Have you ever thought about procedurally generated levels? Have you thought about how this could be done, how their logic works, and how their resources are managed?
With our example bricks game, you will get to the core point of generating colors procedurally for each block, every time the level gets loaded.
Physics has always been a huge and massively important topic in the process of developing a game. However, a brick breaking game can be made in many ways and using the many techniques that the engine can provide, but I choose to make it a physics-based game to cover the usage of the new, unique, and amazing component that Epic has recently added to its engine.
The Projectile component is a physics-based component for which you can tweak many attributes to get a huge variation of behaviors that you can use with any game genre.
By the end of this article by Muhammad A.Moniem, the author of Learning Unreal Engine iOS Game Development, you will be able to:
Build your first multicomponent blueprints
Understand more about the game modes
Script a touch input
Understand the Projectile component in depth
Build a simple emissive material
Use the dynamic material instances
Start using the construction scripts
Detect collisions
Start adding sound effects to the game
Restart a level
Have a fully functional gameplay
(For more resources related to this topic, see here.)
The project structure
For this game sample, I made a blank project template and selected to use the starter content so that I could get some cubes, spheres, and all other 3D basic meshes that will be used in the game. So, you will find the project structure still in the same basic structure, and the most important folder where you will find all the content is called Blueprints.
Building the blueprints
The game, as you might see in the project files, contains only four blueprints. As I said earlier, a blueprint can be an object in your world or even a piece of logic without any physical representation inside the game view. The four blueprints responsible for the game are explained here:
ball: This is the blueprint that is responsible for the ball rendering and movement. You can consider it as an entity in the game world, as it has its own representation, which is a 3D ball.
platform: This one also has its visual representation in the game world. This is the platform that will receive the player input.
levelLayout: This one represents the level itself and its layout, walls, blocks, and game camera.
bricksBreakingMode: Every game or level made with Unreal Engine should have a game mode blueprint type. This defines the main player, the controller used to control the gameplay, the pawn that works in the same way as the main player but has no input, the HUD for the main UI controller, and the game state that is useful in multiplayer games. Even if you are using the default setting, it will be better to make a space holder one!
Gameplay mechanics
I've always been a big fan of planning the code before writing or scripting it. So, I'll try to keep the same habit here as well; before making each game, I'll explain how the gameplay workflow should be. With such a habit, you can figure out the weak points of your logic, even if you didn't build it. It helps you develop quickly and more efficiently.
As I mentioned earlier, the game has only three working blueprints, and the fourth one is used to organize the level (which is not gameplay logic and has no logic at all). Here are the steps that the game should follow one by one:
At the start of the game, the levelLayout blueprint will start instantiating the bricks and set a different color for each one.
The levelLayut blueprint sets the rendering camera to the one we want.
The ball blueprint starts moving the ball with a proper velocity and sets a dynamic material for the ball mesh.
The platform blueprint starts accepting the input events on a frame-by-frame basis from mouse or touch inputs, and sets a dynamic material for the platform mesh.
If the ball blueprint hits any other object, it should never speed up or slow down; it should keep the same speed.
If the ball blueprint crossed the bottom line, it should restart the level.
If the player pressed the screen or clicked on the mouse, the platform blueprint should move only on the y axis to follow the finger or the mouse cursor.
If the ball blueprint hits any brick from the levelLayout blueprint, it should destroy it.
The ball plays some sound effects. Depending on the surface it hits, it plays a different sound.
Starting a new level
As the game will be based on one level only and the engine already gives us this new pretty level with a sky dome and light effects with some basic assets, all of this will not be necessary for our game. So, you need to go to the File menu, select New Level, add it somewhere inside your project files, and give it a special name. In my case, I made a new folder named gameScene to hold my level (or any other levels if my game is a multilevel game) and named it mainLevel.
Now, this level will never get loaded into the game without forcing the engine to do that. The Unreal Editor gives you a great set of options to define which is the default map/level to be loaded when the game starts or when the editor runs. Even when you ship the game, the Unreal Editor tells us which levels should be shipped and which levels shouldn't be shipped to save some space.
Open the Edit menu and then open Project Settings. When the window pops up, select the Maps & Modes section and set Game Default Map to the newly created level. Editor Startup Map should also have the same level:
Building the game mode
Although a game mode is a blueprint, I prefer to always separate its creation from the creation of the game blueprints, as it contains zero work for logic or even graphs. A game mode is essential for each level, not only for each game.
Right-click in an empty space inside your project directory and select Blueprint under the Basic assets section. When the Pick Parent Class window pops up, select the last type of blueprint, which is called Game Mode, and give your newly created blueprint a name, which, in my case, is bricksBreakingMode.
Now, we have a game mode for the game level; this mode will not work at all without being connected to the current level (the empty level I made in the previous section) somehow.
Go to World Settings by clicking on the icon in the top shelf of the editor (you need to get used to accessing World Settings, as it has so many options that you will need to tweak them to fit your games):
The World Settings panel will be on the right-hand side of your screen. Scroll down to the Game Mode part and select the one you made from the Game Mode Override drop-down menu.
If you cannot find the one you've made, just type its name, and the smart menu will search over the project to find it.
Building the game's main material
As the game is an iOS game, we should work with caution when adding elements and code to save the game from any performance overhead, glitches, or crashes. Although the engine can run a game with the Light option on an iOS device, I always prefer to stay as far away as possible from using lights/directional lights in an iOS game, as a directional light source on mealtime would mean recalculating all the vertices. So, if the level has 10k vertices with two directional lights, it will be calculated as 30k vertices.
The best way to avoid using a light source for such a simple game like the brick breaking game is to build a special material that can emulate a light emission; this material is called an emissive material.
In your project panel, right-click in an empty space (perhaps inside the materialsfolder) and choose a material from the Basic Assets section. Give this material a name (which, in my case, is gameEmissiveMaterial) and then double-click to open the material editor.
As you can see, the material editor for a default new material is almost empty, apart from one big node that contains the material outputs with a black colored material. To start adding new nodes, you will need to right-click in an empty space of your editor grid and then either select a node or search for nodes by name; both ways work fine.
The emissive material is just a material with Color and Emissive Color; you can see these names in your output list, which means you will need to connect some sort of nodes or graphs to these two sockets of the material output.
Now, add the following three new nodes:
VectorParameter: This represents the color; you can pick a color by clicking on the color area on the left-hand panel of the screen or on the Default Value parameter.
ScalarParameter: This represents a factor to scale the color of the material; you can set its Default Value to 2, which works fine for the game.
Multiply: This will multiply two values (the color and the scalar) to give a value to be used for the emission.
With these three nodes in your graph, you might figure out how it works. The basic color has to be added to the base color output, and then the Multiply result of the base color and scalar will be added to the emissive color output of the material:
You can rename the nodes and give them special names, which will be useful later on. I named the VectorParameter node BaseColor and the Scalar node EmissiveScalar.
You can check out the difference between the emissive material you made and another default material by applying both to two meshes in a level without any light. The default material will light the mesh in black as it expects a light source, but the emissive one will make it colored and shiny.
Building the blueprints and components
I prefer to call all the blueprints for this game actors as all of them will be based on a class in the engine core. This class usually represents any object with or without logic in the level. Although blueprints based on the actor class are not accepting input, you will learn a way to force any actor blueprint to get input events. In this section, you will build the different blueprints for the game and add components for each one of them. Later on, in another section, you will build the logic and graphs. As I always say, building and setting all the components and the default values should be the first thing you do in any game, and then adding the logic should follow. Do not work on both simultaneously!
Building the layout blueprint
The layout blueprint should include the bricks that the players are going to break, the camera that renders the level, and the walls that the ball is going to collide with.
Start making it by adding an Actor blueprint in your project directory. Name it levelLayout and double-click on it to open the blueprint editor.
The blueprint editor, by default, contains the following three subeditors inside it; you can navigate between them via the buttons in the top-right corner:
Defaults: This is used to set the default values of the blueprint class type
Components: This is used to add different components to build and structure the blueprint
Graph: This is where we will add scripting logic
The majority of the time, you will be working with the components and graph editors only, as the default editor's default values always work the best:
Open the component graph and start adding these components:
Camera: This will be the component that renders the game. As you can see in the preceding screenshot, I added one component and left its name as Camera1. It was set as ROOT of the blueprint; it holds all the other components as children underneath its hierarchy.
Changed Values: The only value you need to change in the camera component is Projection Mode. You need to set it to Orthographic, as it will be rendered as a 2D game, and keep Ortho Width as 512, as it will make the screen show all the content in a good size. Feel free to use different values based on the content of your level design.
Orthographic cameras work without depth, and they are recommended more in 2D games. On the other hand, the perspective camera has more depth, and it is better to be used with any games with 3D content.
Static Mesh: To be able to add meshes as boundaries or triggering areas to collide with the ball, you will need to add cubes to work as collision walls, perhaps hidden walls. The best way to add this is by adding four static meshes and aligning and moving them to build them as a scene stage. Renaming all of them is also a good way to go. To be able to distinguish between them, you can name them as I named them: StaticMeshLeftMargin, StaticMeshRightMargin, StaticMeshTopMargin, and StaticMeshBottomMargin. The first three are the left, right, and top margins; they will be working as collision walls to force the ball to bounce in different directions. However, the bottom one will work as a trigger area to restart the level when the ball passes through it.
Changed Values: You need to set Static Mesh for them as the cube and then start to scale and move it to build the scene.
For the walls, you need to add the Wall tag for the first three meshes in the Component Tags options area, and for the bottom trigger, you need to add another tag; something like deathTrigger works fine. These tags will be used by the gameplay logic to detect whether the ball hits a wall and you need to play a sound or whether it hits a death area and you need to restart the level.
In the Collision section for each static mesh, you need to set both SimulationGeneratesHitEvents and GenerateOverlapEvents to True. Also, for CollisionPreset, you can select BlockAll, as this will create solid walls to block any other object from passing:
Finally, from the Rendering options section, you need to select the emissive material we have made to be able to see those static meshes, and you need to mark Hidden in Game as True to hide those objects. Keep in mind that you can keep those objects in the game for debugging reasons, and when you are sure that they are in the correct place, you can move to this option again and remark it as True.
Billboard: For now, you can think about the billboard component as a point in space with a representation icon, and this is how it is mostly used inside UE4 as the engine does not support an independent transform component yet. However, billboards have always been used to show the contents that always face the camera, such as particles, text, or any other thing you need to always get rendered from the same angle. As the game will be generating the blocks/bricks during the gameplay, you will need to have some points to define where to build or to start building those bricks. You can add five billboard points, rename them, and rearrange them to look like a column. You don't have to change any values for them, as you will be using their position in space values only! I named those five points as firstRowPoint, SecondRowPoint, thirdRowPoint, fourthRowPoint, and fifthRowPoint.
Building the ball blueprint
Start making the ball blueprint by adding an Actor blueprint in your project directory. Name it Ball and double-click on it to open the blueprint editor. Then, navigate to the Components subeditor if you are not ready. Start adding the following components to the blueprint:
The sphere will work as the collision surface for the Ball blueprint. So, for this reason, you will need to set its Collision option to SimulationGeneratesHitEvents and GenerateOverlapEvents to True. Also, set the CollisionPreset option to BlockAll to act in a manner similar to the walls from the layout blueprint. You need to set the SphereRadius option from the Shape section to 26.0 so that it is of a good size that fits the screen's overall size.
The process for adding static meshes is the same as you did earlier, but this time, you will need to select a sphere mesh from the standard assets that came with the project. You will also need to set its material to the project default material you made earlier in this article. Also, after selecting it, you might need to adjust its Scale to 0.5 in all three axes to fit the collision sphere size. Feel free to move the static mesh component on the x, y, and z axes till it fits the collision surface.
The projectile movement component is the most important one for the Ball blueprint, or perhaps it is the most important one throughout this article, as it is the one responsible for the ball movement and velocity and for its physics behaviors. After adding the components, you will need to make some tweaks to it to allow it to give the behavior that matches the game. Keep in mind that any small amount of change in values or variables will lead you to have a completely different behavior, so feel free to play through the values and test them to get some crazy ideas about what you can achieve and what you can get.
For changed values, you need to set Projectile Gravity Scale to 0.0 from within the Projectile options; this will allow the ball to fly in the air without a gravity force to bring it down (or any other direction for a custom gravity).
For Projectile Bounces, you will need to mark Should Bounce as True. In this case, the projectile physics will be forced to keep bouncing with the amount of bounciness you set. As you want the ball to keep bouncing over the walls, you need to set the value to 1.0 to give it full bounciness power:
From the Velocity section, you will need to enter a velocity for the ball to start using when the game runs; otherwise, the ball will never move. As you want the first bounce of the ball to be towards the blocks, you need to set the Z value to a high number, such as 300, and give it more level design sense. It shouldn't bounce in a vertical line, so it is better to give some force on the horizontal axis Y as well as move the ball in a diagonal direction. So, let's add 300 into Y as well.
Building the platform blueprint
Start making the platform blueprint by adding an Actor blueprint in your project directory. Name it platform and double-click on it to open the blueprint editor. Then, navigate to the Components subeditor if you are not there already. You will add only one component, and it will work for everything. You want to add a Static Mesh component, but this time, you will be selecting the Pipe mesh; you can select whatever you want, but the pipe works the best.
Don't forget to set its material to be the same emissive material as we used earlier to be able to see it in the game view, and set its Collision option to SimulationGeneratesHitEvents and GenerateOverlapEvents to True. Also, CollisionPreset should be set to BlockAll to act in the same manner as the walls from the layout blueprint.
Building the graphs and logic
Now, as all the blueprints have been set up with their components, it's time to start adding the gameplay logic/scripting. However, to be able to see the result of what you are going to build, you first need to drag and drop the three blueprints inside your scene and organize them to look like an actual level.
As the engine is a 3D engine and there is no support yet for 2D physics, you might notice that I added two extra objects to the scene (giant cubes), which I named depthPreservingCube and depthPreservingCube2. These objects are here basically to prevent the ball from moving in the depth axis, which is X in Unreal Editor. This is how both the new preserving cubes look from a top view:
One general step that you will perform for all blueprints is to set the dynamic material for them. As you know, you made only one material and applied it to the platform and to the ball. However, you also want both to look different during the gameplay. Changing the material color right now will change both objects' visibility. However, changing it during the gameplay via the construction script and the dynamic material instances feature will allow you to have many colors for many different objects, but they will still share the same material.
So, in this step, you will make the platform blueprint and the ball blueprint. I'll explain how to make it for the ball, and you will perform the same steps to make it for the platform. Select the ball blueprint first and double-click to open the editor; then, this time navigate to the subeditor graphs to start working with the nodes.
You will see that there are two major tabs inside the graph; one of them is named Construction Script. This unique tab is responsible for the construction of the blueprint itself. Open the Construction Script tab that always has a Construction Script node by default; then, drag and drop the StaticMesh component of the ball from the panel on the left-hand side. This will cause you to have a small context menu that has only two options: Get and Set. Select Get, and this will add a reference to the static mesh.
Now, drag a line from Construction Script, leave it in an empty space, add a Create Dynamic Material Instance node from the context menu, and set its Source Material option to the material we want to instance (which is the emissive material). However, keep in mind that if you are using a later version, Epic introduces a more easy way to access the Create Dynamic Material Instance node by just dragging a line from Static Mesh-ball inside Graph, and not Construction Script.
Now, connect the static mesh to be the target and drag a line out of Return Value of the Create Dynamic Material Instance node. From the context menu, select the first option, which is Promote to a Variable; this will add a variable to the left-panel list. Feel free to give it a name you can recognize, which, in my case, is thisColor. Now, the whole thing should look like this:
Now that you've created the dynamic material instance, you need to set the new color for it. To do this, you need to go back to the event graph and start adding the logic for it. I'll add it to the ball also, and you need to apply it again in Event Graph of the platform blueprint.
Add an Event Begin Play node, which is responsible for the execution of some procedurals when the game starts. Drag a wire out of it and select the Set Vector Parameter Value node that is responsible for setting the value for the material.
Now, add a reference for the thisColor variable and connect it to Target of the Set Vector Parameter Value node. Last but not least, enter Parameter name that you used to build the material, which, in my case, is BaseColor.
Finally, set Value to a color you like; I picked yellow for the ball. Which color would you like to pick?
The layout blueprint graph
Before you start working with this section, you need to make several copies of the material we made earlier and give each one its own color. I made six different ones to give a variation of six colors to the blocks.
The scripts here will be responsible for creating the blocks, changing their colors, and finally, setting the game view to the current camera. To serve this goal, you need to add several variables with several types. Here are some variables:
numberOfColumns: This is an integer variable that has a default value of six, which is the total number of columns per row.
currentProgressBlockPosition: This is a vector type variable to hold the position of the last created block. It is very important because you are going to add blocks one after the other, so you want to define the position of the last block and then add spacing to it.
aBlockMaterial: This is the material that will be applied to a specific block.
materialRandomIndex: This is a random integer value to be used for procedural selected colors for each block.
To make things more organized, I managed to make several custom events. You can think about them as a set of functions; each one has a block of procedurals to execute:
Initialize The Blocks: This Custom Event node has a set of for loops that are working one by one on initializing the target blocks when the game starts. Each loop cycles six times from Index 0 to the number of columns index. When it is finished, it runs the next loop. Each loop body is a custom function itself, and they all run the same set of procedurals, except that they use a different row.
chooseRandomMaterial: This custom event handles the process of picking a random material to be applied to in the process of creation. It works by setting a random value between 1 and 6 to the materialRandomIndex variable, and depending on the selected value, the aBlockMaterial variable will be set to a different material. This aBlockMaterial variable is the one that will be used to set the material of each created block in each iteration of the loop for each row.
addRowX: I named this X here, but in fact, there are five functions to add the rows; they are addRow1, addRow2, addRow3, addRow4, and addRow5. All of them are responsible for adding rows; the main difference is the start point of adding the row; each one of them uses a different billboard transform, starting from firstRowPoint and ending with fifthRowPoint. You need to connect your first node as Add Static Mesh and set its properties as any other static mesh. You need to set its material to the emissive one. Set Static Mesh to Shape_Pipe_180, give it a brickPiece tag, and set its Collision options to Simulation Generates Hit Events and Generate Overlap Events to True. Also, Collision Preset has to be set to Block All to act in the same manner as the walls from the layout blueprint and receive the hit events, which will be the core of the ball detection. This created mesh will need a transform point to be instantiated in its cords. This is where you will need to pick the row point transform reference (depending on your row, you will select the point number), add it to a Make Transform node, and finally, set the new transform Y Rotation to -90 and its XYZ scale to 0.7, 0.7, 0.5 to fit the correct size and flip the block to have a better convex look.
This second part of the addRow event should use the ChooseRandomMaterial custom event that you already made to select a material from among six random ones. Then, you can execute SetMaterial, make its Target the same mesh that was created via Add Static Mesh, and set its Material to aBlockMaterial; the material changes every time the chooseRandomMaterial event gets called.
Finally, you can use SetRelativeLocation of the billboard point that is responsible for that row to another position on the y axis, using the Make Vector and Add Int(+) nodes to add 75 units every time as a spacing between every two created blocks:
Now, if you check the project files, you will find that the only difference is that there are five functions called addRow, and each of them uses a different billboard as a starting point to add the blocks. Now, if you run the version you made or the one within the project files, you will be able to see the generated blocks, and each time you stop and run the game, you will get a completely different color variation of the blocks.
There is one last thing to completely finish this blueprint. As you might have noticed, this blueprint contains the camera in its components. This means it should be the one that holds the functionality of setting this camera to be the rendering camera. So, in EvenBeginPlay, this functionality will be fired when the level starts. You need to connect the the Set View Target With Blend node that will set the camera to the Target camera, and you need to connect Get Player Controller (player 0 is the player number 1) to the Target socket. This blueprint refers to New View Target. Finally, you need to call the initializeTheBlocks custom event, which will call all the other functions.
Congratulations! Now you have built your first functional and complex blueprint that contains the main and important functionalities everyone must use in any game. Also, you got the trick of how you can randomly generate or change things such as the color of the blocks to make the levels feel different every time.
The Ball blueprint graph
The main event node that will be used in the ball graph is Event Hit, which will be fired automatically every time the ball collider hits another collider. If you still remember, while creating the platform, walls, and blocks, we used to add tags for every static mesh to define them. Those names are used now. Using a node called Component Has Tag, we can compare the object component that the ball has hit with the value of the Component Has Tag node, and then, we either get a positive or negative result. So, this is how it should work:
Whenever the ball gets hit with another collider, check whether it is a brickPiece tagged component. If this is true, then disable the collision of the brick piece via the Set Collision Enabled node and set it to No Collision to stop responding to any other collisions. Then, hide the brick mesh using the Set Visibility node and keep the New Visibility option unmarked, which means that it will be hidden. Then, play a sound effect of the hit to make it a more dynamic gameplay. You can play sound in many different ways, but let's use the Play Sound at Location node now, use the location of the ball itself, and use the hitBrick sound effect from the Audio folder by assigning it to the Sound slot of the Play Sound at Location node. Finally, reset the velocity of the ball using the Set Velocity node referenced by the Projectile Movement component and set it to XYZ 300, 0, 300:
If it wasn't a brickPiece tag, then let's check whether it is Component Has Tag of Wall. If this is the case, then let's use Play Sound at Location, use the location of the ball itself, and use the hitBlockingWall sound effect from the Audio folder by assigning it to the Sound slot of the Play Sound at Location node:
If it wasn't tagged with Wall, then check whether it is finally tagged with deathTrigger. If this is the case, then the player has missed it, and the ball is not below the platform. So, you can use the Open Level node to load the level again and assign the level name as mainLevel (or any other level you want to load) to the Level Name slot:
The platform blueprint graph
The platform blueprint will be the one that receives the input from the player. You just need to define the player input to make the blueprint able to receive those events from the mouse, touch, or any other available input device. To do this, there are two ways, and I always like to use both these ways:
Enable input node: I assume that you've already added the scripting nodes inside Event graph to set the dynamic material color via Set Vector Parameter Value. This means you already have an Event Begin Play node, so you need to connect its network to another node called Enable Input; this node is responsible for forcing the current blueprint to accept input events. Finally, you can set its Player Controller value to a Get Player Controller node and leave Player Index as 0 for the player number 1:
Autoreceive input option: By selecting the platform blueprint instance that you've dropped inside the scene from the Scene Outliner, you will see that it has many options in the Details panel on the right-hand side. By changing the Auto Receive Input option to Player 0 under the Input option, this will have the same effect as the previous solution:
Now, we can build the logic for the platform movement, and anything that is built can be tested directly in the editor or on the device. I prefer to break the logic into two pieces, and this will make it easier than it looks like for you:
Get the touch state: In this phase, you will use the Input Touch event that can be executed when a touch gets pressed or released. So based on the touch state, you will check via a Branch node whether the state is True or False. Your condition for this node should be Touch 1 index, as the game will not need more than one touch. Based on the state, I would like to set a custom Boolean variable named Touched and set its value to match the touch state. Then, you can add a Gate node to control the execution of the following procedurals based on the touch state (Pressed or Released) by connecting the two cases with the Open gate and the Close gate execution sockets. Finally, you can set the actor location and set it to use the Self actor as its target (which is the platform actor/blueprint) to change the platform location based on touches. Defining the New Location value is the next chunk of the logic:
Actor location: Using a Make Vector node, you can construct a new point position in the world made of X, Y, and Z coordinates. As the y axis will be the horizontal position, which will be based on the player's touch, only this needs to be changed over time. However, the X and Z positions will stay the same all the time, as the platform will never move vertically or in depth. The new vector position will be based on the touch phase. If the player is pressing, then the position should be matching the touch input position. However, if the players are not pressing, then the position should be the same as the last point the player had pressed. I managed to make a float variable named horizontalAxis; this variable will hold the correct Y position to be added to the Make Vector node. If the player is pressing the screen, then you need to get the finger press position by returning Impact Point by Break Hit Result via a Get Hit Result Under FingerBy Channel node from the current active player. However, if the player is not touching the screen, then the horizontalAxis variable should stay the same as the last-know location for the Self actor. Then, it will set as it is into the MakeVector Y position value:
Now, you can save and build all the blueprints. Don't hesitate now or any time during the process of building the game logic to build or launch the game into a real device to check where you are.
The best way to learn more about the nodes and those minor changes is by building all the time into the divide and changing some values every time.
Summary
In this article, you went through the process of building your first Unreal iOS game. Also, you got used to making blueprints by adding nodes in different ways, connecting nodes, and adding several component types into the blueprint and changing its values.
Also, you learned how to enable input in an actor blueprint and get the touch and mouse input and fit them to your custom use.
You also got your hands on one of the most famous and powerful rendering techniques in the editor, which is called dynamic material instancing. You learned how to make a custom material and change its parameters whenever you want.
Procedurally, changing the look of the level is something interesting nowadays, and we barely scratched its surface by setting different materials every time we load the level.
Resources for Article:
Further resources on this subject:
UnrealScript Game Programming Cookbook [article]
Unreal Development Toolkit: Level Design HQ [article]
The Unreal Engine [article]
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