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                Using Coordinate Spaces and Transformations
 
You can perform the following tasks by using the coordinate-space and
transformation functions:
 
♦  Set an application's drawing units to convenient units.
 
♦  Scroll and zoom a picture.
 
♦  Rotate, scale, and shift an object in a picture.
 
Setting Convenient Drawing Units
 
You can use the GpiCreatePS function to set the device transformation so
that it uses more convenient page units──for example, centimeters. Follow
these steps:
 
1  If the output device is a screen, open a device context by calling the
   WinOpenWindowDC function. (If the output device is a printer or plotter,
   open a printer or plotter device context by calling the DevOpenDC
   function.)
 
2  Create a presentation space by calling the GpiCreatePS function,
   specifying low-metric page units and associating the device context with
   the presentation space.
 
The following code fragment demonstrates these steps:
 
HDC hdc;         /* device-context handle       */
HWND hwndClient; /* client-window handle        */
SIZEL sizlPage;  /* presentation-page rectangle */
HAB hab;         /* anchor-block handle         */
HPS hps;         /* presentation-space handle   */
    .
    .
    .
hdc = WinOpenWindowDC(hwndClient);
sizlPage.cx = 0;
sizlPage.cy = 0;
hps = GpiCreatePS(hab,
    hdc,           /* device-context handle        */
    &sizlPage,     /* address of SIZEL structure   */
    PU_LOMETRIC    /* centimeters as page units    */
    | GPIA_ASSOC); /* associates window DC with PS */
 
Zooming a Picture
 
You can use the GpiSetDefaultViewMatrix function to zoom a picture. The
following code fragment shows how to zoom out to ¼ or 1/8 scale by using the
default viewing transformation:
 
/* Zoom 1/8 */
 
matlfTransform.fxM11 = MAKEFIXED(0, 8192);
matlfTransform.fxM12 = MAKEFIXED(0, 0);
matlfTransform.lM13 = 0L;
matlfTransform.fxM21 = MAKEFIXED(0, 0);
matlfTransform.fxM22 = MAKEFIXED(0, 8192);
matlfTransform.lM23 = 0L;
matlfTransform.lM31 = 0L;
matlfTransform.lM32 = 0L;
matlfTransform.lM33 = 1L;
GpiSetDefaultViewMatrix(hps, 9L, &matlfTransform, TRANSFORM_REPLACE);
 
/* Zoom 1/4 */
 
matlfTransform.fxM11 = MAKEFIXED(0, 16384);
matlfTransform.fxM12 = MAKEFIXED(0, 0);
matlfTransform.lM13 = 0L;
matlfTransform.fxM21 = MAKEFIXED(0, 0);
matlfTransform.fxM22 = MAKEFIXED(0, 16384);
matlfTransform.lM23 = 0L;
matlfTransform.lM31 = 0L;
matlfTransform.lM32 = 0L;
matlfTransform.lM33 = 1L;
GpiSetDefaultViewMatrix(hps, 9L, &matlfTransform, TRANSFORM_REPLACE);
 
Rotating an Object in a Picture
 
To rotate an object in a world space by using the model transformation, you
must perform the following steps:
 
1  Translate the object over the coordinate-space origin.
2  Rotate the object.
3  Translate the object back to its original position.
4  Draw the object.
 
The following code fragment rotates a box 45 degrees:
 
/* translates, rotates 45 degrees, translates */
 
matlfTransform.fxM11 = MAKEFIXED(1, 0);
matlfTransform.fxM12 = MAKEFIXED(0, 0);
matlfTransform.lM13 = 0L;
matlfTransform.fxM21 = MAKEFIXED(0, 0);
matlfTransform.fxM22 = MAKEFIXED(1, 0);
matlfTransform.lM23 = 0L;
matlfTransform.lM31 = -150L;      /* translates box 150 units left */
matlfTransform.lM32 = -150L;      /* translates box 150 units down */
matlfTransform.lM33 = 1L;
GpiSetModelTransformMatrix(hps, 9L, &matlfTransform,
    TRANSFORM_REPLACE);
 
matlfTransform.fxM11 = MAKEFIXED(0, 46340);  /* cos 45 * 65536  */
matlfTransform.fxM12 = -MAKEFIXED(0, 46340); /* -sin 45 * 65536 */
matlfTransform.lM13 = 0L;
matlfTransform.fxM21 = MAKEFIXED(0, 46340);  /* sin 45 * 65536  */
matlfTransform.fxM22 = MAKEFIXED(0, 46340);  /* cos 45 * 65536  */
matlfTransform.lM23 = 0L;
matlfTransform.lM31 = 0L;
matlfTransform.lM32 = 0L;
matlfTransform.lM33 = 1L;
GpiSetModelTransformMatrix(hps, 9L, &matlfTransform, TRANSFORM_ADD);
 
matlfTransform.fxM11 = MAKEFIXED(1, 0);
matlfTransform.fxM12 = MAKEFIXED(0, 0);
matlfTransform.lM13 = 0L;
matlfTransform.fxM21 = MAKEFIXED(0, 0);
matlfTransform.fxM22 = MAKEFIXED(1, 0);
matlfTransform.lM23 = 0L;
matlfTransform.lM31 = 150L;    /* shifts back to original pos. */
matlfTransform.lM32 = 150L;    /* shifts back to original pos. */
matlfTransform.lM33 = 1L;
GpiSetModelTransformMatrix(hps, 9L, &matlfTransform, TRANSFORM_ADD);
 
 
                                      ♦