Laziest gouraud shader

gouraud.c

/*
Random internet code to solve system of 3 lin eqs:

float a,b,c,d,l,m,n,k,p,D,q,r,s,x,y,z;
printf("PROGRAM TO SOLVE THREE VARIABLE LINEAR SIMULTANEOUS EQUATIONS");
printf("The equations are of the form:"
"ax+by+cz+d=0"
"lx+my+nz+k=0"
"px+qy+rz+s=0");
printf("Enter the coefficients in the order a,b,c,d,l,m,n,k,p,q,r,s");
scanf("%f%f%f%f%f%f%f%f%f%f%f%f",&a,&b,&c,&d,&l,&m,&n,&k,&p,&q,&r,&s);
printf("The equations you have input are:");
printf("  %.2f*x + %.2f*y + %.2f*z + %.2f = 0",a,b,c,d);
printf("  %.2f*x + %.2f*y + %.2f*z + %.2f = 0",l,m,n,k);
printf("  %.2f*x + %.2f*y + %.2f*z + %.2f = 0",p,q,r,s);
D = (a*m*r+b*p*n+c*l*q)-(a*n*q+b*l*r+c*m*p);
x = ((b*r*k+c*m*s+d*n*q)-(b*n*s+c*q*k+d*m*r))/D;
y = ((a*n*s+c*p*k+d*l*r)-(a*r*k+c*l*s+d*n*p))/D;
z = ((a*q*k+b*l*s+d*m*p)-(a*m*s+b*p*k+d*l*q))/D;

printf("The solutions to the above three equations are :");
printf("  x = %5.2f  y = %5.2f  z = %5.2f",x,y,z);
getch();
return 0;
*/

void kdr_affinelit(BITMAP *bmp, V3D_f *v1, V3D_f *v2, V3D_f *v3)
{
	const int v1x = v1->x;
	const int v2x = v2->x;
	const int v3x = v3->x;
	
	const int v1y = v1->y;
	const int v2y = v2->y;
	const int v3y = v3->y;
	
	const int v1c = v1->c;
	const int v2c = v2->c;
	const int v3c = v3->c;
	
	#if 1
	#define KDR_AFFINELIT_LINTERP
	//Linear interpolation:
	//
	//v1x * a + v1y * b + c = v1c
	//v2x * a + v2y * b + c = v2c
	//v3x * a + v3y * b + c = v3c
	//
	//The above transformed:
	//
	//v1x * a + v1y * b + c - v1c = 0
	//v2x * a + v2y * b + c - v2c = 0
	//v3x * a + v3y * b + c - v3c = 0
	
	int D, a = 0, b = 0, c = 0;
	
	//Thus plugging the linear interpolation eqs into the solver code above:
	#define Ex a
	#define Ey b
	#define Ez c
	#define ED D
	#define Ea ((__typeof__(D))(v1x   ))
	#define Eb ((__typeof__(D))(v1y   ))
	#define Ec ((__typeof__(D))(1     ))
	#define Ed ((__typeof__(D))((-v1c)))
	#define El ((__typeof__(D))(v2x   ))
	#define Em ((__typeof__(D))(v2y   ))
	#define En ((__typeof__(D))(1     ))
	#define Ek ((__typeof__(D))((-v2c)))
	#define Ep ((__typeof__(D))(v3x   ))
	#define Eq ((__typeof__(D))(v3y   ))
	#define Er ((__typeof__(D))(1     ))
/*
Random internet code to solve system of 3 lin eqs:

float a,b,c,d,l,m,n,k,p,D,q,r,s,x,y,z;
printf("PROGRAM TO SOLVE THREE VARIABLE LINEAR SIMULTANEOUS EQUATIONS");
printf("The equations are of the form:"
"ax+by+cz+d=0"
"lx+my+nz+k=0"
"px+qy+rz+s=0");
printf("Enter the coefficients in the order a,b,c,d,l,m,n,k,p,q,r,s");
scanf("%f%f%f%f%f%f%f%f%f%f%f%f",&a,&b,&c,&d,&l,&m,&n,&k,&p,&q,&r,&s);
printf("The equations you have input are:");
printf("  %.2f*x + %.2f*y + %.2f*z + %.2f = 0",a,b,c,d);
printf("  %.2f*x + %.2f*y + %.2f*z + %.2f = 0",l,m,n,k);
printf("  %.2f*x + %.2f*y + %.2f*z + %.2f = 0",p,q,r,s);
D = (a*m*r+b*p*n+c*l*q)-(a*n*q+b*l*r+c*m*p);
x = ((b*r*k+c*m*s+d*n*q)-(b*n*s+c*q*k+d*m*r))/D;
y = ((a*n*s+c*p*k+d*l*r)-(a*r*k+c*l*s+d*n*p))/D;
z = ((a*q*k+b*l*s+d*m*p)-(a*m*s+b*p*k+d*l*q))/D;

printf("The solutions to the above three equations are :");
printf("  x = %5.2f  y = %5.2f  z = %5.2f",x,y,z);
getch();
return 0;
*/

void kdr_affinelit(BITMAP *bmp, V3D_f *v1, V3D_f *v2, V3D_f *v3)
{
	const int v1x = v1->x;
	const int v2x = v2->x;
	const int v3x = v3->x;
	
	const int v1y = v1->y;
	const int v2y = v2->y;
	const int v3y = v3->y;
	
	const int v1c = v1->c;
	const int v2c = v2->c;
	const int v3c = v3->c;
	
	#if 1
	#define KDR_AFFINELIT_LINTERP
	//Linear interpolation:
	//
	//v1x * a + v1y * b + c = v1c
	//v2x * a + v2y * b + c = v2c
	//v3x * a + v3y * b + c = v3c
	//
	//The above transformed:
	//
	//v1x * a + v1y * b + c - v1c = 0
	//v2x * a + v2y * b + c - v2c = 0
	//v3x * a + v3y * b + c - v3c = 0
	
	int D, a = 0, b = 0, c = 0;
	
	//Thus plugging the linear interpolation eqs into the solver code above:
	#define Ex a
	#define Ey b
	#define Ez c
	#define ED D
	#define Ea ((__typeof__(D))(v1x   ))
	#define Eb ((__typeof__(D))(v1y   ))
	#define Ec ((__typeof__(D))(1     ))
	#define Ed ((__typeof__(D))((-v1c)))
	#define El ((__typeof__(D))(v2x   ))
	#define Em ((__typeof__(D))(v2y   ))
	#define En ((__typeof__(D))(1     ))
	#define Ek ((__typeof__(D))((-v2c)))
	#define Ep ((__typeof__(D))(v3x   ))
	#define Eq ((__typeof__(D))(v3y   ))
	#define Er ((__typeof__(D))(1     ))
	#define Es ((__typeof__(D))((-v3c)))
	
	#define ERes 256
	
	ED = (Ea * Em * Er + Eb * Ep * En + Ec * El * Eq) - (Ea * En * Eq + Eb * El * Er + Ec * Em * Ep);
	if(ED){
		Ex = (((Eb * Er * Ek + Ec * Em * Es + Ed * En * Eq) - (Eb * En * Es + Ec * Eq * Ek + Ed * Em * Er)) * ERes) / ED;
		Ey = (((Ea * En * Es + Ec * Ep * Ek + Ed * El * Er) - (Ea * Er * Ek + Ec * El * Es + Ed * En * Ep)) * ERes) / ED;
		//Constant term needs no fixed point factor
		Ez = (((Ea * Eq * Ek + Eb * El * Es + Ed * Em * Ep) - (Ea * Em * Es + Eb * Ep * Ek + Ed * El * Eq))       ) / ED;
	}
	
	#undef Ex
	#undef Ey
	#undef Ez
	#undef Ea
	#undef Eb
	#undef Ec
	#undef Ed
	#undef El
	#undef Em
	#undef En
	#undef Ek
	#undef Ep
	#undef Eq
	#undef Er
	#undef Es
	#undef ED
	
	#endif
	
	const uint16_t *max = ktaz_ptr.y;
	for(ktaz_ptr = ktaz_p0; ktaz_ptr.y < max; ktaz_ptr.y++, ktaz_ptr.n++){
		for(; *ktaz_ptr.n; *ktaz_ptr.n -= 1, ktaz_ptr.l++, ktaz_ptr.x++){
			for(; *ktaz_ptr.l; *ktaz_ptr.l -= 1){
				const int x = *ktaz_ptr.x + *ktaz_ptr.l - 1;
				const int y = *ktaz_ptr.y;
				_putpixel(bmp, x, y,
					#ifdef KDR_AFFINELIT_LINTERP
					MIN(MAX(0, (x * a + y * b) / ERes + c), 255)
					#undef ERes
					#undef KDR_AFFINELIT_LINTERP
					#else
					(v3c + v2c + v1c) / 3
					#endif
				);
			}
		}
	}
}