LISTING 52.6 L52-6.C

/* Rotates and moves a polygon-based object around the three axes.
   Movement is implemented only along the Z axis currently. */

#include “polygon.h”

void RotateAndMovePObject(PObject * ObjectToMove)
{
   if (--ObjectToMove->RDelayCount == 0) {   /* rotate */
      ObjectToMove->RDelayCount = ObjectToMove->RDelayCountBase;
      if (ObjectToMove->Rotate.RotateX != 0.0)
         AppendRotationX(ObjectToMove->XformToWorld,
               ObjectToMove->Rotate.RotateX);
      if (ObjectToMove->Rotate.RotateY != 0.0)
         AppendRotationY(ObjectToMove->XformToWorld,
               ObjectToMove->Rotate.RotateY);
      if (ObjectToMove->Rotate.RotateZ != 0.0)
         AppendRotationZ(ObjectToMove->XformToWorld,
               ObjectToMove->Rotate.RotateZ);
      ObjectToMove->RecalcXform = 1;
   }
   /* Move in Z, checking for bouncing and stopping */
   if (--ObjectToMove->MDelayCount == 0) {
      ObjectToMove->MDelayCount = ObjectToMove->MDelayCountBase;
      ObjectToMove->XformToWorld[2][3] += ObjectToMove->Move.MoveZ;
      if (ObjectToMove->XformToWorld[2][3]>ObjectToMove->Move.MaxZ)
         ObjectToMove->Move.MoveZ = 0; /* stop if close enough */
      ObjectToMove->RecalcXform = 1;
   }
}

LISTING 52.7 L52-7.C

/* Draws all visible faces in specified polygon-based object. Object must have
   previously been transformed and projected, so that ScreenVertexList array is
   filled in. */

#include “polygon.h”

void DrawPObject(PObject * ObjectToXform)
{
   int i, j, NumFaces = ObjectToXform->NumFaces, NumVertices;
   int * VertNumsPtr;
   Face * FacePtr = ObjectToXform->FaceList;
   Point * ScreenPoints = ObjectToXform->ScreenVertexList;
   long v1, v2, w1, w2;
   Point Vertices[MAX_POLY_LENGTH];
   PointListHeader Polygon;

   /* Draw each visible face (polygon) of the object in turn */
   for (i=0; i<NumFaces; i++, FacePtr++) {
      NumVertices = FacePtr->NumVerts;
      /* Copy over the face's vertices from the vertex list */
      for (j=0, VertNumsPtr=FacePtr->VertNums; j<NumVertices; j++)
         Vertices[j] = ScreenPoints[*VertNumsPtr++];
      /* Draw only if outside face showing (if the normal to the
         polygon points toward viewer; that is, has a positive Z component) */
      v1 = Vertices[1].X - Vertices[0].X;
      w1 = Vertices[NumVertices-1].X - Vertices[0].X;
      v2 = Vertices[1].Y - Vertices[0].Y;
      w2 = Vertices[NumVertices-1].Y - Vertices[0].Y;
      if ((v1*w2 - v2*w1) > 0) {
         /* It is facing the screen, so draw */
         /* Appropriately adjust the extent of the rectangle used to
            erase this object later */
         for (j=0; j<NumVertices; j++) {
            if (Vertices[j].X >
                  ObjectToXform->EraseRect[NonDisplayedPage].Right)
               if (Vertices[j].X < SCREEN_WIDTH)
                  ObjectToXform->EraseRect[NonDisplayedPage].Right =
                        Vertices[j].X;
               else ObjectToXform->EraseRect[NonDisplayedPage].Right =
                     SCREEN_WIDTH;
            if (Vertices[j].Y >
                  ObjectToXform->EraseRect[NonDisplayedPage].Bottom)
               if (Vertices[j].Y < SCREEN_HEIGHT)
                  ObjectToXform->EraseRect[NonDisplayedPage].Bottom =
                        Vertices[j].Y;
               else ObjectToXform->EraseRect[NonDisplayedPage].Bottom=
                     SCREEN_HEIGHT;
            if (Vertices[j].X <
                  ObjectToXform->EraseRect[NonDisplayedPage].Left)
               if (Vertices[j].X > 0)
                  ObjectToXform->EraseRect[NonDisplayedPage].Left =
                        Vertices[j].X;
               else ObjectToXform->EraseRect[NonDisplayedPage].Left=0;
            if (Vertices[j].Y <
                  ObjectToXform->EraseRect[NonDisplayedPage].Top)
               if (Vertices[j].Y > 0)
                  ObjectToXform->EraseRect[NonDisplayedPage].Top =
                        Vertices[j].Y;
               else ObjectToXform->EraseRect[NonDisplayedPage].Top=0;
         }
         /* Draw the polygon */
         DRAW_POLYGON(Vertices, NumVertices, FacePtr->Color, 0, 0);
      }
   }
}