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heart3d.c 2.01 KB
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wamwamja authored 2017-10-31 02:15 . 新建 heart3d.c
#include <stdio.h>
#include <math.h>
double f(double x, double y, double z);
double fx(double x, double y, double z);
double fy(double x, double y, double z);
double fz(double x, double y, double z);
double compute_y(double x, double z);
int main(int argc, char const *argv[])
{
int width = 512, height = 512;
FILE *fp = fopen("heart3d.ppm","w");
fprintf(fp, "P3 %d %d 255\n", width, height);
double x, y, z, nx, ny, nz, a;
// 光源方向(入射光方向)
double lx = 1, ly = 1, lz = -1;
double L = sqrt(lx*lx+ly*ly+lz*lz);
lx = lx / L;
ly = ly / L;
lz = lz / L;
for (int h=0; h<height; h++)
{
// z \in [-1.5, 1.5]
z = - h*3.0/height + 1.5;
for (int w=0; w<width; w++)
{
// z \in [-1.5, 1.5]
x = w*3.0/width - 1.5;
int r = 0;
// 点在心形图内
if (f(x,0,z) < 0)
{
// 计算y
y = compute_y(x,z);
// 计算梯度(法向量)
nx = fx(x,y,z);
ny = fy(x,y,z);
nz = fz(x,y,z);
// light source (1,1,-0.5)
a = (lx*nx + ly*ny + lz*nz)/sqrt(nx*nx+ny*ny+nz*nz);
// 根据入射光与法线夹角余弦值计算光强
r = (int) ((0.5 * a + 0.5)*255);
}
fprintf(fp, "%d 0 0 ", r);
}
fprintf(fp,"\n");
}
return 0;
}
double f(double x, double y, double z){
double a = x*x + 9.0f/4.0f*y*y + z*z - 1;
return a*a*a - x*x*z*z*z - 9.0f/80.0f*y*y*z*z*z;
}
double fx(double x, double y, double z){
double dx = 1e-8;
return (f(x+dx,y,z) - f(x-dx,y,z)) / (2*dx);
}
double fy(double x, double y, double z){
double dy = 1e-8;
return (f(x,y+dy,z) - f(x,y-dy,z)) / (2*dy);
}
double fz(double x, double y, double z){
double dz = 1e-8;
return (f(x,y,z+dz) - f(x,y,z-dz)) / (2*dz);
}
double compute_y(double x, double z){
double z_min = 0.0, z_max = 1.5;
double eps = 1e-6, r = 1.0, y;
while(r>eps){
y = (z_min + z_max) / 2.0;
if (f(x,y,z) == 0)
return y;
if (f(x,y,z) > 0)
z_max = y;
else
z_min = y;
r = z_max - z_min;
}
return 0.5*(z_max + z_min);
}

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