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Simple example of rendering diagrams to a GTK window. Being an updated version of https://groups.google.com/forum/#!topic/diagrams-discuss/IWSGyN--AlM
{-# LANGUAGE NoMonomorphismRestriction #-}
{- | A first example of drawing diagrams from within GTK. This
program draws a Koch snowflake with the depth controllable
via a GTK widget.
-}
module Main where
import Graphics.UI.Gtk
import Diagrams.Prelude
import Diagrams.TwoD.Size (requiredScaleT)
import Diagrams.Backend.Gtk
import Diagrams.Backend.Cairo (Cairo)
import qualified Data.Colour as C
-- Our drawing code, copied from
-- projects.haskell.org/diagrams/gallery/Pentaflake.html
colors = iterate (C.blend 0.1 white) blue
p = regPoly 5 1 # lwO 0
-- | create a snowflake diagram of depth @n@
--
-- specifying a type here because the monoidal query type needs to be specified
-- for @drawToGtk@, otherwise get a "No instance for (PathLike ..." error.
pentaflake :: Int -> Diagram Cairo R2
pentaflake 0 = p
pentaflake n = appends (p' # fc (colors !! (n-1)))
(zip vs (repeat (rotateBy (1/2) p')))
where vs = take 5 . iterate (rotateBy (1/5))
. (if odd n then negateV else id) $ unitY
p' = pentaflake (n-1)
pentaflake' n = pentaflake n # fc (colors !! n)
-- end of diagrams code
-- A function to set up the main window and signal handlers
createMainWindow = do
win <- windowNew
onDestroy win mainQuit
drawArea <- drawingAreaNew
depthWidget <- spinButtonNewWithRange 1 10 1
-- when the spinButton changes, redraw the window
depthWidget `onValueSpinned` (widgetQueueDraw drawArea)
-- handle the drawArea's @onExpose@ signal. We provide a function
-- that takes an area marked as dirty and redraws it.
-- This program simply redraws the entire drawArea.
--
-- Many gtk signal handlers return True if the signal was handled, and False
-- otherwise (in which case the signal will be propagated to the parent).
drawArea `onExpose` \_dirtyRect -> do
-- can't draw to a drawArea directly (this is a limitation of gtk2hs),
-- so first we retrieve the drawWindow and render to that instead.
-- Drawing to GTK requires that we manually specify the size
-- and positioning,
--
-- however we can use @adjustSize@ to calculate the necessary rescaling
-- for a full-scale image
--
-- the @toGtkCoords@ function performs two tasks. It centers the diagram
-- in the drawWindow, and reflects it about the Y-axis. The Y-axis
-- reflection is due to an orientation mismatch between Cairo and
-- diagrams.
(canvasX,canvasY) <- widgetGetSize drawArea -- size in pixels (Int)
curDepth <- spinButtonGetValueAsInt depthWidget
let dia = pentaflake curDepth
fI = fromIntegral
spec = mkSizeSpec (Just $ fI canvasX) (Just $ fI canvasY)
scaledDia = toGtkCoords $ transform (requiredScaleT spec (size2D dia)) dia
drawWindow <- widgetGetDrawWindow drawArea
renderToGtk drawWindow scaledDia
return True
-- add the depthWidget control and drawArea to the main window
hbox <- hBoxNew False 0
boxPackStart hbox depthWidget PackNatural 0
boxPackStart hbox drawArea PackGrow 0
containerAdd win hbox
return win
-- Gtk application
--
-- initial the library, create and show the main window,
-- finally enter the main loop
main :: IO ()
main = do
initGUI
win <- createMainWindow
widgetShowAll win
onDestroy win mainQuit
onSizeRequest win $ return (Requisition 200 200) -- request minimum size
mainGUI
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