KMM Creating Pixel Buffer from UIImage

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1

Hello there,
I am trying to solve an issue I’m having with creating a pixel buffer from a UIImage in Kotlin multiplatform.

My current system is setup with Kotlin as a common shared business logic (Core) and then swift running on top of it to handle the UI.

I am working with image processing on the Kotlin (core) layer.
During a capture session, I am sending frames into Core as UIImage’s.

I’m trying to create a CVPixelBuffer from the UIImage, but am getting stuck on creating the actual buffer object.

This is what my function looks like:

fun UIImage.getCVPixelBuffer(): CVPixelBufferRefVar? {
    val imageWidth = this.size.useContents { this.width }.toULong()
    val imageHeight = this.size.useContents { this.height }.toULong()
    val cgImage = this.CGImage

    val attDictionary = CFDictionaryCreateMutable(kCFAllocatorDefault, 2, null, null)
    CFDictionaryAddValue(attDictionary, kCVPixelBufferCGImageCompatibilityKey, kCFBooleanTrue)
    CFDictionaryAddValue(attDictionary, kCVPixelBufferCGBitmapContextCompatibilityKey, kCFBooleanTrue)

    // FAILING HERE -----------------
    // this ref needs to be initialized, but I can't figure out how ... ?
    val pixelBuffer: CVPixelBufferRefVar? = null
    CVPixelBufferCreate(
        kCFAllocatorDefault,
        imageWidth,
        imageHeight,
        kCVPixelFormatType_32ABGR,
        attDictionary,
        pixelBuffer?.ptr // this ptr does not exist yet :(((((
    )

    // condition will always fail since the pixelBuffer var is not properly given the value
    if (pixelBuffer !== null) {
        val flags = CVPixelBufferLockFlags.MIN_VALUE
        CVPixelBufferLockBaseAddress(pixelBuffer.value, flags)
        val pxdata = CVPixelBufferGetBaseAddress(pixelBuffer.value)

        val context = CGBitmapContextCreate(
            pxdata,
            imageWidth,
            imageHeight,
            8,
            CVPixelBufferGetBytesPerRow(pixelBuffer.value),
            CGColorSpaceCreateDeviceRGB(),
            CGImageAlphaInfo.kCGImageAlphaPremultipliedFirst.value
        )
        println("created context")

        if (context != null) {
            CGContextDrawImage(
                context,
                CGRectMake(
                    0.0,
                    0.0,
                    imageWidth.toDouble(),
                    imageHeight.toDouble()
                ),
                cgImage
            )
            println("drew image in context")
        } else {
            CVPixelBufferUnlockBaseAddress(pixelBuffer.value, flags)
            return null
        }

        CVPixelBufferUnlockBaseAddress(pixelBuffer.value, flags)
        return pixelBuffer
    } else {
        // always fails with this message :(
        println("pixelBufferRef is null after Create function")
    }

    return null
}

My best guess is that I need to somehow initialize the pixelBuffer: CVPixelBufferRefVar in order for it to be passed into the CVPixelBufferCreate() function correctly?

Any help would be appreciated!!