gl_spharmonics.h
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#ifndef STIM_GL_SPHARMONICS_H
#define STIM_GL_SPHARMONICS_H
#include <GL/gl.h>
#include <stim/gl/error.h>
#include <stim/visualization/colormap.h>
#include <stim/math/spharmonics.h>
namespace stim{
template <typename T>
class gl_spharmonics : public spharmonics<T>{
protected:
using spharmonics<T>::C;
using spharmonics<T>::SH;
T* func; //stores the raw function data (samples at each point)
GLuint color_tex; //texture map that acts as a colormap for the spherical function
unsigned int N; //resolution of the spherical grid
void gen_function(){
//initialize the function to zero
memset(func, 0, sizeof(double) * N * N);
double theta, phi;
double result;
int l, m;
l = m = 0;
//for each coefficient
for(unsigned int c = 0; c < C.size(); c++){
//iterate through the entire 2D grid representing the function
for(unsigned int xi = 0; xi < N; xi++){
for(unsigned int yi = 0; yi < N; yi++){
//get the spherical coordinates for each grid point
theta = (2 * PI) * ((double)xi / (N-1));
phi = PI * ((double)yi / (N-1));
//sum the contribution of the current spherical harmonic based on the coefficient
result = C[c] * SH(l, m, theta, phi);
//store the result in a 2D array (which will later be used as a texture map)
func[yi * N + xi] += result;
}
}
//keep track of m and l here
m++; //increment m
//if we're in a new tier, increment l and set m = -l
if(m > l){
l++;
m = -l;
}
}
}
void gl_prep_draw(){
//enable depth testing
//this has to be used instead of culling because the sphere can have negative values
glEnable(GL_DEPTH_TEST);
glDepthMask(GL_TRUE);
glEnable(GL_TEXTURE_2D); //enable 2D texture mapping
}
//draw a texture mapped sphere representing the function surface
void gl_draw_sphere() {
//bind the 2D texture representing the color map
glBindTexture(GL_TEXTURE_2D, color_tex);
//Draw the Sphere
int i, j;
for(i = 1; i <= N-1; i++) {
double phi0 = PI * ((double) (i - 1) / (N-1));
double phi1 = PI * ((double) i / (N-1));
glBegin(GL_QUAD_STRIP);
for(j = 0; j <= N; j++) {
//calculate the indices into the function array
int phi0_i = i-1;
int phi1_i = i;
int theta_i = j;
if(theta_i == N)
theta_i = 0;
double v0 = func[phi0_i * N + theta_i];
double v1 = func[phi1_i * N + theta_i];
v0 = fabs(v0);
v1 = fabs(v1);
double theta = 2 * PI * (double) (j - 1) / N;
double x0 = v0 * cos(theta) * sin(phi0);
double y0 = v0 * sin(theta) * sin(phi0);
double z0 = v0 * cos(phi0);
double x1 = v1 * cos(theta) * sin(phi1);
double y1 = v1 * sin(theta) * sin(phi1);
double z1 = v1 * cos(phi1);
glTexCoord2f(theta / (2 * PI), phi0 / PI);
glVertex3f(x0, y0, z0);
glTexCoord2f(theta / (2 * PI), phi1 / PI);
glVertex3f(x1, y1, z1);
}
glEnd();
}
}
void gl_init(unsigned int n){
//set the sphere resolution
N = n;
//allocate space for the color map
unsigned int bytes = N * N * sizeof(unsigned char) * 3;
unsigned char* color_image;
color_image = (unsigned char*) malloc(bytes);
//allocate space for the function
func = (double*) malloc(N * N * sizeof(double));
//generate a functional representation that will be used for the texture map and vertices
gen_function();
//generate a colormap from the function
stim::cpu2cpu<double>(func, color_image, N*N, stim::cmBrewer);
//prep everything for drawing
gl_prep_draw();
//generate an OpenGL texture map in the current context
glGenTextures(1, &color_tex);
//bind the texture
glBindTexture(GL_TEXTURE_2D, color_tex);
//copy the color data from the buffer to the GPU
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, N, N, 0, GL_RGB, GL_UNSIGNED_BYTE, color_image);
//initialize all of the texture parameters
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
//free the buffer
free(color_image);
}
public:
gl_spharmonics<T>() {
}
gl_spharmonics<T>(const spharmonics<T> copy) : gl_spharmonics<T>() {
C = copy.C;
}
gl_spharmonics<T>& operator=(const spharmonics<T> rhs) {
gl_spharmonics<T> result(rhs.C.size());
result.C = spharmonics<T>::rhs.C;
return result;
}
void glRender(){
//set all OpenGL parameters required for drawing
gl_prep_draw();
//draw the sphere
gl_draw_sphere();
}
void glInit(unsigned int n = 256){
gl_init(n);
gen_function();
}
//overload arithmetic operations
gl_spharmonics<T> operator*(T rhs) const {
gl_spharmonics<T> result(C.size()); //create a new sph erical harmonics object
for (size_t c = 0; c < C.size(); c++) //for each coefficient
result.C[c] = C[c] * rhs; //calculat e the factor and store the result in the new spharmonics object
return result;
}
gl_spharmonics<T> operator+(gl_spharmonics<T> rhs) {
size_t low = std::min(C.size(), rhs.C.size()); //store th e number of coefficients in the lowest object
size_t high = std::max(C.size(), rhs.C.size()); //store th e number of coefficients in the result
bool rhs_lowest = false; //true if rhs has the lowest number of coefficients
if (rhs.C.size() < C.size()) rhs_lowest = true; //if rhs has a low er number of coefficients, set the flag
gl_spharmonics<T> result(high); //create a new object
size_t c;
for (c = 0; c < low; c++) //perform the first batch of additions
result.C[c] = C[c] + rhs.C[c]; // perform the addition
for (c = low; c < high; c++) {
if (rhs_lowest)
result.C[c] = C[c];
else
result.C[c] = rhs.C[c];
}
return result;
}
gl_spharmonics<T> operator-(gl_spharmonics<T> rhs) {
return (*this) + (rhs * (T)(-1));
}
}; //end gl_spharmonics
}; //end namespace stim
#endif