Fix camera framing for large grids using corner projection

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

Source/Tactica/Private/TacticaCameraPawn.cpp

@@ -1,6 +1,8 @@
 #include "TacticaCameraPawn.h"
 #include "Camera/CameraComponent.h"
 #include "GridManager.h"
+#include "Engine/GameViewportClient.h"
+#include "Engine/World.h"
 #include "Kismet/GameplayStatics.h"
 
 DEFINE_LOG_CATEGORY_STATIC(LogTacticaCamera, Log, All);
@@ -25,12 +27,53 @@ void ATacticaCameraPawn::BeginPlay()
 		return;
 	}
 
-	// グリッドの長辺の半分(余白つき)が画角に収まる距離を求める
-	const float HalfExtent = FMath::Max(Grid->GridSizeX, Grid->GridSizeY) * Grid->CellSize * 0.5f * MarginScale;
-	const float HalfFovRad = FMath::DegreesToRadians(Camera->FieldOfView * 0.5f);
-	const float Distance = HalfExtent / FMath::Tan(HalfFovRad);
-
 	const FRotator Rotation(Pitch, 0.0f, 0.0f);
-	const FVector Location = Grid->GetGridCenter() - Rotation.Vector() * Distance;
-	SetActorLocationAndRotation(Location, Rotation);
+	const FVector Center = Grid->GetGridCenter();
+
+	// 画面の縦横比(取れなければカメラの既定値)
+	float Aspect = Camera->AspectRatio;
+	if (const UWorld* World = GetWorld())
+	{
+		if (const UGameViewportClient* Viewport = World->GetGameViewport())
+		{
+			FVector2D Size;
+			Viewport->GetViewportSize(Size);
+			if (Size.X > 1.0f && Size.Y > 1.0f)
+			{
+				Aspect = Size.X / Size.Y;
+			}
+		}
+	}
+
+	// 横方向・縦方向の画角の半分のtan(余白の分だけ狭めて使う)
+	const float TanH = FMath::Tan(FMath::DegreesToRadians(Camera->FieldOfView * 0.5f)) / MarginScale;
+	const float TanV = TanH / FMath::Max(Aspect, 0.1f);
+
+	// グリッドの四隅が画面に収まる最小の距離を求める。
+	// 斜めに見下ろすので、手前の辺は近く、奥の辺は遠い(深さが違う)ことを考慮する
+	const FRotationMatrix RotMatrix(Rotation);
+	const FVector ViewDir = RotMatrix.GetUnitAxis(EAxis::X);
+	const FVector Right = RotMatrix.GetUnitAxis(EAxis::Y);
+	const FVector Up = RotMatrix.GetUnitAxis(EAxis::Z);
+
+	const float HalfX = Grid->GridSizeX * Grid->CellSize * 0.5f;
+	const float HalfY = Grid->GridSizeY * Grid->CellSize * 0.5f;
+
+	float Distance = 0.0f;
+	for (int32 SignX = -1; SignX <= 1; SignX += 2)
+	{
+		for (int32 SignY = -1; SignY <= 1; SignY += 2)
+		{
+			const FVector Offset(SignX * HalfX, SignY * HalfY, 0.0f);
+			const float Depth = FVector::DotProduct(Offset, ViewDir);  // 中心からの奥行きのずれ
+			const float Lateral = FMath::Abs(FVector::DotProduct(Offset, Right));
+			const float Vertical = FMath::Abs(FVector::DotProduct(Offset, Up));
+
+			// 条件: Lateral <= (Distance + Depth) * TanH, Vertical <= (Distance + Depth) * TanV
+			Distance = FMath::Max(Distance, Lateral / TanH - Depth);
+			Distance = FMath::Max(Distance, Vertical / TanV - Depth);
+		}
+	}
+
+	SetActorLocationAndRotation(Center - ViewDir * Distance, Rotation);
 }