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