/* Transforms all vertices in the specified object into view space,
   then perspective projects them to screen space and maps them to
   screen coordinates, storing the results in the object. */
#include <math.h>
#include "polygon.h"

void XformAndProjectPoints(double Xform[4][4],
   struct Object * ObjectToXform)
{
   int i, NumPoints = ObjectToXform->NumVerts;
   struct Point3 * Points = ObjectToXform->VertexList;
   struct Point3 * XformedPoints = ObjectToXform->XformedVertexList;
   struct Point3 * ProjectedPoints =
         ObjectToXform->ProjectedVertexList;
   struct Point * ScreenPoints = ObjectToXform->ScreenVertexList;

   for (i=0; i<NumPoints; i++, Points++, XformedPoints++,
         ProjectedPoints++, ScreenPoints++) {
      /* Transform to view space */
      XformVec(Xform, (double *)Points, (double *)XformedPoints);
      /* Perspective-project to screen space */
      ProjectedPoints->X = XformedPoints->X / XformedPoints->Z *
            PROJECTION_RATIO * (SCREEN_WIDTH / 2.0);
      ProjectedPoints->Y = XformedPoints->Y / XformedPoints->Z *
            PROJECTION_RATIO * (SCREEN_WIDTH / 2.0);
      ProjectedPoints->Z = XformedPoints->Z;
      /* Convert to screen coordinates. The Y coord is negated to
         flip from increasing Y being up to increasing Y being down,
         as expected by the polygon filler. Add in half the screen
         width and height to center on the screen */
      ScreenPoints->X = ((int) floor(ProjectedPoints->X + 0.5)) +
               SCREEN_WIDTH/2;
      ScreenPoints->Y = (-((int) floor(ProjectedPoints->Y + 0.5))) +
               SCREEN_HEIGHT/2;
   }
}