Tag Archives: Class

Scene Transition/Screen Fader Tutorial Part 2

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Welcome to part two of my screen fader tutorial. In this part I will provide a short demonstration of how you might use the screen fader to smoothly transition between scenes.

I’ll add two scenes to the project, with different title text and background colour, so it’s obvious when the scene has changed, and a single button in the middle of the screen which will be used to make the scene change.

I’ve added a small script to the button, which exposes an Object property to the editor, into which I drag the scene that I would like the button to load when clicked. Note: any scenes that are to be loaded at runtime must be added to the build settings in the editor.
Build Settings

This button script is how an inexperienced Unity programmer might approach it, but it won’t work properly and if you try it you’ll see that the scene change happens immediately with no fade in or out.

The reason for that is that as soon as the fade out function is called Unity moves immediately onto the next line of code and executes it, this stops the fade out and loads the next scene. It then goes on to start the fade in function, which has no effect as the screen isn’t faded out.

So how do we prevent execution of the line after the fade out call until we are ready for it? One way would be with coroutines, but this can easily get messy and means that we can’t keep all our code in one function. So this is where the callback argument of the fadein/fadeout functions comes into play.

With the above in mind we could write our button code like this instead:-

So now we have separated the fadeout function call from the load scene and fadein function calls, and put them in a separate function. We have then provided the new function as the callback argument for the fadeout routine.

Now if you run the program and click the button you’ll see that it works exactly as it should, the original screen fades out, and then the new scene smoothly fades into view.
This is because now the fadeout routine is executing and only when it’s finished does it invoke the callback function which loads the new scene and fades it back in.

This is much better, in as much as it actually works. However earlier I mentioned that a disadvantage of using coroutines to achieve the same was that we couldn’t contain everything in one function, and you’ll probably have noticed by now that this solution suffers from the same problem.

We can fix that however by writing the callback function inline in the fadout function call, this isn’t strictly speaking necessary, but in a lot of instances it can keep the code simpler and easier to follow in my opinion.

So this is the final version of the button script:-

As you can see the whole process is now contained within a single 7 line script, with execution of the scene change and fadein delayed until the fadeout function has finished. I’ve also added a 0.5f second delay to the fadein function call as I think it looks better with a slight extra delay.

That’s it for this tutorial, as always any and all comments or suggestions are welcome. See you next time.

Unity project file

Scene Transition/Screen Fader Tutorial Part1

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A common feature of games is that the screen briefly fades to black during scene changes. This is done to ‘soften’ the transition as a sudden switch from one scene to another can be a bit jarring if it’s visible when it happens.

So I’ve found it handy to have a screen fader that I can easily drop in to a new project any time I want to have fade to black (or some other colour) scene transitions and I decided that it would be a nice subject for a mini tutorial. It will also serve to demonstrate a couple of seemingly often overlooked but very useful features, i.e. callbacks and CanvasGroups.

The aim of this tutorial will be to provide a screen fader that is fairly simple to implement and is also flexible and easy to use.

The way this screen fader will work is by overlaying a UI image on the screen and changing it’s alpha value to fade it in and out.

To make it as easy as possible to add to a project, we’ll have the fader create its own UI elements in code, which means all we have to do is drop the screen fader script onto an empty game objet to make it available for us to use. To make this work we’ll need the screen fader to create its own Canvas, CanvasGroup component and an Image.

Step 1)
This is the code to create the Canvas at runtime:-

What this does is create a new GameObject with a Canvas component attached. It then parents it to the GameObject that script is on, then it sets the RenderMode to ScreenSpace overlay and sets the sort order to the value specified in the inspector (default 99). I have made the sort order easy to change so that you can make sure the fader image is always on top of everything else. However depending on what you wanted you could also use the sort order to have it appear behind some elements.)

Step 2)
This is the code to create the CanvasGroup at runtime:-

We use AddComponent() to add the CanvasGroup component to the canvas we just created, and then store, in a member variable, the reference to the component that it returns for later use. Then we set interactable and blocksraycasts to false, which means that any child objects of the canvas group won’t block mouse clicks. This isn’t strictly necessary for our purposes here, and indeed in some instances you may want your screen fader to block input, in which case you would set interactable and blocksraycasts to true.
Lastly we disable the GameObject as we don’t need to have it enabled until we are ready to use it.

Step 3)
This is the code to create the Image at runtime:-

Firstly we create a new GameObject with an Image Component attached, then we set it as a child of the canvas we created in step 1. Next we set its colour to the value specified in the inspector (default black), and lastly scale it up a bit, this last bit is done to prevent a slight border appearing around the edges in some screen resolutions.

Step 4)
Set the image position and size and make it scale with the screen size:-

The easiest way to change position and size of ScreenSpace UI elements is to use the RectTransform component, so firstly we get a reference to the Image RectTransform using GetComponent().

Next we set the anchors to the bottom left and top right to make the image stretch with the screen size. The anchors are Vector2s with values between 0,0 and 1,1, where 0,0 is the bottom left of the screen and 1,1 is the top right of the screen.
Next we centre the image by setting its anchoredPosition to 0,0;
Lastly we set the width and height to match the current screen size (due to the scaling we did in step 3, it will be slightly larger than the screen).

Now we need to put all of that above into the Awake function of the screen saver. This is the complete Awake() function.

The only part of the Awake() function I haven’t discussed yet is the very first block of code. Basically what this does is make the screen fader not get destroyed during scene changes, and also ensures that the only instance of it that can exist is the first one that is created. It also grabs a static reference to the first instance so that it is possible to access non static methods and properties.

That’s the basic setup finished, so next we’ll define a couple of static methods that will enable us to perform fade outs and fade ins. The methods will invoke callbacks when finished so that we can delay execution of other code whilst the fader is in operation. We will also be able to specify a delay before and/or after the screen fade.

This is the public static method to do a fade out:-

As you can see it is quite simple, all it does is check to see if the callback argument is null, and if so it points it to the default empty callback function and then it sets the canvas active.
Next it stops any current fade in/out operations (I’ll discuss that function further on) and runs the fade out coroutine, which is where most of the work is done.
It uses the variant of StartCoroutine that returns a CoRoutine object, which we store for use by the StopActiveFades() function.

This is the code for the fade out coroutine:-

There again, this is quite straightforward, first of all we yield wait for the delayBefore period.
Then we loop while the group.alpha property is less then 1. The alpha property controls the transparency of all children of the group (in this instance our image we created in step 3), a value of zero means fully transparent and a value of one means fully opaque.

In the while loop we use MathF.MoveTowards to linearly fade from transparent to opaque, we can use the speed property in the inspector to control how quickly this happens.
After the while loop exits we yield wait for the delayAfter period if any, and then we invoke the callback to signal that the fade is done.

The fade in functions are almost identical, except in the while loop we change the group.alpha from one to zero and when it’s finished it disables the canvas.

Now let’s take a look at the StopActiveFades() function:-

This function just ensures that there can’t be two fade operations running at the same time, as that could result in unwanted behaviour.
What it does is check the fadeInCR and fadeOutCR variables and if they aren’t null it stops the coroutine they point to and sets the variable to null.

Last of all is the default empty callback function, which doesn’t need any explanation.

In the next part of this tutorial I will show how we can use the screen fader in our applications, but in the meantime here is the full screen fader script:-

As always any and all comments are welcome, see you next time.

Generic Serialiser Class

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It’s been a busy month what with one thing and another, so I haven’t managed to get finished the UNET custom NetworkHUD tutorial I’ve been working on, but I’ll post it as soon as I can.

In the meantime I’ve been doing some groundwork for an RPG idea we’ve had, and one of the first requirements is for an easy way to save and load the state of the various data classes we’ll be using. As this is something that also seems to get asked for on a fairly regular basis in the forums, I thought I’d share what I’ve come up with so far as it might prove useful to others in some situations.

The serialiser as it currently stands is quite simple, it has four static methods, two for serialising the data (one to PlayerPrefs and one as binary data), and two that read in the data and return it in an instance of the corresponding class.
It will serialise any class or struct that is marked as Serialisable and it even works with dictionaries.

This is the code for the serialiser class.

As an example, to save the state of a class to PlayerPrefs you would use something like this:-

To load the data back into the program you would use something like this:-

The way I actually tend to use it though is to wrap the serialiser calls into two methods on the class I want to serialise. An instance method for saving, and a static method for loading the data, which returns an instance of the class populated with the data.

So for example, i might define a PlayerInfo class something like this:-

And then from elsewhere in the program I would load and save the class data like so:-

The Load() function automatically handles the situation where there is no saved data yet, and returns a new instance of the class in that case.

I have made a simple demonstration program that allows you to type in a player name and add and remove items from the inventory. When you exit and restart the program you will see that the changes you made will have been preserved.

Using this generic serialiser it becomes a simple task to save and load even quite complex classes and structs, as long as you remember to mark them as serialisable.

Also remember that if you make any changes to the serialised class definition after you have saved it, you will most likely have to delete the saved data to avoid errors when it tries to load it next.

I hope this proves to be of use to someone, and as always any comments and suggestions are welcome.

You can try out the test program in a Unity WebPlayer here or download the project files here.

See you soon

Martin.