ruby-****@sourc*****
ruby-****@sourc*****
2013年 3月 20日 (水) 03:35:38 JST
-------------------------
REMOTE_ADDR = 184.145.81.215
REMOTE_HOST =
URL = http://ruby-gnome2.sourceforge.jp/hiki.cgi?tut-gtk2-dancr-intro
-------------------------
@@ -15,3 +15,5 @@
Up to this chapter, in this tutorial, we have become reasonably familiar with our Ruby GUI based on pure GTK. However, even in the area of pure GTK without the Cairo library, many things are still shrouded in mystery. Most noticeably, we are considerably inexperienced and lacking most of the details, of how any kind of drawing is stored in the memory, when only different parts of it should be removed and redone, and most importantly, how it changes with time, as a user draws or deletes parts of the larger drawing, graphic piece or image. Not surprisingly, we are also very poorly acquainted with the backgrounds onto which one draws or paints, as well as with understanding of what a drawing or an image is. For instance, is it an object on its own, or does the drawn item become a part of the background when finally drawn, painted, or rendered onto the 'drawable'? Therefor, when GTK was augmented with Cairo graphics library, which itself contains its own drawable backgrounds, it
becomes necessary to learn what are the relationships between these drawable areas and drawn/painted images in either of these two environments.
The best way to get introduced to these issues is by trying to tackle the real life graphic programming issues related to background surfaces to which a user should be able to draw, paint or programmatically generate geometric shapes, and miscellaneous images, and most importantly from which he or she should also be able to remove drawings and/or images after they were drawn, painted or copied and rendered to the electronic surfaces and/or devices, most often, but not exclusively, the computer screens. This latest functionality in most GUI environments is dubbed "undoing" and/or "redoing".
+
+We have indeed, just slightly, already touched on these issues in chapter 11 on paragraph 11.1 "((<Drawing Widgets|tut-gtk2-agtkw-draww>))" discussing program called 'drawingareas.rb', suggesting you get familiar with the way user interactions may cause a drawing area to be redrawn (actually cleared, and how the programmer must make sure the drawn items do not get lost) when window is moved, resized, or even when focus is changed on widgets and windows. The program also implements the most basic "redo" functionality, by allowing user to clear the screen by pressing the Delete key. Though, this is far from what the full-blown "undo/redo" functionality would look like, it is the absolute requirement you understand the two, namely, manual clearing of the drawing area on the one hand, and the automatic clearing/redrawing of the window when 'expose-event' is emitted.