Exploring UE5 Basics: Space Invaders
Eleazar Dz. Do.
Eleazar Dz. Do.
We start from the base game implementation: https://github.com/iestevez/spaceinvaders_ue5
We added some changes to the internal code, removing some boilerplate code, or simplifying other parts.
InvaderMovementComponent move its owner Actor(AInvader) only taking into account the commands given from the AInvaderSquad. Once is set to free through the variable bJumpFree, it will stop reacting to those commands. In the derived Blueprint BP_Invader we have added the new logic to do once has reached this state.
The logic set before was to create a set of points, that would make a circle path. And the invader will follow those keeping the order that were created. This was removed due to the use of splines to define new paths. Those paths could be configured in the editor for each new kind of invader.
After the invader has gone through the spline, it will take the direction of the player, but facing forward to axis X.
If the invader fails to kill the player, it will respawn at the top of the screen using the ReenterVolume.
InvaderSquad controls the entire squad of invaders, just like before, but we have change spawn logic making use of LocationVolume set in the editor. This allows us to set a space where we want to place the invaders, with some separation, and it will arrange them in a grid.
void AInvaderSquad::BuildSquad()
{
// Clean a possible squad
// ... omitted
// Spawn Invaders
FBoxSphereBounds SpawnableBounds = LocationVolume->GetBounds();
// Due to the Invader scale is tweaked the bounding box are way bigger than what it should be
auto InvaderScale = InvaderTemplate->Mesh->GetComponentScale();
auto InvaderBounds = InvaderTemplate->Mesh->Bounds.BoxExtent * InvaderScale * 2;
//OGEngine->AddOnScreenDebugMessage(-1, 15.0f, FColor::Yellow, FString::Printf(TEXT("X %f Y %f "), InvaderBounds.Origin.X, InvaderBounds.Origin.Z));
auto Spacing_X = (InvaderBounds.X) + ExtraSeparation;
auto Spacing_Y = (InvaderBounds.Y) + ExtraSeparation;
auto min = SpawnableBounds.Origin - SpawnableBounds.BoxExtent;
auto max = SpawnableBounds.Origin + SpawnableBounds.BoxExtent;
auto centerX = Spacing_X / 2 * (FGenericPlatformMath::Fmod(FMath::Abs(max.X - min.X), Spacing_X) /
ExtraSeparation);
auto centerY = Spacing_Y / 2 * (FGenericPlatformMath::Fmod(FMath::Abs(max.Y - min.Y), Spacing_Y) /
Spacing_Y);
int32 InvadersCount = 0;
FVector SpawnLocation;
// Invader Forward is opposite to Player Forward (Yaw rotation)
FRotator SpawnRotation = FRotator(0.0f, 180.0f, 0.0f);
FActorSpawnParameters SpawnParameters;
AInvader* SpawnedInvader;
for (float i = min.X; i < max.X; i += Spacing_X)
{
for (float j = min.Y; j < max.Y; j += Spacing_Y)
{
SpawnLocation = FVector(centerX + i, centerY + j, SpawnableBounds.Origin.Z);
SpawnParameters.SpawnCollisionHandlingOverride = ESpawnActorCollisionHandlingMethod::AlwaysSpawn;
SpawnParameters.Template = InvaderTemplate;
SpawnedInvader = GetWorld()->SpawnActor<AInvader>(InvaderClass, SpawnLocation, SpawnRotation, SpawnParameters);
SpawnedInvader->SetPositionInSquad(InvadersCount);
// We could attach the invaders to the squad to move only one transform
// SpawnedInvader->AttachToActor(this, ... , "");
++InvadersCount;
SquadMembers.Add(SpawnedInvader);
}
}
NumberOfMembers = InvadersCount;
State = InvaderMovementType::RIGHT;
}This was set on first place into a OnConstruction method, but it crashes the editor when trying to compile the Invader blueprint. So, I recommend to not SpawnActors in the OnConstruction method, at least those that are create with BP.
To implement this we create a new GameInstance class, that will hold the information of the leaderboard. The information is represented in the UScoreData class, this allows to easily implement algorithms like sorting in c++ rather than a possible spaghetti blueprint.
To implement the leaderboard we create a new widget that can be accessed through the Main Menu.
This "tab" can be switched using the two events implemented in the BP_MenuHUD.
The score is represented with a list view, that we fill through the ScoreData in the GameInstance.
And for each entry we extract the data to feed the widgets.
Before, Game Hud require an individual setting of the icon visibility. So, each icon have the exact same logic just changing the index. This has been simplified into a loop which set the visibility of those icons in one go.
We added a new material to the background, with a parallax effect using stars and nebula clouds
And the effect:
We added a new Niagara System, that gets triggered when the invaders get destroyed. This is done through C++ code.
// Invader.cpp
UNiagaraFunctionLibrary::SpawnSystemAttached(NFXExplosion, RootComponent, NAME_None, FVector(0.f), FRotator(0.f), EAttachLocation::KeepRelativeOffset, true);
We simply increase the difficulty by increasing some spawn values.
// InvaderSquad.cpp
void AInvaderSquad::IncreaseLevel()
{
FreeJumpRate *= 0.9;
InvaderTemplate->FireRate = InvaderTemplate->FireRate * 0.9;
}So, to understand why lowering the FreeJumpRate would increase the difficulty, we need to look at the new formula used.
1-e^(-TimeFromLastShot * DeltaTime/ YourRate)
With this, we can define YourRate, as the time that takes to trigger. If we set it to 20s, it means that will take around 20s to trigger again.
// Invader.cpp
// ... omitted
float val = FMath::RandRange(0.0f, 1.0f);
if (val < 1.0 - FMath::Exp(-TimeFromLastShot * DeltaTime / FireRate))
{
Fire();
}
// ... omittedAnother difficulty added, it was to make reappear the invaders again, once they have gone through the bottom screen. This is done only for the case of free jump invaders.
// InvaderSquad.cpp
void AInvaderSquad::ReenterFromTop(AInvader* Invader)
{
FVector InvaderLocation = Invader->GetActorLocation();
// We could use a new random location inside that reenter volume
float XAxis = ReenterVolume->GetActorLocation().X;
Invader->SetActorLocation(FVector(XAxis, InvaderLocation.Y, InvaderLocation.Z));
}Some screenshots
