How to change properties of DrawingArea in Gtk2Hs - haskell

Question

Can someone please point me in the right direction when it comes to changing properties of an element in Gtk2Hs.
For example, how do I change the background-color of a DrawingArea?

Answer 1

There are various methods for modifying a widget's style. For example to modify the background style you can use widgetModifyBg (corresponding to the C function gtk_widget_modify_bg()). In principle, if you change the style for one state (e.g. StateNormal) then you should also change it for the others.
Y would suggest you describe the styles you want in an RC file, and then load that file from your application, but it seems that functions like gtk_rc_parse() are not bound in gtk2hs.
Here's an example:
import Graphics.UI.Gtk
main = do
initGUI
window <- windowNew
window `onDestroy` mainQuit
drawingArea <- drawingAreaNew
window `containerAdd` drawingArea
widgetModifyBg drawingArea StateNormal (Color 0xffff 0 0)
widgetShowAll window
mainGUI
If you need to do custom drawing based on a widget's styles, you can do that using widgetGetState, the widgetStyle property and the styleGet* family of functions (e.g. styleGetText). Here's an example of that:
import Graphics.Rendering.Cairo
import Graphics.UI.Gtk hiding (fill)
import Graphics.UI.Gtk.Gdk.Events (Event(Expose))
expose widget rect = do
state <- widgetGetState widget
style <- widget `get` widgetStyle
(Color red green blue) <- styleGetText style state
drawWindow <- widgetGetDrawWindow widget
renderWithDrawable drawWindow $ do
moveTo 50 50
setFontSize 20
setSourceRGB (fromIntegral red / 0xffff)
(fromIntegral green / 0xffff)
(fromIntegral blue / 0xffff)
showText "O HAI"
fill
return False
main = do
initGUI
window <- windowNew
window `onDestroy` mainQuit
drawingArea <- drawingAreaNew
drawingArea `onExpose` \(Expose sent area region count) ->
expose drawingArea area
window `containerAdd` drawingArea
widgetShowAll window
mainGUI