I don't know if anyone has worked on #257685 yet. I gave it a quick look and maybe the fix is very simple.
Apparently with Gtk2.13 and greater, Gtk is enforcing the page size and steps, which seems to be the root of the problem where the sliders can only max out to 245 rather than 255. If [0..255] were a document, 245 would be the bottom of the last page, so the adjustment widget is operating correctly.
According to the Gtk notes, setting page sizes and steps to 0 for simple adjusters might be the best way to fix this.
In src/widgets/sp-color-slider.cpp, line 332, this little modification seems to fix the problem:
if (!adjustment) { adjustment = (GtkAdjustment *) gtk_adjustment_new (0.0, 0.0, 1.0, 0.01, 0.0, 0.0); } //in case of existing adjustment gtk_adjustment_set_page_increment(adjustment, 0.0); gtk_adjustment_set_page_size(adjustment, 0.0);
Maybe someone with knowledge of the older SP-vintage widgets can decide if this is a valid fix or is merely fixing the symptom? I'd rather not commit with insufficient knowledge of how this thing works.
bob (ishmal)