C: GTK: invert foreground and background colours.

adz · 08-29-2008, 12:33 AM

Hi there.

I'm brushing up on my C by learning some GTK and I'm trying to find a way to invert foreground and background colours on a particular widget of mine (EventBox + Label). I thought an easy way of doing this would be to get the current fg/bg colours and swap them around. I know how to SET colours using gtk_widget_modify_bg () and gtk_widget_modify_fg () but I don't know how to determine what colours are being used by default so that I can supply the reverse to the gtk_widget_modify_* functions.

If anyone knows how to do this or thinks that there is a better way to achieve what I'm trying to do, I'd like to hear from you.

Thanks in advance.

wget · 08-30-2008, 12:11 PM

I've been looking at Gtk myself so pretty much a novice in it but I had a look at the docs and managed to swap the colours using the widgets styles. Do know if this is the best way but it's one way. This is the callback function I used:

Code:

static gboolean button_pressed(GtkWidget* eventbox, GdkEventButton* event, GtkLabel* label){

	GdkColor   *eventbox_background, *label_foreground;
	GtkStyle*  label_style;

	eventbox_background = eventbox->style->bg;
	
	label_style = gtk_widget_get_style( GTK_WIDGET(label) );
	label_foreground = label_style->fg;

	gtk_widget_modify_bg( eventbox, GTK_STATE_NORMAL, label_foreground);
	
	gtk_widget_modify_fg( GTK_WIDGET(label), GTK_STATE_NORMAL, eventbox_background);

}

adz · 08-31-2008, 02:08 AM

Thanks. That worked, but not without some possible dodginess. You see, my app is hidden by default and only appears when you click the systray icon (it's a calendar app). So, before I can extract the appropriate styles, I need to quickly call gtk_widget_show () followed by gtk_widget_hide () for GTK to "refresh" it's memory about what the current theme actually is. If I don't do this I get fg = black and bg = white always. My default theme is a dark background with light text so it's really apparent when GTK gets it wrong.

Do you have any experience with this? Is what I've done acceptable? It works, that much is clear, but I'm not sure if there isn't a cleaner, more efficient way of doing this or if there may be unintended consequences in doing things this way.