Scaled up MTKView shows gaps when joining CIImages - swift

Question

I'm using a MTKView written by Simon Gladman that "exposes an image property type of 'CIImage' to simplify Metal based rendering of Core Image filters." It has been slightly altered for performance. I left out an additional scaling operation since it has nothing to do with the issue here.
Problem: When creating a composite of smaller CIImages into a larger one, they are aligned pixel perfect. MTKView's image property is set to this CIImage composite. However, there is a scale done to this image so it fits the entire MTKView which makes gaps between the joined images visible. This is done by dividing the drawableSize width/height by the CIImage's extent width/height.
This makes me wonder if something needs to be done the CIImage side to actually join those pixels. Saving that CIImage to the camera roll shows no separation between the joined images. It's only visible when the MTKView scales up. In addition, whatever needs to be done needs to have virtually no impact on performance since these image renders are being done in real time through the camera's output. (The MTKView is a preview of the effect being done)
Here is the MTKView that I'm using to render with:
class MetalImageView: MTKView
{
let colorSpace = CGColorSpaceCreateDeviceRGB()
var textureCache: CVMetalTextureCache?
var sourceTexture: MTLTexture!
lazy var commandQueue: MTLCommandQueue =
{
[unowned self] in
return self.device!.makeCommandQueue()
}()!
lazy var ciContext: CIContext =
{
[unowned self] in
//cacheIntermediates
return CIContext(mtlDevice: self.device!, options:[.cacheIntermediates:false])
//return CIContext(mtlDevice: self.device!)
}()
override init(frame frameRect: CGRect, device: MTLDevice?)
{
super.init(frame: frameRect,
device: device ?? MTLCreateSystemDefaultDevice())
if super.device == nil
{
fatalError("Device doesn't support Metal")
}
CVMetalTextureCacheCreate(kCFAllocatorDefault, nil, self.device!, nil, &textureCache)
framebufferOnly = false
enableSetNeedsDisplay = true
isPaused = true
preferredFramesPerSecond = 30
}
required init(coder: NSCoder)
{
fatalError("init(coder:) has not been implemented")
}
/// The image to display
var image: CIImage?
{
didSet
{
//renderImage()
//draw()
setNeedsDisplay()
}
}
override func draw(_ rect: CGRect)
{
guard let
image = image,
let targetTexture = currentDrawable?.texture else
{
return
}
let commandBuffer = commandQueue.makeCommandBuffer()
let bounds = CGRect(origin: CGPoint.zero, size: drawableSize)
let originX = image.extent.origin.x
let originY = image.extent.origin.y
let scaleX = drawableSize.width / image.extent.width
let scaleY = drawableSize.height / image.extent.height
let scale = min(scaleX, scaleY)
let scaledImage = image
.transformed(by: CGAffineTransform(translationX: -originX, y: -originY))
.transformed(by: CGAffineTransform(scaleX: scale, y: scale))
ciContext.render(scaledImage,
to: targetTexture,
commandBuffer: commandBuffer,
bounds: bounds,
colorSpace: colorSpace)
commandBuffer?.present(currentDrawable!)
commandBuffer?.commit()
}
}
When compositing the images, I have a full size camera image as the background just as a foundation for what the size should be, then I duplicate half of that halfway across the width or height of the image using the CISourceAtopCompositing CIFilter and translate it using a CGAffineTransform. I also give it a negative scale to add a mirror effect:
var scaledImageTransform = CGAffineTransform.identity
scaledImageTransform = scaledImageTransform.translatedBy(x:0, y:sourceCore.extent.height)
scaledImageTransform = scaledImageTransform.scaledBy(x:1.0, y:-1.0)
alphaMaskBlend2 = alphaMaskBlend2?.applyingFilter("CISourceAtopCompositing",
parameters: [kCIInputImageKey: alphaMaskBlend2!,
kCIInputBackgroundImageKey: sourceCore])
alphaMaskBlend2 = alphaMaskBlend2?.applyingFilter("CISourceAtopCompositing",
parameters: [kCIInputImageKey: (alphaMaskBlend2?.cropped(to: cropRect).transformed(by: scaledImageTransform))!,
kCIInputBackgroundImageKey: alphaMaskBlend2!])
sourceCore is the original image that came through the camera. alphaMaskBlend2 is the final CIImage that I assign the MTKView to. The cropRect correctly crops the mirrored part of the image. In the scaled up MTKView there is a visible gap between these two joined CIImages. What can be done to make this image display as continuous pixels no matter how scaled the MTKView is just like any other image does?