HPAVC/HPAVC CD-ROM.iso/PHONG.ZIP/SPHERE.C

C/C++ Source or Header | 1995-10-15 | 5KB | 195 lines

// Phong Shading Demo. By Keith Harrison (CIS:100431,1675). 15th Oct. 1995
// Shades 20 spheres with differing values of Kd (diffuse)
// and Ks (specular) properties.
// Program uses single equation shading, evaluating only the red component.
// Uses Watcom's graphics library (graph.h)

// Phong's equation for Intensity:
// I = IaKa + Ii[Kd(L.N) + Ks(N.H)ⁿ] / (r + K)

// Developed with Watcom V10.0a from the MS Windows version
// (the Windows version plotted 24bit colour values).

// Based on information in 'Fundamentals of Three-Dimensional Computer
// Graphics' by Alan Watt, ISBN 0 201 15442 0.

#include <conio.h>
#include <graph.h>
#include <math.h>

//Function prototypes.
void setpalette(void);
void plotpixel(short x, short y, short colour);

void ShadeSphere(float Kd, float Ks,
                 short SpecIndex, short Xcentre, short Ycentre, short radius);

void CalculateLNandNnH( short x,  short y, short z, short SpecIndex,
                        float xn, float yn, float zn,
                        float *LdotN, float *dist, float *NnH);

//Ambient light intensity (0 to 1)
const float IaKa = 0.2;

//Vector H is the unit normal to the hypothetical surface oriented
//halfway between the light direction vector (L) and the viewing vector (V).
const float Hx = 0.326058, Hy = 0.325058, Hz = 0.888074;

//Intensity of light source.
const short Ilight = 140;
//Light source distance factor.
const float K = 70;
//Light source position.
const float dx = 110, dy = 110, dz = 110;
//Light source normal.
const float Lx = 0.57735, Ly = 0.57735, Lz = 0.57735;

long palette[256];

void setpalette(void)
{
  short i;

  //The VGA can only handle 64 different shades of red.
  for (i=0; i<64; i++)
    palette[i] = (long)i;

  _remapallpalette( &palette);
};



void plotpixel(short x, short y, short colour)
{
  _setcolor(colour);
  _setpixel(x, y);
};



void CalculateLNandNnH( short x,  short y, short z, short SpecIndex,
                        float xn, float yn, float zn,
                        float *LdotN, float *dist, float *NnH)
{
  float NH;

  *LdotN = xn*Lx + yn*Ly + zn*Lz;

  if (LdotN <= 0)
    LdotN = 0;
  else {
    *dist = sqrt((dx - x)*(dx - x) + (dy - y)*(dy - y) + (dz - z)*(dz - z));
    NH = Hx*xn + Hy*yn + Hz*zn;
    *NnH = exp(SpecIndex*log(NH));
  }
};



void ShadeSphere(float Kd, float Ks,
                 short SpecIndex, short Xcentre, short Ycentre, short radius)
{
  short Ir, Igb; // Ir = intensity of Red, Igb = intensity of green/blue.
  int x, y, z; // Coordinates of point on sphere surface.
  float rsquare, xsquare, ysquare, zsquare, denom, xn, yn, zn, LdotN, NnH,
        dist, distfactor, ambientterm, diffuseterm, specularterm;

  rsquare = radius * radius;

  for (y = -radius; y<radius; y++) {
    ysquare = y * y;
    for (x = -radius; x<radius; x++) {
      xsquare = x * x;
      if ( (xsquare + ysquare) <= rsquare) {
        z = sqrt(rsquare - xsquare - ysquare);
        zsquare = z * z;
        denom = sqrt(xsquare + ysquare + zsquare);
        // xn, yn, and zn are unit normals from the sphere surface.
        xn = x / denom;
        yn = y / denom;
        zn = z / denom;
        CalculateLNandNnH(x, y, z, SpecIndex, xn, yn, zn, &LdotN, &dist, &NnH);
        ambientterm = IaKa;
        if (LdotN <= 0) {
          //Point is not illuminated by light source.
          //Use only ambient component.
          Ir = 64 * ambientterm;
          Igb = 0;
        }
        else {
          distfactor = Ilight / (dist + K);
          diffuseterm = distfactor * Kd * LdotN;
          specularterm = distfactor * Ks * NnH;
          Ir = 64 * (ambientterm + diffuseterm + specularterm);
          Igb = 64 * specularterm;
        };
        plotpixel(Xcentre + x, Ycentre + y, Ir);
      }
    }
  }

};



int main(int argc, char *argv[])
{
  short SpecIndex, i, j, Xpos, Ypos;
  float Kd, Ks;

  int videomode;

  if (argc != 2) {
    printf("\nPhong Shaded Spheres.\n");
    printf("By Keith Harrison.\n\n");
    printf("Usage: sphere <video_mode>\n");
    printf("Video modes: 320  =  320 x 200 x 256 colour (VGA)\n");
    printf("             640  =  640 x 480 x 256 colour (SVGA)\n");
    printf("             800  =  800 x 600 x 256 colour (SVGA)\n");
    printf("             1024 = 1024 x 768 x 256 colour (SVGA)\n\n");
    return 1;
  };

  videomode = atoi(argv[1]);

  switch (videomode) {
    case 320:  _setvideomode( _MRES256COLOR ); break;
    case 640:  _setvideomode( _VRES256COLOR ); break;
    case 800:  _setvideomode( _SVRES256COLOR ); break;
    case 1024: _setvideomode( _XRES256COLOR ); break;
    default:
      printf("\nIncorrect command line option.\n");
      printf("Defaulting to 640 x 480 x 256 colours\n");
      printf("Type 'sphere' to see options\n");
      printf("Press any key to continue.\n");
      getch();
      _setvideomode( _VRES256COLOR ); break;
  };

  setpalette();

  SpecIndex = 9;
  Ypos = 50;

  for (i=0; i<4; i++) {
    Xpos = 50;
    Kd = 0;
    Ks = 1;
    for(j=0; j<5; j++) {
      ShadeSphere(Kd, Ks, SpecIndex, Xpos, Ypos, 50);
      Kd += 0.25;
      Ks -= 0.25;
      Xpos += 110;
    };
    Ypos += 110;
    SpecIndex = SpecIndex * 2;
  };

  getch();
  _setvideomode( _DEFAULTMODE );

  return 0;

}