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When you resize or move the viewing window in the Viewer, the program has to redraw the image on the screen. If you are working with a large cave or if you are using a special feature like Passage Wall Modeling, redrawing can take a long time. For this reason, the Viewer gives you complete control over how the redrawing is done.
Redrawing. There are two situations where a Windows program has to redraw the image on the screen. The first situation is where the contents of the window are changed. In the Viewer, this occurs when you zoom, pan or rotate the cave. In the second situation, the contents of the window doesn't change, but the window itself is changed. This occurs when the window is moved, resized or covered up by a menu or window. This means that every time you shift the position of the window on the screen, select a menu item, or change a setting; you may have to wait several seconds to restore the image. This is especially frustrating because the actual cave image has not changed.
Refresh Modes. There isn't much you can do about the first situation because the actual image has changed. However, there are several ways of dealing with the situation where the window is resized, moved or covered. As a result, the Viewer has three different "refresh" modes that control the way the screen is redrawn. You can change the Refresh mode by choosing one of the options in the "Option" from the menu. Here is a detailed description of each refresh mode:
1. Plot Refresh. When Plot Refresh Mode is on, the cave is redrawn by plotting each and every passage line. If the cave is large, the computer slow or you are using one of the passage modeling modes, this can take several seconds. Under ordinary circumstances, it is the fastest way to zoom, pan or rotate. The main disadvantage of this mode is that screen tends to flicker if you are manipulate the cave in real-time.
2. Hidden Refresh. In Hidden Refresh mode, the cave is drawn into “hidden memory” and then copied to the main screen. Because this copy operation is virtually instantaneous, changes appear to happen all at once. In other words, you don’t see screen begin erased or the individual passages being drawn and there is no flicker. This has the advantage of creating very smooth, movie-like pans, zooms and rotates. If you have a fast computer and video card, this option allows you to do Real Time Animations. The feature also has the advantage that it does not maximize the screen every time you change the image and it does not cause the tool windows to disappear.
The only disadvantage to this mode is that you can't see the image while it is being drawn so you don’t any way to gauge the progress. As a result, if the cave is very large or you are using one of the slower display features, there may be a long pause before the display changes.
3. Memory Refresh. When the Memory Refresh option is enabled, the program saves the whole screen image in memory whenever changes take place. This way, if the window changed, the program can just restore the image without having to draw each and every individual passage. This makes resizing, moving or uncovering the screen virtually instantaneous.
There are some disadvantages to Memory Refresh Mode. First, there is a slight pause to save the image any time you zoom or pan. This slight pause may slow the program slightly on a slow computer. Second, Memory Refresh maximizes the window so it fills the whole screen every time you zoom, pan, or rotate the image. This makes it hard to keep the window small and work with other programs. Finally, if you are using any of the special tools that are available in the Viewer, their windows will disappear momentarily whenever the screen is redrawn.