LISTING 51.1 L51-1.C

/* 3D animation program to view a cube as it rotates in Mode X. The viewpoint
   is fixed at the origin (0,0,0) of world space, looking in the direction of
   increasingly negative Z. A right-handed coordinate system is used throughout.
   All C code tested with Borland C++ in C compilation mode. */
#include <conio.h>
#include <dos.h>
#include <math.h>
#include “polygon.h”

#define ROTATION  (M_PI / 30.0)  /* rotate by 6 degrees at a time */

/* base offset of page to which to draw */
unsigned int CurrentPageBase = 0;
/* Clip rectangle; clips to the screen */
int ClipMinX=0, ClipMinY=0;
int ClipMaxX=SCREEN_WIDTH, ClipMaxY=SCREEN_HEIGHT;
/* Rectangle specifying extent to be erased in each page. */
struct Rect EraseRect[2] = { {0, 0, SCREEN_WIDTH, SCREEN_HEIGHT},
   {0, 0, SCREEN_WIDTH, SCREEN_HEIGHT} };
static unsigned int PageStartOffsets[2] =
   {PAGE0_START_OFFSET,PAGE1_START_OFFSET};
int DisplayedPage, NonDisplayedPage;
/* Transformation from cube’s object space to world space. Initially
   set up to perform no rotation and to move the cube into world
   space -100 units away from the origin down the Z axis. Given the
   viewing point, -100 down the Z axis means 100 units away in the
   direction of view. The program dynamically changes both the
   translation and the rotation. */
static double CubeWorldXform[4][4] = {
   {1.0, 0.0, 0.0, 0.0},
   {0.0, 1.0, 0.0, 0.0},
   {0.0, 0.0, 1.0, -100.0},
   {0.0, 0.0, 0.0, 1.0} };
/* Transformation from world space into view space. Because in this
   application the view point is fixed at the origin of world space,
   looking down the Z axis in the direction of increasing Z, view space is
   identical to world space, and this is the identity matrix. */
static double WorldViewXform[4][4] = {
   {1.0, 0.0, 0.0, 0.0},
   {0.0, 1.0, 0.0, 0.0},
   {0.0, 0.0, 1.0, 0.0},
   {0.0, 0.0, 0.0, 1.0}
};
/* all vertices in the cube */
static struct Point3 CubeVerts[] = {
   {15,15,15,1},{15,15,-15,1},{15,-15,15,1},{15,-15,-15,1},
   {-15,15,15,1},{-15,15,-15,1},{-15,-15,15,1},{-15,-15,-15,1}};
/* vertices after transformation */
static struct Point3
      XformedCubeVerts[sizeof(CubeVerts)/sizeof(struct Point3)];
/* vertices after projection */
static struct Point3
      ProjectedCubeVerts[sizeof(CubeVerts)/sizeof(struct Point3)];
/* vertices in screen coordinates */
static struct Point
      ScreenCubeVerts[sizeof(CubeVerts)/sizeof(struct Point3)];
/* vertex indices for individual faces */
static int Face1[] = {1,3,2,0};
static int Face2[] = {5,7,3,1};
static int Face3[] = {4,5,1,0};
static int Face4[] = {3,7,6,2};
static int Face5[] = {5,4,6,7};
static int Face6[] = {0,2,6,4};
/* list of cube faces */
static struct Face CubeFaces[] = {{Face1,4,15},{Face2,4,14},
   {Face3,4,12},{Face4,4,11},{Face5,4,10},{Face6,4,9}};
/* master description for cube */
static struct Object Cube = {sizeof(CubeVerts)/sizeof(struct Point3),
   CubeVerts, XformedCubeVerts, ProjectedCubeVerts, ScreenCubeVerts,
   sizeof(CubeFaces)/sizeof(struct Face), CubeFaces};

void main() {
   int Done = 0, RecalcXform = 1;
   double WorkingXform[4][4];
   union REGS regset;

   /* Set up the initial transformation */
   Set320x240Mode(); /* set the screen to Mode X */
   ShowPage(PageStartOffsets[DisplayedPage = 0]);
   /* Keep transforming the cube, drawing it to the undisplayed page,
      and flipping the page to show it */
   do {
      /* Regenerate the object->view transformation and
         retransform/project if necessary */
      if (RecalcXform) {
         ConcatXforms(WorldViewXform, CubeWorldXform, WorkingXform);
         /* Transform and project all the vertices in the cube */
         XformAndProjectPoints(WorkingXform, &Cube);
         RecalcXform = 0;
      }
      CurrentPageBase =    /* select other page for drawing to */
            PageStartOffsets[NonDisplayedPage = DisplayedPage ^ 1];
      /* Clear the portion of the non-displayed page that was drawn
         to last time, then reset the erase extent */
      FillRectangleX(EraseRect[NonDisplayedPage].Left,
            EraseRect[NonDisplayedPage].Top,
            EraseRect[NonDisplayedPage].Right,
            EraseRect[NonDisplayedPage].Bottom, CurrentPageBase, 0);
      EraseRect[NonDisplayedPage].Left =
            EraseRect[NonDisplayedPage].Top = 0x7FFF;
      EraseRect[NonDisplayedPage].Right =
            EraseRect[NonDisplayedPage].Bottom = 0;
      /* Draw all visible faces of the cube */
      DrawVisibleFaces(&Cube);
      /* Flip to display the page into which we just drew */
      ShowPage(PageStartOffsets[DisplayedPage = NonDisplayedPage]);
      while (kbhit()) {
         switch (getch()) {
            case 0x1B:     /* Esc to exit */
               Done = 1; break;
            case ‘A’: case ‘a’:      /* away (-Z) */
               CubeWorldXform[2][3] -= 3.0; RecalcXform = 1; break;
            case ‘T’:      /* towards (+Z). Don’t allow to get too */
            case ‘t’:      /* close, so Z clipping isn’t needed */
               if (CubeWorldXform[2][3] < -40.0) {
                     CubeWorldXform[2][3] += 3.0;
                     RecalcXform = 1;
               }
               break;
            case ‘4’:         /* rotate clockwise around Y */
               AppendRotationY(CubeWorldXform, -ROTATION);
               RecalcXform=1; break;
            case ‘6’:         /* rotate counterclockwise around Y */
               AppendRotationY(CubeWorldXform, ROTATION);
               RecalcXform=1; break;
            case ‘8’:         /* rotate clockwise around X */
               AppendRotationX(CubeWorldXform, -ROTATION);
               RecalcXform=1; break;
            case ‘2’:         /* rotate counterclockwise around X */
               AppendRotationX(CubeWorldXform, ROTATION);
               RecalcXform=1; break;
            case 0:     /* extended code */
               switch (getch()) {
                  case 0x3B:  /* rotate counterclockwise around Z */
                     AppendRotationZ(CubeWorldXform, ROTATION);
                     RecalcXform=1; break;
                  case 0x3C:  /* rotate clockwise around Z */
                     AppendRotationZ(CubeWorldXform, -ROTATION);
                     RecalcXform=1; break;
                  case 0x4B:  /* left (-X) */
                    CubeWorldXform[0][3] -= 3.0; RecalcXform=1; break;
                  case 0x4D:  /* right (+X) */
                    CubeWorldXform[0][3] += 3.0; RecalcXform=1; break;
                  case 0x48:  /* up (+Y) */
                    CubeWorldXform[1][3] += 3.0; RecalcXform=1; break;
                  case 0x50:  /* down (-Y) */
                    CubeWorldXform[1][3] -= 3.0; RecalcXform=1; break;
                  default:
                    break;
               }
               break;
            default:       /* any other key to pause */
               getch(); break;
         }
      }
   } while (!Done);
   /* Return to text mode and exit */
   regset.x.ax = 0x0003;   /* AL = 3 selects 80x25 text mode */
   int86(0x10, &regset, &regset);
}