ImageDecoder-isFrameComplete.swift

func isFrameComplete(at index: Int) -> Bool {
    assert(frameCount > index)

    // CGImageSourceGetStatusAtIndex() changes the return status value from kCGImageStatusIncomplete
    // to kCGImageStatusComplete only if (index > 1 && index < frameCount() - 1). To get an accurate
    // result for the last frame (or the single frame of the static image) use CGImageSourceGetStatus()
    // instead for this frame.
    if index == frameCount - 1 {
        return CGImageSourceGetStatus(imageSource) == .statusComplete
    }

    return CGImageSourceGetStatusAtIndex(imageSource, index) == .statusComplete
}