func generatePDF() {
    let v1 = UIScrollView(frame: CGRectMake(0,0,100,100))
    let v2 = UIView(frame: CGRectMake(0,0,100,200))
    let v3 = UIView(frame: CGRectMake(0,0,100,200))
    v1.backgroundColor = UIColor.redColor()
    v1.contentSize = CGSize(width: 100, height: 200)
    v2.backgroundColor = UIColor.greenColor()
    v3.backgroundColor = UIColor.blueColor()

    let dst = NSHomeDirectory().stringByAppendingString("/sample1.pdf")
    // outputs as NSData
    do {
        let data = try PDFGenerator.generate([v1, v2, v3])
        data.writeToFile(dst, atomically: true)
    } catch (let error) {
        print(error)
    }

    // writes to Disk directly.
    do {
        try PDFGenerator.generate([v1, v2, v3], outputPath: dst)    
    } catch (let error) {
        print(error)
    }
}

public enum PDFPage {
    case WhitePage(CGSize) // = A white view
    case View(UIView)
    case Image(UIImage)
    case ImagePath(String)
    case Binary(NSData)
    case ImageRef(CGImage)
}

func generatePDF() {
    let v1 = UIView(frame: CGRectMake(0,0,100,100))
    v1.backgroundColor = UIColor.redColor()
    let v2 = UIView(frame: CGRectMake(0,0,100,200))
    v2.backgroundColor = UIColor.greenColor()

    let page1 = PDFPage.View(v1)
    let page2 = PDFPage.View(v2)
    let page3 = PDFPage.WhitePage(CGSizeMake(200, 100))
    let page4 = PDFPage.Image(UIImage(contentsOfFile: "path/to/image1.png")!)
    let page5 = PDFPage.ImagePath("path/to/image2.png")
    let pages = [page1, page2, page3, page4, page5]

    let dst = NSHomeDirectory().stringByAppendingString("/sample1.pdf")
    do {
        try PDFGenerator.generate(pages, outputPath: dst)
    } catch (let e) {
        print(e)
    }
}

public enum PDFGenerateError: ErrorType {
    case ZeroSizeView(UIView) // view's width or height is 0
    case ImageLoadFailed(String) // cannot load from image path
    case EmptyOutputPath // output path is empty
    case EmptyPage // Generate from empty page(s).
                   // `PDFGenerator.generate([])` isn't allowed.
}