Reading pixel color from texture, random memcpy error


I am trying to read the pixel colors from a texture. After many hours, I finally have something that works in shipping builds. Well, half of the time. Both in the editor and in packaged builds, my code crashes ~50% of the time.

I use the same texture and settings. When I stepped through the code, the texture and other pointers seemed to be valid every time, so I have no clue why the ‘memcpy’ line keeps crashing randomly with an access violation error.

FTexture2DMipMap* MipMap = &inTexture->PlatformData->Mips[0];
FByteBulkData* RawImageData = &MipMap->BulkData;
const FColor* ImageData = reinterpret_cast<const FColor*>(RawImageData->Lock(LOCK_READ_ONLY));

const int32 NumPixels = inTexture->GetSizeX() * inTexture->GetSizeY();

FMemory::Memcpy(outPixelColors.GetData(), ImageData, NumPixels * sizeof(FColor)); //crashing ~50% of the time

Any ideas or help would be appreciated!

Maybe it is a source version difference (I’m on 4.27), but you FMemory::Memcpy call looks weird to me.

It looks like you are using the non-templated version of that function, but you are calling it with types that do not implicitly cast to void*, so I’m not sure how you got this to compile.

Since you are calling the void* version that includes the number of bytes for the size of the copy, the problem is likely because your destination is not the correct size.

If you’ve confirmed that to not be the case, then your source pointer might be wrong, or you are copying too much from the source pointer.

If you confirmed that all of those are fine, then it might be a lifetime issue related to outPixelColors. Perhaps when this code runs there is a race condition with the lifetime of outPixelColors that results the access violation.

If you confirmed that none of those things are happening. Well, that is a head scratcher. Put some check()s in to make sure that you are 100% sure 100% of the time that all of the above things are good. If it still gives you random crashes… that would be an interesting puzzle.