UE4中提供了很多預定義的調試繪製函數，在做調試的時候還是比較方便的。可以在場景裏繪製點、線、圓、球、箭頭、椎體、膠囊、甚至樣條線、字符串、網格等等，基本上該有的都有了。比較讚的是，你能控制線條的厚度，調試的時候就比較直觀了。
要使用這些函數，只需要包含DrawDebugHelpers.h 頭文件即可。下面介紹幾個主要的繪製函數：
1.繪製點
ENGINE_API void DrawDebugPoint(const UWorld* InWorld, FVector const& Position, float Size, FColor const& PointColor, bool bPersistentLines = false, float LifeTime=-1.f, uint8 DepthPriority = 0);可選參數裏面，我們可以控制點的尺寸、顏色、持續時間等。bPersistentLines表示，當前繪製的整個對象，是不是持久對象，設爲true，它會一直顯示當前World，直到你調用下面這個方法，釋放它：
void FlushPersistentDebugLines(const UWorld* InWorld);2.繪製線
ENGINE_API void DrawDebugLine(const UWorld* InWorld, FVector const& LineStart, FVector const& LineEnd, FColor const& Color, bool bPersistentLines = false, float LifeTime=-1.f, uint8 DepthPriority = 0, float Thickness = 0.f);注意Thickness這個參數，它控制線條的厚度。
3.繪製箭頭
ENGINE_API void DrawDebugDirectionalArrow(const UWorld* InWorld, FVector const& LineStart, FVector const& LineEnd, float ArrowSize, FColor const& Color, bool bPersistentLines = false, float LifeTime=-1.f, uint8 DepthPriority = 0);4.繪製Box
ENGINE_API void DrawDebugBox(const UWorld* InWorld, FVector const& Center, FVector const& Extent, FColor const& Color, bool bPersistentLines = false, float LifeTime=-1.f, uint8 DepthPriority = 0);
/** Draw a debug box with rotation */
ENGINE_API void DrawDebugBox(const UWorld* InWorld, FVector const& Center, FVector const& Box, const FQuat & Rotation, FColor const& Color, bool bPersistentLines = false, float LifeTime=-1.f, uint8 DepthPriority = 0);第一個根據Box的尺寸繪製，第二個額外的可以按照一定的旋轉繪製。
5.繪製球體
ENGINE_API void DrawDebugSphere(const UWorld* InWorld, FVector const& Center, float Radius, int32 Segments, FColor const& Color, bool bPersistentLines = false, float LifeTime=-1.f, uint8 DepthPriority = 0);
6.其他
還有很多不太常用的，可以繪製2D圓、圓柱、椎體、平截頭體、膠囊等。這裏只列出來，具體見DrawDebugHelpers.h
ENGINE_API void DrawDebugCoordinateSystem(const UWorld* InWorld, FVector const& AxisLoc, FRotator const& AxisRot, float Scale, bool bPersistentLines = false, float LifeTime=-1.f, uint8 DepthPriority = 0);
/** Draw Debug Circle */
ENGINE_API void DrawDebugCircle(const UWorld* InWorld, const FMatrix& TransformMatrix, float Radius, int32 Segments, const FColor& Color, bool bPersistentLines = false, float LifeTime=-1.f, uint8 DepthPriority = 0);
/** Draw Debug 2D donut */
ENGINE_API void DrawDebug2DDonut(const UWorld* InWorld, const FMatrix& TransformMatrix, float InnerRadius, float OuterRadius, int32 Segments, const FColor& Color, bool bPersistentLines = false, float LifeTime=-1.f, uint8 DepthPriority = 0);
/** Draw a debug sphere */
ENGINE_API void DrawDebugSphere(const UWorld* InWorld, FVector const& Center, float Radius, int32 Segments, FColor const& Color, bool bPersistentLines = false, float LifeTime=-1.f, uint8 DepthPriority = 0);
/** Draw a debug cylinder */
ENGINE_API void DrawDebugCylinder(const UWorld* InWorld, FVector const& Start, FVector const& End, float Radius, int32 Segments, FColor const& Color, bool bPersistentLines = false, float LifeTime=-1.f, uint8 DepthPriority = 0);
ENGINE_API void DrawDebugCone(const UWorld* InWorld, FVector const& Origin, FVector const& Direction, float Length, float AngleWidth, float AngleHeight, int32 NumSides, FColor const& Color, bool bPersistentLines=false, float LifeTime=-1.f, uint8 DepthPriority = 0);
/** Used by gameplay when defining a cone by a vertical and horizontal dot products. */
ENGINE_API void DrawDebugAltCone(const UWorld* InWorld, FVector const& Origin, FRotator const& Rotation, float Length, float AngleWidth, float AngleHeight, FColor const& DrawColor, bool bPersistentLines=false, float LifeTime=-1.f, uint8 DepthPriority=0);
ENGINE_API void DrawDebugString(const UWorld* InWorld, FVector const& TextLocation, const FString& Text, class AActor* TestBaseActor = NULL, FColor const& TextColor = FColor::White, float Duration = -1.000000);
ENGINE_API void DrawDebugFrustum(const UWorld* InWorld, const FMatrix& FrustumToWorld, FColor const& Color, bool bPersistentLines = false, float LifeTime=-1.f, uint8 DepthPriority = 0);
/** Draw a capsule using the LineBatcher */
ENGINE_API void DrawDebugCapsule(const UWorld* InWorld, FVector const& Center, float HalfHeight, float Radius, const FQuat & Rotation, FColor const& Color, bool bPersistentLines=false, float LifeTime=-1.f, uint8 DepthPriority = 0);
/** Draw a debug camera shape. FOV is full angle in degrees. */
ENGINE_API void DrawDebugCamera(const UWorld* InWorld, FVector const& Location, FRotator const& Rotation, float FOVDeg, float Scale=1.f, FColor const& Color=FColor::White, bool bPersistentLines=false, float LifeTime=-1.f, uint8 DepthPriority = 0);
ENGINE_API void FlushDebugStrings(const UWorld* InWorld);
ENGINE_API void DrawDebugSolidBox(const UWorld* InWorld, FVector const& Center, FVector const& Box, FColor const& Color, bool bPersistent=false, float LifeTime=-1.f, uint8 DepthPriority = 0);
ENGINE_API void DrawDebugSolidBox(const UWorld* InWorld, FVector const& Center, FVector const& Extent, FQuat const& Rotation, FColor const& Color, bool bPersistent=false, float LifeTime=-1.f, uint8 DepthPriority = 0);
ENGINE_API void DrawDebugMesh(const UWorld* InWorld, TArray<FVector> const& Verts, TArray<int32> const& Indices, FColor const& Color, bool bPersistent=false, float LifeTime=-1.f, uint8 DepthPriority = 0);
ENGINE_API void DrawDebugSolidPlane(const UWorld* InWorld, FPlane const& P, FVector const& Loc, float Size, FColor const& Color, bool bPersistent=false, float LifeTime=-1, uint8 DepthPriority = 0);
/* Draws a 2D Histogram of size 'DrawSize' based FDebugFloatHistory struct, using DrawTransform for the position in the world. */
ENGINE_API void DrawDebugFloatHistory(UWorld const & WorldRef, FDebugFloatHistory const & FloatHistory, FTransform const & DrawTransform, FVector2D const & DrawSize, FColor const & DrawColor, bool const & bPersistent = false, float const & LifeTime = -1.f, uint8 const & DepthPriority = 0);
/* Draws a 2D Histogram of size 'DrawSize' based FDebugFloatHistory struct, using DrawLocation for the location in the world, rotation will face camera of first player. */
ENGINE_API void DrawDebugFloatHistory(UWorld const & WorldRef, FDebugFloatHistory const & FloatHistory, FVector const & DrawLocation, FVector2D const & DrawSize, FColor const & DrawColor, bool const & bPersistent = false, float const & LifeTime = -1.f, uint8 const & DepthPriority = 0);
