In this article by Nitish Misra, author of the book, Learning Unreal Engine Android Game Development, mentions about the Blueprint class. You would need to do all the scripting and everything else only once. A Blueprint class is an entity that contains actors (static meshes, volumes, camera classes, trigger box, and so on) and functionalities scripted in it. Looking at our example once again of the lamp turning on/off, say you want to place 10 such lamps. With a Blueprint class, you would just have to create and script once, save it, and duplicate it. This is really an amazing feature offered by UE4.
(For more resources related to this topic, see here.)
Creating a Blueprint class
To create a Blueprint class, click on the Blueprints button in the Viewport toolbar, and in the dropdown menu, select New Empty Blueprint Class. A window will then open, asking you to pick your parent class, indicating the kind of Blueprint class you wish to create.
At the top, you will see the most common classes. These are as follows:
Actor: An Actor, as already discussed, is an object that can be placed in the world (static meshes, triggers, cameras, volumes, and so on, all count as actors)
Pawn: A Pawn is an actor that can be controlled by the player or the computer
Character: This is similar to a Pawn, but has the ability to walk around
Player Controller: This is responsible for giving the Pawn or Character inputs in the game, or controlling it
Game Mode: This is responsible for all of the rules of gameplay
Actor Component: You can create a component using this and add it to any actor
Scene Component: You can create components that you can attach to other scene components
Apart from these, there are other classes that you can choose from. To see them, click on All Classes, which will open a menu listing all the classes you can create a Blueprint with. For our key cube, we will need to create an Actor Blueprint Class. Select Actor, which will then open another window, asking you where you wish to save it and what to name it. Name it Key_Cube, and save it in the Blueprint folder. After you are satisfied, click on OK and the Actor Blueprint Class window will open.
The Blueprint class user interface is similar to that of Level Blueprint, but with a few differences. It has some extra windows and panels, which have been described as follows:
Components panel: The Components panel is where you can view, and add components to the Blueprint class. The default component in an empty Blueprint class is DefaultSceneRoot. It cannot be renamed, copied, or removed. However, as soon as you add a component, it will replace it. Similarly, if you were to delete all of the components, it will come back. To add a component, click on the Add Component button, which will open a menu, from where you can choose which component to add. Alternatively, you can drag an asset from the Content Browser and drop it in either the Graph Editor or the Components panel, and it will be added to the Blueprint class as a component. Components include actors such as static or skeletal meshes, light actors, camera, audio actors, trigger boxes, volumes, particle systems, to name a few. When you place a component, it can be seen in the Graph Editor, where you can set its properties, such as size, position, mobility, material (if it is a static mesh or a skeletal mesh), and so on, in the Details panel.
Graph Editor: The Graph Editor is also slightly different from that of Level Blueprint, in that there are additional windows and editors in a Blueprint class. The first window is the Viewport, which is the same as that in the Editor. It is mainly used to place actors and set their positions, properties, and so on. Most of the tools you will find in the main Viewport (the editor's Viewport) toolbar are present here as well.
Event Graph: The next window is the Event Graph window, which is the same as a Level Blueprint window. Here, you can script the components that you added in the Viewport and their functionalities (for example, scripting the toggling of the lamp on/off when the player is in proximity and moves away respectively). Keep in mind that you can script the functionalities of the components only present within the Blueprint class. You cannot use it directly to script the functionalities of any actor that is not a component of the Class.
Construction Script: Lastly, there is the Construction Script window. This is also similar to the Event Graph, as in you can set up and connect nodes, just like in the Event Graph. The difference here is that these nodes are activated when you are constructing the Blueprint class. They do not work during runtime, since that is when the Event Graph scripts work. You can use the Construction Script to set properties, create and add your own property of any of the components you wish to alter during the construction, and so on.
Let's begin creating the Blueprint class for our key cubes.
Viewport
The first thing we need are the components. We require three components: a cube, a trigger box, and a PostProcessVolume. In the Viewport, click on the Add Components button, and under Rendering, select Static Mesh. It will add a Static Mesh component to the class. You now need to specify which Static Mesh you want to add to the class. With the Static Mesh actor selected in the Components panel, in the actor's Details panel, under the Static Mesh section, click on the None button and select TemplateCube_Rounded. As soon as you set the mesh, it will appear in the Viewport. With the cube selected, decrease its scale (located in the Details panel) from 1 to 0.2 along all three axes.
The next thing we need is a trigger box. Click on the Add Component button and select Box Collision in the Collision section. Once added, increase its scale from 1 to 9 along all three axes, and place it in such a way that its bottom is in line with the bottom of the cube.
The Construction Script
You could set its material in the Details panel itself by clicking on the Override Materials button in the Rendering section, and selecting the key cube material. However, we are going to assign its material using Construction Script. Switch to the Construction Script tab. You will see a node called Construction Script, which is present by default. You cannot delete this node; this is where the script starts. However, before we can script it in, we will need to create a variable of the type Material. In the My Blueprint section, click on Add New and select Variable in the dropdown menu. Name this variable Key Cube Material, and change its type from Bool (which is the default variable type) to Material in the Details panel. Also, be sure to check the Editable box so that we can edit it from outside the Blueprint class.
Next, drag the Key Cube Material variable from the My Blueprint panel, drop it in the Graph Editor, and select Set when the window opens up. Connect this to the output pin of the Construction Script node. Repeat this process, only this time, select Get and connect it to the input pin of Key Cube Material.
Right-click in the Graph Editor window and type in Set Material in the search bar. You should see Set Material (Static Mesh). Click on it and add it to the scene. This node already has a reference of the Static Mesh actor (TemplateCube_Rounded), so we will not have to create a reference node. Connect this to the Set node. Finally, drag Key Cube Material from My Blueprint, drop it in the Graph Editor, select Get, and connect it to the Material input pin. After you are done, hit Compile. We will now be able to set the cube's material outside of the Blueprint class.
Let's test it out. Add the Blueprint class to the level. You will see a TemplateCube_Rounded actor added to the scene. In its Details panel, you will see a Key Cube Material option under the Default section. This is the variable we created inside our Construction Script. Any material we add here will be added to the cube. So, click on None and select KeyCube_Material. As soon as you select it, you will see the material on the cube. This is one of the many things you can do using Construction Script. For now, only this will do.
The Event Graph
We now need to script the key cube's functionalities. This is more or less the same as what we did in the Level Blueprint with our first key cube, with some small differences. In the Event Graph panel, the first thing we are going to script is enabling and disabling input when the player overlaps and stops overlapping the trigger box respectively. In the Components section, right-click on Box. This will open a menu. Mouse over Add Event and select Add OnComponentBeginOverlap. This will add a Begin Overlap node to the Graph Editor. Next, we are going to need a Cast node. A Cast node is used to specify which actor you want to use. Right-click in the Graph Editor and add a Cast to Character node. Connect this to the OnComponentBeginOverlap node and connect the other actor pin to the Object pin of the Cast to Character node. Finally, add an Enable Input node and a Get Player Controller node and connect them as we did in the Level Blueprint.
Next, we are going to add an event for when the player stops overlapping the box. Again, right-click on Box and add an OnComponentEndOverlap node. Do the exact same thing you did with the OnComponentBeginOverlap node; only here, instead of adding an Enable Input node, add a Disable Input node. The setup should look something like this:
You can move the key cube we had placed earlier on top of the pedestal, set it to hidden, and put the key cube Blueprint class in its place. Also, make sure that you set the collision response of the trigger actor to Ignore.
The next step is scripting the destruction of the key cube when the player touches the screen. This, too, is similar to what we had done in Level Blueprint, with a few differences. Firstly, add a Touch node and a Sequence node, and connect them to each other. Next, we need a Destroy Component node, which you can find under Components | Destroy Component (Static Mesh). This node already has a reference to the key cube (Static Mesh) inside it, so you do not have to create an external reference and connect it to the node. Connect this to the Then 0 node.
We also need to activate the trigger after the player has picked up the key cube. Now, since we cannot call functions on actors outside the Blueprint class directly (like we could in Level Blueprint), we need to create a variable. This variable will be of the type Trigger Box. The way this works is, when you have created a Trigger Box variable, you can assign it to any trigger in the level, and it will call that function to that particular trigger. With that in mind, in the My Blueprint panel, click on Add New and create a variable. Name this variable Activated Trigger Box, and set its type to Trigger Box. Finally, make sure you tick on the Editable box; otherwise, you will not be able to assign any trigger to it. After doing that, create a Set Collision Response to All Channels node (uncheck the Context Sensitive box), and set the New Response option to Overlap. For the target, drag the Activated Trigger Box variable, drop it in the Graph Editor, select Get, and connect it to the Target input.
Finally, for the Post Process Volume, we will need to create another variable of the type PostProcessVolume. You can name this variable Visual Indicator, again, while ensuring that the Editable box is checked. Add this variable to the Graph Editor as well. Next, click on its pin, drag it out, and release it, which will open the actions menu. Here, type in Enabled, select Set Enabled, and check Enabled. Finally, add a Delay node and a Destroy Actor and connect them to the Set Enabled node, in that order. Your setup should look something like this:
Back in the Viewport, you will find that under the Default section of the Blueprint class actor, two more options have appeared: Activated Trigger Box and Visual Indicator (the variables we had created). Using this, you can assign which particular trigger box's collision response you want to change, and which exact post process volume you want to activate and destroy. In front of both variables, you will see a small icon in the shape of an eye dropper. You can use this to choose which external actor you wish to assign the corresponding variable. Anything you scripted using those variables will take effect on the actor you assigned in the scene. This is one of the many amazing features offered by the Blueprint class. All we need to do now for the remaining key cubes is:
Place them in the level
Using the eye dropper icon that is located next to the name of the variables, pick the trigger to activate once the player has picked up the key cube, and which post process volume to activate and destroy.
In the second room, we have two key cubes: one to activate the large door and the other to activate the door leading to the third room. The first key cube will be placed on the pedestal near the big door. So, with the first key cube selected, using the eye dropper, select the trigger box on the pedestal near the big door for the Activated Trigger Box variable. Then, pick the post process volume inside which the key cube is placed for the Visual Indicator variable.
The next thing we need to do is to open Level Blueprint and script in what happens when the player places the key cube on the pedestal near the big door. Doing what we did in the previous room, we set up nodes that will unhide the hidden key cube on the pedestal, and change the collision response of the trigger box around the big door to Overlap, ensuring that it was set to Ignore initially.
Test it out! You will find that everything is working as expected. Now, do the same with the remaining key cubes. Pick which trigger box and which post process volume to activate when you touch on the screen. Then, in the Level Blueprint, script in which key cube to unhide, and so on (place the key cubes we had placed earlier on the pedestals and set it to Hidden), and place the Blueprint class key cube in its place.
This is one of the many ways you can use Blueprint class. You can see it takes a lot of work and hassle. Let us now move on to Artificial intelligence.
Scripting basic AI
Coming back to the third room, we are now going to implement AI in our game. We have an AI character in the third room which, when activated, moves. The main objective is to make a path for it with the help of switches and prevent it from falling. When the AI character reaches its destination, it will unlock the key cube, which the player can then pick up and place on the pedestal. We first need to create another Blueprint class of the type Character, and name it AI_Character. When created, double-click on it to open it. You will see a few components already set up in the Viewport. These are the CapsuleComponent (which is mainly used for collision), ArrowComponent (to specify which side is the front of the character, and which side is the back), Mesh (used for character animation), and CharacterMovement. All four are there by default, and cannot be removed. The only thing we need to do here is add a StaticMesh for our character, which will be TemplateCube_Rounded.
Click on Add Components, add a StaticMesh, and assign it TemplateCube_Rounded (in its Details panel). Next, scale this cube to 0.2 along all three axes and move it towards the bottom of the CapsuleComponent, so that it does not float in midair.
This is all we require for our AI character. The rest we will handle in Level Blueprints. Next, place AI_Character into the scene on the Player side of the pit, with all of the switches. Place it directly over the Target Point actor.
Next, open up Level Blueprint, and let's begin scripting it. The left-most switch will be used to activate the AI character, and the remaining three will be used to draw the parts of a path on which it will walk to reach the other side.
To move the AI character, we will need an AI Move To node. The first thing we need is an overlapping event for the trigger over the first switch, which will enable the input, otherwise the AI character will start moving whenever the player touches the screen, which we do not want. Set up an Overlap event, an Enable Input node, and a Gate event. Connect the Overlap event to the Enable Input event, and then to the Gate node's Open input.
The next thing is to create a Touch node. To this, we will attach an AI Move To node. You can either type it in or find it under the AI section. Once created, attach it to the Gate node's Exit pin.
We now need to specify to the node which character we want to move, and where it should move to. To specify which character we want to move, select the AI character in the Viewport, and in the Level Blueprint's Graph Editor, right-click and create a reference for it. Connect it to the Pawn input pin. Next, for the location, we want the AI character to move towards the second Target Point actor, located on the other side of the pit. But first, we need to get its location in the world. With it selected, right-click in the Graph Editor, and type in Get Actor Location. This node returns an actor's location (coordinates) in the world (the one connected to it). This will create a Get Actor Location, with the Target Point actor connect to its input pin.
Finally, connect its Return Value to the Destination input of the AI Move To node.
If you were to test it out, you would find that it works fine, except for one thing: the AI character stops when it reaches the edge of the pit. We want it to fall off the pit if there is no path. For that, we will need a Nav Proxy Link actor. A Nav Proxy Link actor is used when an AI character has to step outside the Nav Mesh temporarily (for example, jump between ledges). We will need this if we want our AI character to fall off the ledge. You can find it in the All Classes section in the Modes panel. Place it in the level.
The actor is depicted by two cylinders with a curved arrow connecting them. We want the first cylinder to be on one side of the pit and the other cylinder on the other side. Using the Scale tool, increase the size of the Nav Proxy Link actor.
When placing the Nav Proxy Link actor, keep two things in mind:
Make sure that both cylinders intersect in the green area; otherwise, the actor will not work
Ensure that both cylinders are in line with the AI character; otherwise, it will not move in a straight line but instead to where the cylinder is located
Once placed, you will see that the AI character falls off when it reaches the edge of the pit. We are not done yet. We need to bring the AI character back to its starting position so that the player can start over (or else the player will not be able to progress). For that, we need to first place a trigger at the bottom of the pit, making sure that if the AI character does fall into it, it overlaps the trigger. This trigger will perform two actions: first, it will teleport the AI character to its initial location (with the help of the first Target Point); second, it will stop the AI Move To node, or it will keep moving even after it has been teleported.
After placing the trigger, open Level Blueprint and create an Overlap event for the trigger box. To this, we will add a Sequence node, since we are calling two separate functions for when the player overlaps the trigger. The first node we are going to create is a Teleport node. Here, we can specify which actor to teleport, and where. The actor we want to teleport is the AI character, so create a reference for it and connect it to the Target input pin. As for the destination, first use the Get Actor Location function to get the location of the first Target Point actor (upon which the AI character is initially placed), and connect it to the Dest Location input.
To stop the AI character's movement, right-click anywhere in the Graph Editor, and first uncheck the Context Sensitive box, since we cannot use this function directly on our AI character. What we need is a Stop Active Movement node. Type it into the search bar and create it. Connect this to the Then 1 output node, and attach a reference of the AI character to it. It will automatically convert from a Character Reference into Character Movement component reference.
This is all that we need to script for our AI in the third room. There is one more thing left: how to unlock the key cube.
In the fourth room, we are going to use the same principle. Here, we are going to make a chain of AI Move To nodes, each connected to the previous one's On Success output pin. This means that when the AI character has successfully reached the destination (Target Point actor), it should move to the next, and so on. Using this, and what we have just discussed about AI, script the path that the AI will follow.
Packaging the project
Another way of packaging the game and testing it on your device is to first package the game, import it to the device, install it, and then play it. But first, we should discuss some settings regarding packaging, and packaging for Android.
The Maps & Modes settings
These settings deal with the maps (scenes) and the game mode of the final game. In the Editor, click on Edit and select Project settings. In the Project settings, Project category, select Maps & Modes.
Let's go over the various sections:
Default Maps: Here, you can set which map the Editor should open when you open the Project. You can also set which map the game should open when it is run. The first thing you need to change is the main menu map we had created. To do this, click on the downward arrow next to Game Default Map and select Main_Menu.
Local Multiplayer: If your game has local multiplayer, you can alter a few settings regarding whether the game should have a split screen. If so, you can set what the layout should be for two and three players.
Default Modes: In this section, you can set the default game mode the game should run with. The game mode includes things such as the Default Pawn class, HUD class, Controller class, and the Game State Class. For our game, we will stick to MyGame.
Game Instance: Here, you can set the default Game Instance Class.
The Packaging settings
There are settings you can tweak when packaging your game. To access those settings, first go to Edit and open the Project settings window. Once opened, under the Project section click on Packaging.
Here, you can view and tweak the general settings related to packaging the project file. There are two sections: Project and Packaging. Under the Project section, you can set options such as the directory of the packaged project, the build configuration to either debug, development, or shipping, whether you want UE4 to build the whole project from scratch every time you build, or only build the modified files and assets, and so on.
Under the Packaging settings, you can set things such as whether you want all files to be under one .pak file instead of many individual files, whether you want those .pak files in chunks, and so on. Clicking on the downward arrow will open the advanced settings.
Here, since we are packaging our game for distribution check the For Distribution checkbox.
The Android app settings
In the preceding section, we talked about the general packaging settings. We will now talk about settings specific to Android apps. This can be found in Project Settings, under the Platforms section. In this section, click on Android to open the Android app settings.
Here you will find all the settings and properties you need to package your game. At the top the first thing you should do is configure your project for Android. If your project is not configured, it will prompt you to do so (since version 4.7, UE4 automatically creates the androidmanifest.xml file for you). Do this before you do anything else. Here you have various sections. These are:
APKPackaging: In this section, you can find options such as opening the folder where all of the build files are located, setting the package's name, setting the version number, what the default orientation of the game should be, and so on.
Advanced APKPackaging: This section contains more advanced packaging options, such as one to add extra settings to the .apk files.
Build: To tweak settings in the Build section, you first need the source code which is available from GitHub. Here, you can set things like whether you want the build to support x86, OpenGL ES2, and so on.
Distribution Signing: This section deals with signing your app. It is a requirement on Android that all apps have a digital signature. This is so that Android can identify the developers of the app. You can learn more about digital signatures by clicking on the hyperlink at the top of the section. When you generate the key for your app, be sure to keep it in a safe and secure place since if you lose it you will not be able to modify or update your app on Google Play.
Google Play Service: Android apps are downloaded via the Google Play store. This section deals with things such as enabling/disabling Google Play support, setting your app's ID, the Google Play license key, and so on.
Icons: In this section, you can set your game's icons. You can set various sizes of icons depending upon the screen density of the device you are aiming to develop on. You can get more information about icons by click on the hyperlink at the top of the section.
Data Cooker: Finally, in this section, you can set how you want the audio in the game to be encoded.
For our game, the first thing you need to set is the Android Package Name which is found in the APKPackaging section. The format of the naming is com.YourCompany.[PROJECT]. Here, replace YourCompany with the name of the company and [PROJECT] with the name of your project.
Building a package
To package your project, in the Editor go to File | Package Project | Android.
You will see different types of formats to package the project in. These are as follows:
ATC: Use this format if you have a device that has a Qualcomm Snapdragon processor.
DXT: Use this format if your device has a Tegra graphical processing unit (GPU).
ETC1: You can use this for any device. However, this format does not accept textures with alpha channels. Those textures will be uncompressed, making your game requiring more space.
ETC2: Use this format is you have a MALI-based device.
PVRTC: Use this format if you have a device with a PowerVR GPU.
Once you have decided upon which format to use, click on it to begin the packaging process. A window will open up asking you to specify which folder you want the package to be stored in.
Once you have decided where to store the package file, click OK and the build process will commence. When started, just like with launching the project, a small window will pop up at the bottom-right corner of the screen notifying the user that the build process has begun. You can open the output log and cancel the build process.
Once the build process is complete, go the folder you set.
You will find a .bat file of the game. Providing you have checked the packaged game data inside .apk? option (which is located in the Project settings in the Android category under the APKPackaging section), you will also find an .apk file of the game.
The .bat file directly installs the game from the system onto your device. To do so, first connect your device to the system. Then double-click on the .bat file. This will open a command prompt window.
Once it has opened, you do not need to do anything. Just wait until the installation process finishes. Once the installation is done, the game will be on your device ready to be executed.
To use the .apk file, you will have to do things a bit differently. An .apk file installs the game when it is on the device. For that, you need to perform the following steps:
Connect the device.
Create a copy of the .apk file.
Paste it in the device's storage.
Execute the .apk file from the device.
The installation process will begin. Once completed, you can play the game.
Summary
In this article, we covered with Blueprints and discussed how they work. We also discussed Level Blueprints and the Blueprint class, and covered how to script AI. We discussed how to package the final product and upload the game onto the Google Play Store for people to download.
Resources for Article:
Further resources on this subject:
Flash Game Development: Creation of a Complete Tetris Game [article]
Adding Finesse to Your Game [article]
Saying Hello to Unity and Android [article]
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