I am using the following code to export SceneCaptureComponent as a PNG image on the device and I am facing a weird issue. On Windows and iOS everything works as expected. On Android the image is upside down, like it is rotated by 180 degrees. Any hints why?
bool UsaveJPG::SaveImage(class USceneCaptureComponent2D* Target, const FString ImagePath, const FLinearColor ClearColour)
{
FRenderTarget* RenderTarget = Target->TextureTarget->GameThread_GetRenderTargetResource();
if (RenderTarget == nullptr)
{
return false;
}
TArray<FColor> RawPixels;
// Format not supported - use PF_B8G8R8A8.
if (Target->TextureTarget->GetFormat() != PF_B8G8R8A8)
{
// TRACEWARN("Format not supported - use PF_B8G8R8A8.");
return false;
}
if (!RenderTarget->ReadPixels(RawPixels))
{
return false;
}
// Convert to FColor.
FColor ClearFColour = ClearColour.ToFColor(false); // FIXME - want sRGB or not?
for (auto& Pixel : RawPixels)
{
// Switch Red/Blue changes.
const uint8 PR = Pixel.R;
const uint8 PB = Pixel.B;
Pixel.R = PB;
Pixel.B = PR;
// Set alpha based on RGB values of ClearColour.
Pixel.A = ((Pixel.R == ClearFColour.R) && (Pixel.G == ClearFColour.G) && (Pixel.B == ClearFColour.B)) ? 0 : 255;
}
TSharedPtr<IImageWrapper> ImageWrapper = ImageWrapperModule.CreateImageWrapper(EImageFormat::PNG);
const int32 Width = Target->TextureTarget->SizeX;
const int32 Height = Target->TextureTarget->SizeY;
if (ImageWrapper.IsValid() && ImageWrapper->SetRaw(&RawPixels[0], RawPixels.Num() * sizeof(FColor), Width, Height, ERGBFormat::RGBA, 8))
{
FFileHelper::SaveArrayToFile(ImageWrapper->GetCompressed(), *ImagePath);
return true;
}
return false;
}
It seems as if you aren't the only one having this issue.
Questions with answers (bolding to pop out answer section):
"I believe the editor mobile preview provides "correct" results, while the mobile device produces upside down results. I ran into this issue when creating a post process volume to simulate a camera partially submerged in water with mathematically calculated wave displacement. I can convert the screen position to world position using a custom material node with the code: float2 ViewPos = (ScreenPos.xy - View.ScreenPositionScaleBias.wz) / View.ScreenPositionScaleBias.xy * 10; float4 Pos = mul(float4(ViewPos, 10, 1), [Link Removed]); return Pos.xyz / Pos.w; This works as expected in the editor mobile preview, but the results are weirdly flipped around when launching to a mobile device. Manually inverting the Y-coordinate of the UV by subtracting the Y-component from 1 will correct the ViewportUV output, but the world space calculation still doesn't work (probably because [Link Removed] and [Link Removed]need to also be inverted). Strangely, if I feed the inverted UV coordinates into SceneTexture:PostProcessInput0, the entire scene flips upside down when running on a mobile device. This means that the ScreenPosition's ViewportUV is not the same as the SceneTexture UV. As a result, any post process effects that rely on the ViewportUV do not work correctly when running on mobile devices."
https://unreal-engine-issues.herokuapp.com/issue/UE-63442
I'm having trouble getting the tilt function to work with my Android phone. It seems that the tilt values are upside down because when I hold the phone flat on the table with the screen up, the tilt values snap from values like x=-3,y=0,z=-3 to z=3,y=0,z=3. When I hold the phone up with the screen facing down, the values are much closer to 0 all round.
Response:
tilt Y is always zero on android devices. but works fine on IOS
I think nobody has reported it as bug yet :) you do it
I'm not an Unreal dev, but you might have to put in a condition for Android to invert the image for yourself. I've done that kind of thing before (think cross browser compatibility). It's always a PITA and bloats the code for a stupid "reason", but sometimes it's what you have to do. Maybe Unreal will release a patch for it, but not likely, since any other devs who've already accepted and accounted for this issue will now have to fix their "fixed" code. It may just have to be something you live with, unfortunately.
With reading this, it just sounds like the different OSs decided on different corners for the origin of the "graph" that is the screen. Win and iOS seem to have chosen the same corner, while Android chose differently. I've done similar things in programming as well as for CNC machines. You may be able to choose your "world origin" and orientation in setting.
https://docs.unrealengine.com/en-US/Platforms/AR/HandheldAR/ARHowToShowWorldOrigin/index.html
There's not much out there that I can decipher being relevant, but searching for "android unreal world origin" gets a few results that might help. And adding "orientation" gets some different, possibly relevant, results.