UE4 C++ 从内存数据创建动态材质

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动态材质的创建

需要注意的是，本文写的是根据二进制数据流创建动态材质，而不是单纯的用C++加载一个材质并赋予模型。项目有需求需要把视频采集卡采集到的视频在UE4里显示，所以简单研究了一下。

我的目的是把用第三方硬件的SDK开发出来的程序写的数据流创建为动态材质，所以如何把采集到的视频写成数据流不再考虑范围内，我们直接用就好了。

unsigned int CaptureChannels::readChannelData(unsigned int cardId, unsigned int channelId, unsigned char *buffer, unsigned int &length){    unsigned int idx = cardId * MAX_CHANNEL_NUM_PER_CARD + channelId;    memcpy(buffer, channelData[idx].buffer, channelData[idx].buflen);    length = channelData[idx].buflen;    return channelData[idx].seqNo;}

所以，我们只要把数据从buffer从还原为图片在构建贴图就好了。

在UE4中新建一个Actor类，因为要往场景中放置，材质要在模型上显示。然后新建一个材质并把它的texture节点参数化再继承它的材质实例。
在头文件中声明变量

    UPROPERTY(EditAnywhere, Category = Mesh)    class UStaticMeshComponent* MeshScreen;    unsigned char *buffer;    UTexture2D *m_texture;    UMaterialInterface *ScreenMaterial;    UMaterialInstanceDynamic *DynamicMaterial;

在源文件中的构造函数和BeginPlay函数中完成初始化操作

ACaptureActor::ACaptureActor(){    // Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.    PrimaryActorTick.bCanEverTick = true;    MeshScreen = CreateDefaultSubobject<UStaticMeshComponent>(TEXT("Mesh1P"));    buffer = new unsigned char[2048 * 2048 * 4];}// Called when the game starts or when spawnedvoid ACaptureActor::BeginPlay(){    Super::BeginPlay();    FString path = "/Game/Mesh/phong1.phong1";    ScreenMaterial = Cast<UMaterialInterface>(StaticLoadObject(UMaterialInterface::StaticClass(), nullptr, *path));    DynamicMaterial = UMaterialInstanceDynamic::Create(ScreenMaterial, this);    CaptureChannels::Instance()->readConfig();    CaptureChannels::Instance()->initCaputre();    m_texture = UTexture2D::CreateTransient(1024, 512);}

CaptureChannels的相关操作不用理会。然后编写核心函数并在Tick中调用。

void ACaptureActor::setTextureFromLoadImg(bool bWasSuccessful){    unsigned int  len = 0;    CaptureChannels::Instance()->run();    CaptureChannels::Instance()->readChannelData(0, 0, buffer, len);    //FUpdateTextureRegion2D *Region2D = new FUpdateTextureRegion2D(0, 0, 0, 0, 1024, 512);    //m_texture->UpdateTextureRegions(0, 1, Region2D, 1, 4, buffer, test);    void* temp_dataPtr = m_texture->PlatformData->Mips[0].BulkData.Lock(LOCK_READ_WRITE);    FMemory::Memcpy(temp_dataPtr, buffer, len);    m_texture->PlatformData->Mips[0].BulkData.Unlock();    m_texture->UpdateResource();    DynamicMaterial->SetTextureParameterValue("TextureScreen", m_texture);    MeshScreen->SetMaterial(0, DynamicMaterial);}

我注释掉的两行代码是UE4的API，从4.9到现在有了很大的改变，理论上是可以直接用的，我没有找到用法，知道的朋友请不吝赐教。大体思路是，先在UE4里创建材质和材质实例，然后在C++中修改参数。

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