UE4 C++ 从内存数据创建动态材质

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 spawned
void 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。