UE4的资料还真是少啊，还是我自己来总结这些API吧，找起来也比较好找
在UE的源码当中，其中最主要的是 Plugins 文件夹里面的插件代码和 Source 文件夹里面的的引擎源代码
UE 引擎的Source文件夹里面的源代码分为五个部分，分别是 Developer （开发者）文件夹
Editor（编辑器）文件夹
Programs（程序）文件夹
Runtime（运行时）文件夹
ThirdParty（第三方）文件夹
一.Developer（开发者）
二.Editor（编辑器）
三.Programs（程序）
四.Runtime（运行时）
1.Advertising
2.AIModule
3.ALAudio
4.Analytics
5.Android
6.AnimationCore
7.AnimGraphRuntime
8.AppFramework
9.Apple
10.ApplicationCore
11.AssetRegistry
12.AudioAnalyzer
13.AudioCaptureCore
14.AudioCaptureImplementations
15.AudioExtensions
16.AudioMixer
17.AudioMixerCore
18.AudioPlatformConfiguration
19.AugmentedReality
20.AutomatinMessages
21.AutomationWorkder
22.AVEncoder
23.AVIWriter
24.BlueprintRuntime
25.BuildSettings
26.Cbor
27.CEF3Utils
28.CinematicCamera
29.ClientPilot
30.ClothingSystemRuntimeCommon
31.ClothingSystemRuntimeInterface
32.ClothingSystemRuntimeNv
33.CookedIterativeFile
34.Core
35.CoreUObject
36.CrashReportCore
37.CrunchCompression
38.D3D12RHI
39.Datasmith
40.DeveloperSettings
41.EmptyRHI
42.Engine
43.EngineMessages
44.EngineSettings
45.Experimental
46.ExternalRPCRegistry
47.EyeTracker
48.Foliage
49.FriendsAndChat
50.GameMenuBuilder
51.GameplayMediaEncoder
52.GameplayTags
53.GameplayTasks
54.HardwareSurvey
55.HeadMountedDisplay
56.IESFile
57.ImageCore
58.ImageWrapper
59.ImageWriteQueue
60.InputCore
61.InputDevice
62.InstallBundleManager
63.IOS
64.IPC
65.Json
66.JsonUtilities
67.Landscape
68.Launch
69.LevelSequence
70.Linux
71.LiveLinkInterface
72.LiveLinkMessageBusFramework
73.Lumin
74.Mac
75.MaterialShaderQualitySettings
76.Media
77.MediaAssets
78.MediaInfo
79.MediaUtils
80.MeshDescription
81.MeshUtilitiesCommon
82.Messaging
83.MessagingCommon
84.MessagingRpc
85.MoviePlayer
86.MovieScene
87.MovieSceneCapture
88.MovieSceneTracks
89.MRMsh
90.NavigationSystem
91.Navmesh
92.Net
93.NetworkFile
94.NetworkFileSystem
95.Networking
96.NetworkReplayStreaming
97.NonRealtimeAudioRenderer
98.NullDrv
99.NullInstallBundleManager
100.Online
101.OpenGLDrv
102.Overlay
103.PacketHandlers
104.PakFile
105.PerfCounters
106.PhysicsCore
107.PhysXCooking
108.Portal
109.PreLoadScreen
110.Projects
111.PropertyAccess
112.PropertyPath
113.RawMesh
114.RemoteImportMessaging
115.RenderCore
116.Renderer
117.RHI
118.RigVM
119.RSA
120.RuntimeAssetCache
121.SandboxFile
122.Serialization
123.SessionMessages
124.SessionServices
125.SignalProcessing
126.Slate
127.Slatecore
128.SlateNullRenderer
129.SlateRHIRenderer
130.Sockets
131.SoundFieldRendering
132.StaticMeshDescription
133.StreamingFile
134.StreamingPauseRendering
135,SynthBenchmark
136.TimeManagement
137.Toolbox
138.TraceLog
139.UE4Game
140.UMG
141.Unix
142.UnrealAudio
143.VectorVM
144.VirtualProduction
145.VulkanRHI
146.WebBrowser
147.WebBrowserTexture
148.WidgetCarousel
149.Windows
150.XmlParser
五.ThirdParty（第三方）
1.ADO
2.AMD
3.Android
4.asio
5.CEF3
6.coremod
7.Crunch
8.DirectShow
9.Eigen
10.Expat
11.Facebook
12.FBX
13.ForsythTriOO
14.FreeImage
15.FreeType2
16.glslang
17.GoogleARCore
18.GoogleGameSDK
19.GoogleInstantPreview
20.GoogleOboe
21.GooglePlay
22.GoogleTest
23.GoogleVR
24.HarfBuzz
25.HLMediaLibrary
26.hlslcc
27.ICU
28.Intel
29.IOS
30.jemalloc
31.Kiss_FFT
32.libcurl
33.libjpeg-turbo
34.libJPG
35.libOpus
36.libPhonon
37.libPNG
38.libSampleRate
39.libstrophe
40.libWebSockets
41.MCPP
42.MikkTSpace
43.mimalloc
44.mtlpp
45.NVIDIA
46.nvtesslib
47.nvTextureTools
48.nvTriStrip
49.Oculus
50.Ogg
51.openexr
52.OpenGL
53.OpenSSL
54.OpenSubdiv
55.OpenVR
56.OpenXR
57.Perforce
58.PhysX3
59.PLCrashReporter
60.portmidi
61.Python3
62.Qualcomm
63.rd_route
64.RenderDoc
65.rpclib
66.SDL2
67.ShaderConductor
68.SpeedTree
69.SPIRV-Reflect
70.Steamworks
71.VHACD
72.Vivox
73.Vorbis
74.Vulkan
75.WebRTC
76.Windows
77.WindowsMixedRealityInterop
78.WinHttp
79.zlib