[Haskell-cafe] Problem with PDF/PS backend in GTK2HS

28 Oct 2007

      I have a strange problem, which is so elementary that I think I must be 
missing something...

In GTK2HS, when I draw text using using textPath, the text is located at 
different locations depending on which backend is used. I'm not talking 
about a difference of a couple of pixels , but in my case it's half a 
page off. The PNG and Win32 backend work fine, but the PDF/PS backends 
get it wrong.

For example, I modified the Text.hs demo in the demos/Cairo subdirectory 
so it also outputs PDF. Here the text is also at different locations, so 
I guess it's not just my code. Code is pasted below.

I'm using Windows, and GTK2HS version 0.9.12 from 
http://www.haskell.org/gtk2hs

Maybe someone could give this a quick test on Linux?

I guess this is most likely a Cairo problem, and has nothing to do with 
the Haskell wrapper? Still this is hard to believe, since these kinds of 
bugs would be quickly found.

Thanks,
Peter

----------------------------------------

import Graphics.Rendering.Cairo
import qualified Graphics.Rendering.Cairo.Matrix as M

boxText :: String -> Double -> Double -> Render ()
boxText text x y = do
  save

  lineWidth <- getLineWidth

  (TextExtents xb yb w h _ _) <- textExtents text

  rectangle (x + xb - lineWidth)
            (y + yb - lineWidth)
            (w + 2 * lineWidth)
            (h + 2 * lineWidth)
  stroke
  moveTo x y
  textPath text
  fillPreserve
  setSourceRGBA 0 0 1 0.5
  setLineWidth 3.0
  stroke

  restore

transpSurface :: Double -> Double -> Render ()
transpSurface w h = do
  save
  rectangle 0 0 w h
  setSourceRGBA 0 0 0 0
  setOperator OperatorSource
  fill
  restore

width = 400
height = 300

main :: IO ()
main = withImageSurface FormatARGB32 width height $ \surface -> do

  let render = do
        setSourceRGB 0.0 0.0 0.0
        setLineWidth 2.0

        transpSurface (fromIntegral width) (fromIntegral height)

        selectFontFace "sans" FontSlantNormal FontWeightNormal
        setFontSize 40

        extents <- fontExtents
        let fontHeight = fontExtentsHeight extents

        boxText "Howdy, world!" 10 fontHeight

        translate 0 fontHeight

        save
        translate 10 fontHeight
        rotate (10.0 * pi / 180.0)
        boxText "Yay for Haskell!" 0 0
        restore

        translate 0 (3 * fontHeight)

        save
        setFontMatrix $ M.rotate ((-10.0) * pi / 180.0) $ M.scale 40.0 
40.0 M.identity
        boxText "...and Cairo!" 10 fontHeight
        restore

  renderWith surface render

  surfaceWriteToPNG surface "Text.png"

  withPDFSurface "Text.pdf" (realToFrac width) (realToFrac height) (flip 
renderWith $ render >> showPage)

  return ()

[Haskell-cafe] Problem with PDF/PS backend in GTK2HS

Peter Verswyvelen