John, For someone relatively new to GTK like myself, the thread of messages from you, Richard Boaz, and Paul Davis was extremely eye-opening but also confusing. I am grateful to hear the exchange of ideas, to the extent that I understood it. The confusing part is simply trying to decide which of the design principles makes sense for what I am trying to do now, but also trying to extrapolate and understand what principles to follow in general when starting up a new application. I am not fishing for answers here; this problem is mine. I do still have one question about a specific suggestion that you made in this thread, below: > -----Original Message----- > From: jcupitt@xxxxxxxxx [mailto:jcupitt@xxxxxxxxx] > Sent: Thursday, November 29, 2007 4:48 PM > > -- snip -- > > This is often not the case, especially in a complex application. > Instead, you should think of your window as being composed from a > number of separate layers (like photoshop layers), and that on an > expose you should completely repaint that section of the window by > drawing all layers from the back forwards. > > -- snip -- > > Assuming it's raster, you should have two separate data structures. > Keep a large image around which has the current state of your user's > image. Only drawing operations go into this, no rubberbanding. This is > your background layer. Rubberband operations are in another layer > which floats on top of this. Do you mean a second pixmap? If so, how does one draw the second one on top of the first without replacing pixels, assuming the GC function is just GDK_COPY? > > On an expose, use your background image to paint the exposed pixels. > Then, if there's a rubber band active at the moment and if the > bounding box of the rubber band intersects the expose, draw that as > well on top of the image. How does one draw layers "on top of" layers? If I am understanding you correctly, you are saying that I can use one bg pixmap to store one layer, and another pixmap to store a second, higher layer. To be precise, suppose that I have added the original scribble example, tools so that the user can draw shapes in addition to the brush strokes. I keep the drawing the user has created so far in a bg pixmap. Now the user wants to put a line on top of that drawing, and I want to rubberband it. Are you saying that (1) the rubberbanded line is drawn into a second pixmap that is drawn "on top of" the other, and if so, how does one draw on top without obscuring the pixels underneath using a straightforward GDK_COPY function in the gc, or (2) do you mean that I should draw into the window, not a second pixmap, after I have drawn the bg pixmap underneath it? I have tried drawing directly into the window for the rubberbanded line, and sending an invalidate_rect event for that line to force a redraw of the rectangle that includes it as I move the mouse, to make it "disappear", but the result is that it disappears so fast that it is not visible. Could you clarify? Thanks Stewart _______________________________________________ gtk-list mailing list gtk-list@xxxxxxxxx http://mail.gnome.org/mailman/listinfo/gtk-list
