BeginRefresh

Sets up a window for optimized refreshing.

Declaration

Source position: intuition.pas line 3513

Arguments

Description

This routine sets up your window for optimized refreshing.

Its role is to provide Intuition integrated access to the Layers library function BeginUpdate(). Its additional contribution is to be sure that locking protocols for layers are followed, by locking both layers of a WFLG_GIMMEZEROZERO window only after the parent Layer_Info has been locked. Also, the WFLG_WINDOWREFRESH flag is set in your window, for your information.

The purpose of BeginUpdate(), and hence BeginRefresh(), is to restrict rendering in a window (layer) to the region that needs refreshing after an operation such as window sizing or uncovering. This restriction to the "damage region" persists until you call EndRefresh().

For instance, if you have a WFLG_SIMPLE_REFRESH window which is partially concealed and the user brings it to the front, you can receive an IDCMP_REFRESHWINDOW message asking you to refresh your display. If you call BeginRefresh() before doing any of the rendering, then the layer that underlies your window will be arranged so that the only rendering that will actually take place will be that which goes to the newly-revealed areas. This is very performance- efficient, and visually attractive.

After you have performed your refresh of the display, you should call EndRefresh() to reset the state of the layer and the window. Then you may proceed with rendering to the entire window as usual.

You learn that your window needs refreshing by receiving either a message of class IDCMP_REFRESHWINDOW through the IDCMP, or an input event of class IECLASS_REFRESHWINDOW through the Console device. Whenever you are told that your window needs refreshing, you should call BeginRefresh() and EndRefresh() to clear the refresh-needed state, even if you don't plan on doing any rendering. You may relieve yourself of even this burden by setting the WFLG_NOCAREREFRESH flag when opening your window.

Warning:

You should only perform simple graphics refreshing operations between BeginRefresh() and EndRefresh(). These include any graphics.library drawing functions or the simple Intuition rendering functions (DrawImage(), PrintIText(), DrawBorder(), and so on). In particular, do not call RefreshGadgets(), RefreshGList(), RefreshWindowFrame(), etc., since any of the complex Intuition functions run the risk of creating a deadlock. Also avoid any other high-level calls in Intuition or ones that might invoke Intuition. This means no calling SetPointer(), no calling LockIBase(), no dos.library functions (since an EasyRequest() might result), etc. Keep it simple.

By the time the application receives its IDCMP_REFRESHWINDOW message, Intuition has already repaired any damaged regions of the window border or the gadgets in the window, so attempts to redraw gadgets or borders are as unnecessary as they are dangerous.

Another Warning:

The concept of multiple refresh passes using EndRefresh(w, False); is not completely sound without further protection. The reason is that between two sessions, more damage can occur to your window. Your final EndRefresh(w, True); will dispose of all damage, including the new, and your initial refreshing pass will never get the chance to refresh the new damage.

To avoid this, you must protect your session using LockLayerInfo() which will prevent Intuition from performing window operations or anything else which might cause further damage from occurring. Again, while holding the LayerInfo lock make no Intuition function calls dealing with gadgets; just render.

You can, however, call InstallClipRegion() for the different refresh passes, if you have two clip regions.

Similar Warning:

Your program and Intuition "share" your window layer's DamageList. BeginRefresh() helps arbitrate this sharing, but the lower-level function layers.library/BeginUpdate() does not. It isn't really supported to use BeginUpdate() on a window's layer, but if you do for whatever reason it is critical that you first acquire the LayerInfo lock as in the above example: even if you only have one pass of refresh rendering to do. Otherwise, the refreshing of your window's borders and gadgets can be incomplete, and the problem might occur only under certain conditions of task priority and system load.

See also