Sand Dollar in OpenGL/C++

//
//  main.cpp
//  SandDollar
//
//  Created by Zevan Rosser on 1/22/11.
//
 
#include <iostream>
#include <GLUT/glut.h>
#include <OpenGL/OpenGL.h>
 
#define _USE_MATH_DEFINES
#include <cmath>
 
#define P_WIDTH  100
#define P_HEIGHT  150
#define NUM_POINTS  P_WIDTH * P_HEIGHT
 
// using namespace std; // for debugging with cout
 
typedef struct {
	float r, g, b, a;
} Color; 
 
 
typedef struct {
	float x;
	float y;
} Pnt;
 
int mouseX = 0;
int mouseY = 0;
int width, height;
 
Pnt points[NUM_POINTS];
Pnt easePoints[NUM_POINTS];
Color colors[NUM_POINTS];
 
void setupPoints(){
	int inc = 0;
 
	int hw = width / 2;
	int hh = height / 2;
	const float STEP = 2.399976;
	const float toRads = M_PI / 180.0;
 
	for (float i = 0; i < P_WIDTH; i++){
		for (float j = 0; j < P_HEIGHT; j++){
			float t = j * STEP;
			float r = (i + 5.0) * 4.0;
			float xp = hw + r * cos(t * toRads);
			float yp = hh + r * sin(t * toRads);
			Pnt p = {xp, yp};
			Pnt pe = {xp, yp};
			points[inc] = p;
			easePoints[inc] = pe;
			Color col = {1.0, 1.0, 1.0, 0.1};
 
			colors[inc] = col;
			inc++;
		}
	}
 
	glEnableClientState(GL_VERTEX_ARRAY);
	glEnableClientState(GL_COLOR_ARRAY); 
	glVertexPointer(2, GL_FLOAT, 0, easePoints);
	glColorPointer(4, GL_FLOAT, 0, colors);
}
 
inline float angle(float x0, float y0, float x1, float y1){
	float dx = x0 - x1;
	float dy = y0 - y1;
	return atan2(dy, dx);
}
 
inline float dist(float x0, float y0, float x1, float y1){
	float dx = x0 - x1;
	float dy = y0 - y1;
	return sqrt(dx * dx + dy * dy);
}
 
Pnt repel(float xp, float yp){
	float d = dist(xp, yp, mouseX, mouseY);
	if (d < 400.0){
		float ang = angle(xp, yp, mouseX, mouseY);
		xp = mouseX + 500 * cos(ang);
		yp = mouseY + 500 * sin(ang);
	}
	Pnt pnt = {xp, yp};
	return pnt;
}
 
void init(){
	glPointSize(20.0);
}
 
void render() {
	glClear(GL_COLOR_BUFFER_BIT);
 
	Pnt p;
	for (int i = 0; i<NUM_POINTS; i++){
		p = repel(points[i].x, points[i].y);
		easePoints[i].x += (p.x - easePoints[i].x) * 0.02;
		easePoints[i].y += (p.y - easePoints[i].y) * 0.02;
	}
 
	glDrawArrays(GL_POINTS, 0, NUM_POINTS);
 
	glutSwapBuffers();
}
 
bool firstResize = true;
void resize(int w, int h) {
	width = w;
	height = h;
	if (firstResize){
		setupPoints();
	}
	glViewport(0, 0, w, h);
	glMatrixMode(GL_PROJECTION);  
	glLoadIdentity();            
	glOrtho(0, w, 0, h, -1, 1);   
	glScalef(1, -1, 1);         
	glTranslatef(0, -h, 0);
}
 
void idle() {
	glutPostRedisplay();
}
 
void mouse(int x, int y){
	mouseX = x;
	mouseY = y;
}
 
int main(int argc, char** argv){
 
	glutInit(&argc, argv);
 
	glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE);
 
	glutInitWindowSize(640, 480);
	glutCreateWindow("Sand Dollar");
	glutFullScreen();
 
	glutPassiveMotionFunc(mouse);
	glutDisplayFunc(render);
	glutReshapeFunc(resize);
	glutIdleFunc(idle);
 
	glEnable (GL_BLEND);	
	glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
	glDisable(GL_DEPTH_TEST);
 
	glEnable (GL_POINT_SMOOTH);
	glHint (GL_POINT_SMOOTH_HINT, GL_NICEST);
 
	// VBL synching
	GLint sync = 1;
	CGLSetParameter(CGLGetCurrentContext(), kCGLCPSwapInterval, &sync);
 
	init();
	glutMainLoop();
 
	return EXIT_SUCCESS;
}