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Sourcecode: acm4 version File versions  Download package

VDepthCue.c

#include "Vlib.h"

void
VSetVisibility(d)
double      d;
{
      int   i;
      double      k;

      _VDefaultWorkContext->visibility = d;
      if (_VDefaultWorkContext->visTable) {
            free ((char *) _VDefaultWorkContext->visTable);
      }

      _VDefaultWorkContext->visTable = (double *) Vmalloc (sizeof(double) *
            _VDefaultWorkContext->depthCueSteps);

      k = log (1.0 / (double) _VDefaultWorkContext->depthCueSteps) /
            _VDefaultWorkContext->visibility;

#ifdef DEBUG
      fprintf (stderr, "k = %lg\n", k);
#endif
      
      for (i=0; i<_VDefaultWorkContext->depthCueSteps-1; ++i) {
          _VDefaultWorkContext->visTable[i] =
            log (1.0 - (double)(i+1) /
            (double)_VDefaultWorkContext->depthCueSteps) / k;
#ifdef DEBUG
            fprintf (stderr, "next threshold is %lg units\n",
                  _VDefaultWorkContext->visTable[i] );
#endif
      }
}

int
VComputePolygonColor (v, poly)
Viewport *v;
VPolygon *poly;
{
      VColor      *c;
      VPoint      *p;
      int   i;
      double      d;

/*
 *  First, are we seeing the front or the back of this polygon?
 */
 
      if (poly->flags & PolyUseBackColor) {
            c = poly->backColor;
      }
      else {
            c = poly->color;
      }

/*
 *  If depth queueing isn't turned on, or this color is not a depth-cueued
 *  color, then simply return the color index.
 */
 
      if ((v->flags & VPDepthCueing) == 0 || 
            (c->flags & ColorEnableDepthCueing) == 0) {
            return v->pixel[c->cIndex];
      }

/*
 *  Okay, it is a depth cueued color.  Check this polygon's distance against
 *  the different cutoff points for the current world visibility value.  If the
 *  distance is greater than any of the cutoff values, then render the object
 *  as a pure "haze" color.
 */

      else {
            if ((i = poly->assignedDepth) > -1) {
                return v->pixel[(i<_VDefaultWorkContext->depthCueSteps-1) ?
                  c->cIndex + i :
                  _VDefaultWorkContext->depthCueColor->cIndex ];
            }
            p = &poly->vertex[0];
            d = sqrt(p->x * p->x + p->y * p->y + p->z * p->z);
            for (i=0; i<_VDefaultWorkContext->depthCueSteps-1; ++i) {
                  if (d < _VDefaultWorkContext->visTable[i]) {
                        return v->pixel[c->cIndex + i];
                  }
            }
            return v->pixel[_VDefaultWorkContext->depthCueColor->cIndex];
      }
}


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