Cached-Micro Presentation Spaces

The cached-micro presentation space provides the simplest and most efficient drawing environment. It can be used only for drawing on the screen, typically in the context of a window. It is most appropriate for application tasks that require simple window-drawing functions that will not be printed. Cached-micro presentation spaces do not support retained graphics.

After an application draws to a cached-micro presentation space, the drawing commands are routed through an implied device context to the current display. The application does not require information about the actual device context, because the device context is assumed to be the display. This process makes cached-micro presentation spaces easy for applications to use. The following code fragment illustrates this process:

       HPS    hps;

            case WM_PAINT:
                hps = WinBeginPaint(hwnd,NULL,NULL);

                /*
                 * Use PS.
                 */

                WinEndPaint (hps);

or

        HPS    hps;

            case WM_PAINT:

                 hps = WinGetPS(hwnd);

                 /*
                 * Use PS.
                 */

                 WinReleasePS(hps);

There are two common strategies for using cached-micro presentation spaces in an application. The simplest strategy is to call the WinBeginPaint function during the WM_PAINT message, use the resulting cached-micro presentation space to draw in the window, then return the presentation space to the system by calling the WinEndPaint function. By using this method, the application interacts with the presentation space only when drawing in the presentation space. This method is most appropriate for simple drawing. A disadvantage of this method is that the application must set up any special attributes for the presentation space, such as line color and font, each time a new presentation space is obtained.

A second strategy is for the application to allocate a cached-micro presentation space during initialization, by calling the WinGetPS function and saving the resulting presentation-space handle in a static variable. Then the application can set attributes in the presentation space that exist for the life of the program. The presentation-space handle can be used as an argument to the WinBeginPaint function each time the window gets a WM_PAINT message; the system modifies the visible region and returns the presentation space to the application with its attributes intact. This strategy is appropriate for applications that need to customize their window-drawing attributes. A presentation space that is obtained by calling the WinGetPS function must be released by calling WinReleasePS when the application has finished using it, typically during program termination. A presentation space that is obtained by calling WinBeginPaint must be released by calling WinEndPaint, typically as the last part of processing a WM_PAINT message.