Translating, Rotating, and Scaling a Picture

GpiTranslate, GpiRotate, and GpiScale provide a convenient method for transforming objects in a picture. The following figure shows how to use these functions to translate, rotate, and scale a triangle.

    MATRIXLF matlfTransform;
    POINTL ptlStart, ptlTrans, ptlRotate, ptlScale;
    FIXED fxAngle, afxScale[2];
    POINTL aptlTriangle[] = { 575, 300, 575, 500, 500, 300 };

    ptlStart.x = 500;                      /* Starting point x direction   */
    ptlStart.y = 300;                      /* Starting point y direction   */
    GpiMove(hps, &ptlStart);
    GpiPolyLine(hps, sizeof(aptlTriangle) / sizeof(POINTL), aptlTriangle);

    ptlTrans.x = 75;                       /* x coordinate for translation */
    ptlTrans.y = 75;                       /* y coordinate for translation */

    GpiTranslate(hps,                      /* Presentation-space handle    */
        &matlfTransform,                   /* Address of matrix            */
        TRANSFORM_REPLACE,                 /* Replace old matrix with new  */
        &ptlTrans);                        /* Coordinates for translation  */

    GpiSetModelTransformMatrix(hps,        /* Presentation-space handle    */
        9,                                 /* Number of points in matrix   */
        &matlfTransform,                   /* Address of matrix            */
        TRANSFORM_REPLACE);                /* Replace old matrix with new  */

    GpiMove(hps, &ptlStart);               /* Move to starting point       */
    GpiPolyLine(hps, sizeof(aptlTriangle) / sizeof(POINTL), aptlTriangle);

    fxAngle = MAKEFIXED(-45, 0);           /* Rotate 45 degrees clockwise  */
    ptlRotate.x = 550;                     /* x coordinate rotation origin */
    ptlRotate.y = 350;                     /* y coordinate rotation origin */

    GpiRotate(hps,                         /* Presentation-space handle    */
        &matlfTransform,                   /* Address of matrix            */
        TRANSFORM_REPLACE,                 /* Replace old matrix with new  */
        fxAngle,                           /* Rotation angle               */
        &ptlRotate);                       /* Origin of rotation           */

    GpiSetModelTransformMatrix(hps, 9, &matlfTransform, TRANSFORM_REPLACE);

    GpiMove(hps, &ptlStart);               /* Move to starting point       */
    GpiPolyLine(hps, sizeof(aptlTriangle) / sizeof(POINTL), aptlTriangle);

    ptlScale.x = 550;                      /* x coordinate scale origin    */
    ptlScale.y = 350;                      /* y coordinate scale origin    */
    afxScale[0] = MAKEFIXED(2, 0);         /* Scaling factor on x axis     */
    afxScale[1] = MAKEFIXED(2, 0);         /* Scaling factor on y axis     */

    GpiScale(hps,                          /* Presentation-space handle    */
        &matlfTransform,                   /* Address of matrix            */
        TRANSFORM_REPLACE,                 /* Replace old matrix with new  */
        &afxScale[0],                      /* Scaling factor               */
        &ptlScale);                        /* Origin of scaling operation  */

    GpiSetModelTransformMatrix(hps, 9, &matlfTransform, TRANSFORM_REPLACE);

    GpiMove(hps, &ptlStart);               /* Move to starting point       */
    GpiPolyLine(hps, sizeof(aptlTriangle) / sizeof(POINTL), aptlTriangle);