项目中经常需要对texture进行读写操作,所以做个总结。
方法1:
DynamicTexture = UTexture2D::CreateTransient(SizeX, SizeY); // Allocate the texture HRI DynamicTexture->UpdateResource(); // Use this function to update the texture rects you want to change: // NOTE: There is a method called UpdateTextureRegions in UTexture2D but it is compiled WITH_EDITOR and is not marked as ENGINE_API so it cannot be linked from plugins. void UpdateTextureRegions(UTexture2D* Texture, int32 MipIndex, uint32 NumRegions, FUpdateTextureRegion2D* Regions, uint32 SrcPitch, uint32 SrcBpp, uint8* SrcData, bool bFreeData) { if (Texture->Resource) { struct FUpdateTextureRegionsData { FTexture2DResource* Texture2DResource; int32 MipIndex; uint32 NumRegions; FUpdateTextureRegion2D* Regions; uint32 SrcPitch; uint32 SrcBpp; uint8* SrcData; }; FUpdateTextureRegionsData* RegionData = new FUpdateTextureRegionsData; RegionData->Texture2DResource = (FTexture2DResource*)Texture->Resource; RegionData->MipIndex = MipIndex; RegionData->NumRegions = NumRegions; RegionData->Regions = Regions; RegionData->SrcPitch = SrcPitch; RegionData->SrcBpp = SrcBpp; RegionData->SrcData = SrcData; ENQUEUE_UNIQUE_RENDER_COMMAND_TWOPARAMETER( UpdateTextureRegionsData, FUpdateTextureRegionsData*, RegionData, RegionData, bool, bFreeData, bFreeData, { for (uint32 RegionIndex = 0; RegionIndex < RegionData->NumRegions; ++RegionIndex) { int32 CurrentFirstMip = RegionData->Texture2DResource->GetCurrentFirstMip(); if (RegionData->MipIndex >= CurrentFirstMip) { RHIUpdateTexture2D( RegionData->Texture2DResource->GetTexture2DRHI(), RegionData->MipIndex - CurrentFirstMip, RegionData->Regions[RegionIndex], RegionData->SrcPitch, RegionData->SrcData + RegionData->Regions[RegionIndex].SrcY * RegionData->SrcPitch + RegionData->Regions[RegionIndex].SrcX * RegionData->SrcBpp ); } } if (bFreeData) { FMemory::Free(RegionData->Regions); FMemory::Free(RegionData->SrcData); } delete RegionData; }); } }
注意需要添加RHI和RenderCore模块,在4.17以后可以直接使用UTexture2D::UpdateTextureRegions。
方法2:
Texture = UTexture2D::CreateTransient(SizeX, SizeY); FTexture2DMipMap& Mip = [Texture]->PlatformData->Mips[Level]; void* Data = Mip.BulkData.Lock( LOCK_READ_WRITE ); FMemory::Memcpy( Data, NewData, DataSize ); Mip.BulkData.Unlock( ); Texture->UpdateResource();
这种方法每次调用都会Lock/UnLock,和updateResource,每次都会删除RHI Texture并重新创建,所以这种做法效率不高,最好不要在Tick等频率高得地方使用。而且UpdateResource只能在主线程中调用。
判断texture是否初始化用PullTextureTorS->IsValidLowLevel(),重新创建要注意把原有的texture删除。
PullTextureTorS->ConditionalBeginDestroy(); PullTextureTorS = UTexture2D::CreateTransient(width, height, PF_R8G8B8A8); PullTextureTorS->UpdateResource();
方法3:获取render target的数据
TArray<FColor> rawData; rawData.AddUninitialized(dataSize); FTextureRenderTargetResource* renderTarget = tempTexture->GameThread_GetRenderTargetResource(); renderTarget->ReadPixelsPtr((FColor*)rawData.GetData()); videoCapture->updateClientData((char *)rawData.GetData(), widht, height);
上述示例将rendertarget的数据拷贝到rawData,但是要注意ReadPixels这个操作很耗时,相当于把数据从GPU拷贝到CPU,而且会调用FlushingRenderCommand,这个函数会阻塞游戏线程,目前没有在UE4中找到更快的做法,Unity中倒是有将Rendertexture的数据给到一个Texture2D,unity的texture2d可能在CPU中有一份镜像,所以不太耗时。UE4中RHI接口,即RHICommanList中可能会找到如何实现比较快的获取到Rendertarget的数据。