devices, you should assume nothing. But that’s not a big issue, because…

Performance

The most important thing is that deferred rendering in most cases will get a worse performance on mobile devices than forward rendering. It’s because of additional passes that need to be done on each frame. If you’re using only one light, then it may not be worth it.

On the other hand, adding extra lights is quite cheap. In the worst case scenario performance will drop linearly and compared to forward lighting, it’s independent of number of objects on the scene.

Cities: Skylines (done in Unity) decided to use deferred rendering path. There's a lot of small lights in this game and it still performs really well.

Cities: Skylines (made with Unity) decided to use deferred rendering path. There’s a lot of small lights in this game and it still performs really well.

Resources

I hope that this article will cast some light on what rendering path you should choose for your game. Anyway, you may also be interested in these resources: