Thursday, January 22, 2015

Unreal Engine 4 Tutorial #3: Unit Selection Decals for RTS Games

Hi, welcome back for another UE4 Tutorial. This time, I'll be walking you through how to set up unit selection decals for RTS games. So the decals need to be visible, when a particular unit is selected, and set to hidden as soon as the unit is deselected. For this tutorial, I'm gonna start off from the Unreal Top Down Template.

First of all, I'll be changing the default controls a bit. Instead of using left mouse button to move the units, I'll be using right mouse button for character movement. I already have a decal texture, that I created in GIMP. If you don't have one, you could get my decal texture from the link below:

So once you have the texture ready, next step is to set up your decal material. For creating a decal material, we need to set the 'Material Domain' in the details panel to 'Deferred Decal'. I'm also setting the blend mode to 'Emissive' in my case. Then we multiply the texture with the required color and connect it to the 'Emissive' input for the material. I then connected the texture to the opacity as well, since I only want the white space of the original texture to be visible. Here's a screenshot of my material:

Now that we have the material ready, it's time to move on to the 'MyCharacter' blueprint to add the decal component to you character. In the components tab, go to 'Add Component' and add a decal component. In it's details panel, set the material to the decal material that we created earlier. Also set the 'Hidden in Game' attribute under the Rendering section to true. This way the decals will be hidden by default. We only want them to visible when the unit is selected. You'll probably need to adjust the transform settings to get it to display properly. For now, you can use the same settings that I'm using, as that will definitely work out of the box. 

Next stop - handling the show/hide selection decal based on character possession. So in the character blueprint's event graph, add the events 'Event Possessed' and 'Event Unpossessed'. Get the Selection Decal and set it hidden in game to true for event unpossessed and false for event possessed. It's fairly straight forward, but here's a screenshot anyways:

Now we're gonna handle the player input inside the player controller class. First, add an input button event for selecting units. Then we get the 'Hit Result under cursor for objects' and set it's object types to 'Pawn'. Then we break the Hit Result, get the Hit actor and cast it to my character class to see if it returns true. If it does, we have our player controller possess the character. So everytime the player clicks on a unit, the player controller will possess that unit, which will trigger the selection decal to become visible.

So with that, you should be having a working decal material for your character. But just so that we can try it out in an RTS scenario, I'm gonna add one more character to the level. In order to do that, just go to the Level Blueprint and use 'Spawn Actor from Class' at 'Event Begin Play' using the default character class. Just set some transform values and everything's set.

And here's a screenshot of my unit selection decal while running the game in the editor:

So that's it for now. Over the coming weekend, I'll try to make a basic Command UI tutorial for the Top Down Template using HUD Blueprints . Until then, goodbye.