Xcode-iOS/Demos/src/fireworks.c - third_party/sdl - Git at Google

 /*
  *  fireworks.c
  *  written by Holmes Futrell
  *  use however you want
  */

 #include "SDL.h"
 #include "SDL_opengles.h"
 #include "common.h"
 #include <math.h>
 #include <time.h>

 #define ACCEL 0.0001f           /* acceleration due to gravity, units in pixels per millesecond squared */
 #define WIND_RESISTANCE 0.00005f        /* acceleration per unit velocity due to wind resistance */
 #define MAX_PARTICLES 2000      /* maximum number of particles displayed at once */

 static GLuint particleTextureID;        /* OpenGL particle texture id */
 static SDL_bool pointSizeExtensionSupported;    /* is GL_OES_point_size_array supported ? */
 static float pointSizeScale;
 /*
     used to describe what type of particle a given struct particle is.
     emitter - this particle flies up, shooting off trail particles, then finally explodes into dust particles.
     trail   - shoots off, following emitter particle
     dust    - radiates outwards from emitter explosion
 */
 enum particleType
 {
     emitter = 0,
     trail,
     dust
 };
 /*
     struct particle is used to describe each particle displayed on screen
 */
 struct particle
 {
     GLfloat x;                  /* x position of particle */
     GLfloat y;                  /* y position of particle */
     GLubyte color[4];           /* rgba color of particle */
     GLfloat size;               /* size of particle in pixels */
     GLfloat xvel;               /* x velocity of particle in pixels per milesecond */
     GLfloat yvel;               /* y velocity of particle in pixels per millescond */
     int isActive;               /* if not active, then particle is overwritten */
     enum particleType type;     /* see enum particleType */
 } particles[MAX_PARTICLES];     /* this array holds all our particles */

 static int num_active_particles;        /* how many members of the particle array are actually being drawn / animated? */
 static int screen_w, screen_h;

 /* function declarations */
 void spawnTrailFromEmitter(struct particle *emitter);
 void spawnEmitterParticle(GLfloat x, GLfloat y);
 void explodeEmitter(struct particle *emitter);
 void initializeParticles(void);
 void initializeTexture();
 int nextPowerOfTwo(int x);
 void drawParticles();
 void stepParticles(double deltaTime);

 /*  helper function (used in texture loading)
     returns next power of two greater than or equal to x
 */
 int
 nextPowerOfTwo(int x)
 {
     int val = 1;
     while (val < x) {
         val *= 2;
     }
     return val;
 }

 /*
     steps each active particle by timestep deltaTime
 */
 void
 stepParticles(double deltaTime)
 {
     float deltaMilliseconds = deltaTime * 1000;
     int i;
     struct particle *slot = particles;
     struct particle *curr = particles;
     for (i = 0; i < num_active_particles; i++) {
         /* is the particle actually active, or is it marked for deletion? */
         if (curr->isActive) {
             /* is the particle off the screen? */
             if (curr->y > screen_h)
                 curr->isActive = 0;
             else if (curr->y < 0)
                 curr->isActive = 0;
             if (curr->x > screen_w)
                 curr->isActive = 0;
             else if (curr->x < 0)
                 curr->isActive = 0;

             /* step velocity, then step position */
             curr->yvel += ACCEL * deltaMilliseconds;
             curr->xvel += 0.0f;
             curr->y += curr->yvel * deltaMilliseconds;
             curr->x += curr->xvel * deltaMilliseconds;

             /* particle behavior */
             if (curr->type == emitter) {
                 /* if we're an emitter, spawn a trail */
                 spawnTrailFromEmitter(curr);
                 /* if we've reached our peak, explode */
                 if (curr->yvel > 0.0) {
                     explodeEmitter(curr);
                 }
             } else {
                 float speed =
                     sqrt(curr->xvel * curr->xvel + curr->yvel * curr->yvel);
                 /*      if wind resistance is not powerful enough to stop us completely,
                    then apply winde resistance, otherwise just stop us completely */
                 if (WIND_RESISTANCE * deltaMilliseconds < speed) {
                     float normx = curr->xvel / speed;
                     float normy = curr->yvel / speed;
                     curr->xvel -=
                         normx * WIND_RESISTANCE * deltaMilliseconds;
                     curr->yvel -=
                         normy * WIND_RESISTANCE * deltaMilliseconds;
                 } else {
                     curr->xvel = curr->yvel = 0;        /* stop particle */
                 }

                 if (curr->color[3] <= deltaMilliseconds * 0.1275f) {
                     /* if this next step will cause us to fade out completely
                        then just mark for deletion */
                     curr->isActive = 0;
                 } else {
                     /* otherwise, let's fade a bit more */
                     curr->color[3] -= deltaMilliseconds * 0.1275f;
                 }

                 /* if we're a dust particle, shrink our size */
                 if (curr->type == dust)
                     curr->size -= deltaMilliseconds * 0.010f;

             }

             /* if we're still active, pack ourselves in the array next
                to the last active guy (pack the array tightly) */
             if (curr->isActive)
                 *(slot++) = *curr;
         }                       /* endif (curr->isActive) */
         curr++;
     }
     /* the number of active particles is computed as the difference between
        old number of active particles, where slot points, and the
        new size of the array, where particles points */
     num_active_particles = (int) (slot - particles);
 }

 /*
     This draws all the particles shown on screen
 */
 void
 drawParticles()
 {

     /* draw the background */
     glClear(GL_COLOR_BUFFER_BIT);

     /* set up the position and color pointers */
     glVertexPointer(2, GL_FLOAT, sizeof(struct particle), particles);
     glColorPointer(4, GL_UNSIGNED_BYTE, sizeof(struct particle),
                    particles[0].color);

     if (pointSizeExtensionSupported) {
         /* pass in our array of point sizes */
         glPointSizePointerOES(GL_FLOAT, sizeof(struct particle),
                               &(particles[0].size));
     }

     /* draw our particles! */
     glDrawArrays(GL_POINTS, 0, num_active_particles);

 }

 /*
     This causes an emitter to explode in a circular bloom of dust particles
 */
 void
 explodeEmitter(struct particle *emitter)
 {
     /* first off, we're done with this particle, so turn active off */
     emitter->isActive = 0;
     int i;
     for (i = 0; i < 200; i++) {

         if (num_active_particles >= MAX_PARTICLES)
             return;

         /* come up with a random angle and speed for new particle */
         float theta = randomFloat(0, 2.0f * 3.141592);
         float exponent = 3.0f;
         float speed = randomFloat(0.00, powf(0.17, exponent));
         speed = powf(speed, 1.0f / exponent);

         /* select the particle at the end of our array */
         struct particle *p = &particles[num_active_particles];

         /* set the particles properties */
         p->xvel = speed * cos(theta);
         p->yvel = speed * sin(theta);
         p->x = emitter->x + emitter->xvel;
         p->y = emitter->y + emitter->yvel;
         p->isActive = 1;
         p->type = dust;
         p->size = 15 * pointSizeScale;
         /* inherit emitter's color */
         p->color[0] = emitter->color[0];
         p->color[1] = emitter->color[1];
         p->color[2] = emitter->color[2];
         p->color[3] = 255;
         /* our array has expanded at the end */
         num_active_particles++;
     }

 }

 /*
     This spawns a trail particle from an emitter
 */
 void
 spawnTrailFromEmitter(struct particle *emitter)
 {

     if (num_active_particles >= MAX_PARTICLES)
         return;

     /* select the particle at the slot at the end of our array */
     struct particle *p = &particles[num_active_particles];

     /* set position and velocity to roughly that of the emitter */
     p->x = emitter->x + randomFloat(-3.0, 3.0);
     p->y = emitter->y + emitter->size / 2.0f;
     p->xvel = emitter->xvel + randomFloat(-0.005, 0.005);
     p->yvel = emitter->yvel + 0.1;

     /* set the color to a random-ish orangy type color */
     p->color[0] = (0.8f + randomFloat(-0.1, 0.0)) * 255;
     p->color[1] = (0.4f + randomFloat(-0.1, 0.1)) * 255;
     p->color[2] = (0.0f + randomFloat(0.0, 0.2)) * 255;
     p->color[3] = (0.7f) * 255;

     /* set other attributes */
     p->size = 10 * pointSizeScale;
     p->type = trail;
     p->isActive = 1;

     /* our array has expanded at the end */
     num_active_particles++;

 }

 /*
     spawns a new emitter particle at the bottom of the screen
     destined for the point (x,y).
 */
 void
 spawnEmitterParticle(GLfloat x, GLfloat y)
 {

     if (num_active_particles >= MAX_PARTICLES)
         return;

     /* find particle at endpoint of array */
     struct particle *p = &particles[num_active_particles];

     /* set the color randomly */
     switch (rand() % 4) {
     case 0:
         p->color[0] = 255;
         p->color[1] = 100;
         p->color[2] = 100;
         break;
     case 1:
         p->color[0] = 100;
         p->color[1] = 255;
         p->color[2] = 100;
         break;
     case 2:
         p->color[0] = 100;
         p->color[1] = 100;
         p->color[2] = 255;
         break;
     case 3:
         p->color[0] = 255;
         p->color[1] = 150;
         p->color[2] = 50;
         break;
     }
     p->color[3] = 255;
     /* set position to (x, screen_h) */
     p->x = x;
     p->y = screen_h;
     /* set velocity so that terminal point is (x,y) */
     p->xvel = 0;
     p->yvel = -sqrt(2 * ACCEL * (screen_h - y));
     /* set other attributes */
     p->size = 10 * pointSizeScale;
     p->type = emitter;
     p->isActive = 1;
     /* our array has expanded at the end */
     num_active_particles++;
 }

 /* just sets the endpoint of the particle array to element zero */
 void
 initializeParticles(void)
 {
     num_active_particles = 0;
 }

 /*
     loads the particle texture
  */
 void
 initializeTexture()
 {

     int bpp;                    /* texture bits per pixel */
     Uint32 Rmask, Gmask, Bmask, Amask;  /* masks for pixel format passed into OpenGL */
     SDL_Surface *bmp_surface;   /* the bmp is loaded here */
     SDL_Surface *bmp_surface_rgba8888;  /* this serves as a destination to convert the BMP
                                            to format passed into OpenGL */

     bmp_surface = SDL_LoadBMP("stroke.bmp");
     if (bmp_surface == NULL) {
         fatalError("could not load stroke.bmp");
     }

     /* Grab info about format that will be passed into OpenGL */
     SDL_PixelFormatEnumToMasks(SDL_PIXELFORMAT_ABGR8888, &bpp, &Rmask, &Gmask,
                                &Bmask, &Amask);
     /* Create surface that will hold pixels passed into OpenGL */
     bmp_surface_rgba8888 =
         SDL_CreateRGBSurface(0, bmp_surface->w, bmp_surface->h, bpp, Rmask,
                              Gmask, Bmask, Amask);
     /* Blit to this surface, effectively converting the format */
     SDL_BlitSurface(bmp_surface, NULL, bmp_surface_rgba8888, NULL);

     glGenTextures(1, &particleTextureID);
     glBindTexture(GL_TEXTURE_2D, particleTextureID);
     glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA,
                  nextPowerOfTwo(bmp_surface->w),
                  nextPowerOfTwo(bmp_surface->h),
                  0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
     /* this is where we actually pass in the pixel data */
     glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, bmp_surface->w, bmp_surface->h, 0,
                  GL_RGBA, GL_UNSIGNED_BYTE, bmp_surface_rgba8888->pixels);

     /* free bmp surface and converted bmp surface */
     SDL_FreeSurface(bmp_surface);
     SDL_FreeSurface(bmp_surface_rgba8888);

 }

 int
 main(int argc, char *argv[])
 {
     SDL_Window *window;         /* main window */
     SDL_GLContext context;
     int drawableW, drawableH;
     int done;                   /* should we clean up and exit? */

     /* initialize SDL */
     if (SDL_Init(SDL_INIT_VIDEO) < 0) {
         fatalError("Could not initialize SDL");
     }
     /* seed the random number generator */
     srand(time(NULL));
     /*
        request some OpenGL parameters
        that may speed drawing
      */
     SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
     SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 6);
     SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
     SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 0);
     SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 0);
     SDL_GL_SetAttribute(SDL_GL_RETAINED_BACKING, 0);
     SDL_GL_SetAttribute(SDL_GL_ACCELERATED_VISUAL, 1);

     SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 1);
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 1);

     /* create main window and renderer */
     window = SDL_CreateWindow(NULL, 0, 0, 320, 480,
                                 SDL_WINDOW_OPENGL | SDL_WINDOW_BORDERLESS | SDL_WINDOW_ALLOW_HIGHDPI);
     context = SDL_GL_CreateContext(window);

     /* The window size and drawable size may be different when highdpi is enabled,
      * due to the increased pixel density of the drawable. */
     SDL_GetWindowSize(window, &screen_w, &screen_h);
     SDL_GL_GetDrawableSize(window, &drawableW, &drawableH);

     /* In OpenGL, point sizes are always in pixels. We don't want them looking
      * tiny on a retina screen. */
     pointSizeScale = (float) drawableH / (float) screen_h;

     /* load the particle texture */
     initializeTexture();

     /*      check if GL_POINT_SIZE_ARRAY_OES is supported
        this is used to give each particle its own size
      */
     pointSizeExtensionSupported =
         SDL_GL_ExtensionSupported("GL_OES_point_size_array");

     /* set up some OpenGL state */
     glDisable(GL_DEPTH_TEST);
     glDisable(GL_CULL_FACE);

     glMatrixMode(GL_MODELVIEW);
     glLoadIdentity();

     glViewport(0, 0, drawableW, drawableH);

     glMatrixMode(GL_PROJECTION);
     glLoadIdentity();
     glOrthof((GLfloat) 0,
              (GLfloat) screen_w,
              (GLfloat) screen_h,
              (GLfloat) 0, 0.0, 1.0);

     glEnable(GL_TEXTURE_2D);
     glEnable(GL_BLEND);
     glBlendFunc(GL_SRC_ALPHA, GL_ONE);
     glEnableClientState(GL_VERTEX_ARRAY);
     glEnableClientState(GL_COLOR_ARRAY);

     glEnable(GL_POINT_SPRITE_OES);
     glTexEnvi(GL_POINT_SPRITE_OES, GL_COORD_REPLACE_OES, 1);

     if (pointSizeExtensionSupported) {
         /* we use this to set the sizes of all the particles */
         glEnableClientState(GL_POINT_SIZE_ARRAY_OES);
     } else {
         /* if extension not available then all particles have size 10 */
         glPointSize(10 * pointSizeScale);
     }

     done = 0;
     /* enter main loop */
     while (!done) {
         SDL_Event event;
         double deltaTime = updateDeltaTime();
         while (SDL_PollEvent(&event)) {
             if (event.type == SDL_QUIT) {
                 done = 1;
             }
             if (event.type == SDL_MOUSEBUTTONDOWN) {
                 int x, y;
                 SDL_GetMouseState(&x, &y);
                 spawnEmitterParticle(x, y);
             }
         }
         stepParticles(deltaTime);
         drawParticles();
         SDL_GL_SwapWindow(window);
         SDL_Delay(1);
     }

     /* delete textures */
     glDeleteTextures(1, &particleTextureID);
     /* shutdown SDL */
     SDL_Quit();

     return 0;
 }
	/*
	* fireworks.c
	* written by Holmes Futrell
	* use however you want
	*/

	#include "SDL.h"
	#include "SDL_opengles.h"
	#include "common.h"
	#include <math.h>
	#include <time.h>

	#define ACCEL 0.0001f /* acceleration due to gravity, units in pixels per millesecond squared */
	#define WIND_RESISTANCE 0.00005f /* acceleration per unit velocity due to wind resistance */
	#define MAX_PARTICLES 2000 /* maximum number of particles displayed at once */

	static GLuint particleTextureID; /* OpenGL particle texture id */
	static SDL_bool pointSizeExtensionSupported; /* is GL_OES_point_size_array supported ? */
	static float pointSizeScale;
	/*
	used to describe what type of particle a given struct particle is.
	emitter - this particle flies up, shooting off trail particles, then finally explodes into dust particles.
	trail - shoots off, following emitter particle
	dust - radiates outwards from emitter explosion
	*/
	enum particleType
	{
	emitter = 0,
	trail,
	dust
	};
	/*
	struct particle is used to describe each particle displayed on screen
	*/
	struct particle
	{
	GLfloat x; /* x position of particle */
	GLfloat y; /* y position of particle */
	GLubyte color[4]; /* rgba color of particle */
	GLfloat size; /* size of particle in pixels */
	GLfloat xvel; /* x velocity of particle in pixels per milesecond */
	GLfloat yvel; /* y velocity of particle in pixels per millescond */
	int isActive; /* if not active, then particle is overwritten */
	enum particleType type; /* see enum particleType */
	} particles[MAX_PARTICLES]; /* this array holds all our particles */

	static int num_active_particles; /* how many members of the particle array are actually being drawn / animated? */
	static int screen_w, screen_h;

	/* function declarations */
	void spawnTrailFromEmitter(struct particle *emitter);
	void spawnEmitterParticle(GLfloat x, GLfloat y);
	void explodeEmitter(struct particle *emitter);
	void initializeParticles(void);
	void initializeTexture();
	int nextPowerOfTwo(int x);
	void drawParticles();
	void stepParticles(double deltaTime);

	/* helper function (used in texture loading)
	returns next power of two greater than or equal to x
	*/
	int
	nextPowerOfTwo(int x)
	{
	int val = 1;
	while (val < x) {
	val *= 2;
	}
	return val;
	}

	/*
	steps each active particle by timestep deltaTime
	*/
	void
	stepParticles(double deltaTime)
	{
	float deltaMilliseconds = deltaTime * 1000;
	int i;
	struct particle *slot = particles;
	struct particle *curr = particles;
	for (i = 0; i < num_active_particles; i++) {
	/* is the particle actually active, or is it marked for deletion? */
	if (curr->isActive) {
	/* is the particle off the screen? */
	if (curr->y > screen_h)
	curr->isActive = 0;
	else if (curr->y < 0)
	curr->isActive = 0;
	if (curr->x > screen_w)
	curr->isActive = 0;
	else if (curr->x < 0)
	curr->isActive = 0;

	/* step velocity, then step position */
	curr->yvel += ACCEL * deltaMilliseconds;
	curr->xvel += 0.0f;
	curr->y += curr->yvel * deltaMilliseconds;
	curr->x += curr->xvel * deltaMilliseconds;

	/* particle behavior */
	if (curr->type == emitter) {
	/* if we're an emitter, spawn a trail */
	spawnTrailFromEmitter(curr);
	/* if we've reached our peak, explode */
	if (curr->yvel > 0.0) {
	explodeEmitter(curr);
	}
	} else {
	float speed =
	sqrt(curr->xvel * curr->xvel + curr->yvel * curr->yvel);
	/* if wind resistance is not powerful enough to stop us completely,
	then apply winde resistance, otherwise just stop us completely */
	if (WIND_RESISTANCE * deltaMilliseconds < speed) {
	float normx = curr->xvel / speed;
	float normy = curr->yvel / speed;
	curr->xvel -=
	normx * WIND_RESISTANCE * deltaMilliseconds;
	curr->yvel -=
	normy * WIND_RESISTANCE * deltaMilliseconds;
	} else {
	curr->xvel = curr->yvel = 0; /* stop particle */
	}

	if (curr->color[3] <= deltaMilliseconds * 0.1275f) {
	/* if this next step will cause us to fade out completely
	then just mark for deletion */
	curr->isActive = 0;
	} else {
	/* otherwise, let's fade a bit more */
	curr->color[3] -= deltaMilliseconds * 0.1275f;
	}

	/* if we're a dust particle, shrink our size */
	if (curr->type == dust)
	curr->size -= deltaMilliseconds * 0.010f;

	}

	/* if we're still active, pack ourselves in the array next
	to the last active guy (pack the array tightly) */
	if (curr->isActive)
	(slot++) = curr;
	} /* endif (curr->isActive) */
	curr++;
	}
	/* the number of active particles is computed as the difference between
	old number of active particles, where slot points, and the
	new size of the array, where particles points */
	num_active_particles = (int) (slot - particles);
	}

	/*
	This draws all the particles shown on screen
	*/
	void
	drawParticles()
	{

	/* draw the background */
	glClear(GL_COLOR_BUFFER_BIT);

	/* set up the position and color pointers */
	glVertexPointer(2, GL_FLOAT, sizeof(struct particle), particles);
	glColorPointer(4, GL_UNSIGNED_BYTE, sizeof(struct particle),
	particles[0].color);

	if (pointSizeExtensionSupported) {
	/* pass in our array of point sizes */
	glPointSizePointerOES(GL_FLOAT, sizeof(struct particle),
	&(particles[0].size));
	}

	/* draw our particles! */
	glDrawArrays(GL_POINTS, 0, num_active_particles);

	}

	/*
	This causes an emitter to explode in a circular bloom of dust particles
	*/
	void
	explodeEmitter(struct particle *emitter)
	{
	/* first off, we're done with this particle, so turn active off */
	emitter->isActive = 0;
	int i;
	for (i = 0; i < 200; i++) {

	if (num_active_particles >= MAX_PARTICLES)
	return;

	/* come up with a random angle and speed for new particle */
	float theta = randomFloat(0, 2.0f * 3.141592);
	float exponent = 3.0f;
	float speed = randomFloat(0.00, powf(0.17, exponent));
	speed = powf(speed, 1.0f / exponent);

	/* select the particle at the end of our array */
	struct particle *p = &particles[num_active_particles];

	/* set the particles properties */
	p->xvel = speed * cos(theta);
	p->yvel = speed * sin(theta);
	p->x = emitter->x + emitter->xvel;
	p->y = emitter->y + emitter->yvel;
	p->isActive = 1;
	p->type = dust;
	p->size = 15 * pointSizeScale;
	/* inherit emitter's color */
	p->color[0] = emitter->color[0];
	p->color[1] = emitter->color[1];
	p->color[2] = emitter->color[2];
	p->color[3] = 255;
	/* our array has expanded at the end */
	num_active_particles++;
	}

	}

	/*
	This spawns a trail particle from an emitter
	*/
	void
	spawnTrailFromEmitter(struct particle *emitter)
	{

	if (num_active_particles >= MAX_PARTICLES)
	return;

	/* select the particle at the slot at the end of our array */
	struct particle *p = &particles[num_active_particles];

	/* set position and velocity to roughly that of the emitter */
	p->x = emitter->x + randomFloat(-3.0, 3.0);
	p->y = emitter->y + emitter->size / 2.0f;
	p->xvel = emitter->xvel + randomFloat(-0.005, 0.005);
	p->yvel = emitter->yvel + 0.1;

	/* set the color to a random-ish orangy type color */
	p->color[0] = (0.8f + randomFloat(-0.1, 0.0)) * 255;
	p->color[1] = (0.4f + randomFloat(-0.1, 0.1)) * 255;
	p->color[2] = (0.0f + randomFloat(0.0, 0.2)) * 255;
	p->color[3] = (0.7f) * 255;

	/* set other attributes */
	p->size = 10 * pointSizeScale;
	p->type = trail;
	p->isActive = 1;

	/* our array has expanded at the end */
	num_active_particles++;

	}

	/*
	spawns a new emitter particle at the bottom of the screen
	destined for the point (x,y).
	*/
	void
	spawnEmitterParticle(GLfloat x, GLfloat y)
	{

	if (num_active_particles >= MAX_PARTICLES)
	return;

	/* find particle at endpoint of array */
	struct particle *p = &particles[num_active_particles];

	/* set the color randomly */
	switch (rand() % 4) {
	case 0:
	p->color[0] = 255;
	p->color[1] = 100;
	p->color[2] = 100;
	break;
	case 1:
	p->color[0] = 100;
	p->color[1] = 255;
	p->color[2] = 100;
	break;
	case 2:
	p->color[0] = 100;
	p->color[1] = 100;
	p->color[2] = 255;
	break;
	case 3:
	p->color[0] = 255;
	p->color[1] = 150;
	p->color[2] = 50;
	break;
	}
	p->color[3] = 255;
	/* set position to (x, screen_h) */
	p->x = x;
	p->y = screen_h;
	/* set velocity so that terminal point is (x,y) */
	p->xvel = 0;
	p->yvel = -sqrt(2 * ACCEL * (screen_h - y));
	/* set other attributes */
	p->size = 10 * pointSizeScale;
	p->type = emitter;
	p->isActive = 1;
	/* our array has expanded at the end */
	num_active_particles++;
	}

	/* just sets the endpoint of the particle array to element zero */
	void
	initializeParticles(void)
	{
	num_active_particles = 0;
	}

	/*
	loads the particle texture
	*/
	void
	initializeTexture()
	{

	int bpp; /* texture bits per pixel */
	Uint32 Rmask, Gmask, Bmask, Amask; /* masks for pixel format passed into OpenGL */
	SDL_Surface bmp_surface; / the bmp is loaded here */
	SDL_Surface bmp_surface_rgba8888; / this serves as a destination to convert the BMP
	to format passed into OpenGL */

	bmp_surface = SDL_LoadBMP("stroke.bmp");
	if (bmp_surface == NULL) {
	fatalError("could not load stroke.bmp");
	}

	/* Grab info about format that will be passed into OpenGL */
	SDL_PixelFormatEnumToMasks(SDL_PIXELFORMAT_ABGR8888, &bpp, &Rmask, &Gmask,
	&Bmask, &Amask);
	/* Create surface that will hold pixels passed into OpenGL */
	bmp_surface_rgba8888 =
	SDL_CreateRGBSurface(0, bmp_surface->w, bmp_surface->h, bpp, Rmask,
	Gmask, Bmask, Amask);
	/* Blit to this surface, effectively converting the format */
	SDL_BlitSurface(bmp_surface, NULL, bmp_surface_rgba8888, NULL);

	glGenTextures(1, &particleTextureID);
	glBindTexture(GL_TEXTURE_2D, particleTextureID);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA,
	nextPowerOfTwo(bmp_surface->w),
	nextPowerOfTwo(bmp_surface->h),
	0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	/* this is where we actually pass in the pixel data */
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, bmp_surface->w, bmp_surface->h, 0,
	GL_RGBA, GL_UNSIGNED_BYTE, bmp_surface_rgba8888->pixels);

	/* free bmp surface and converted bmp surface */
	SDL_FreeSurface(bmp_surface);
	SDL_FreeSurface(bmp_surface_rgba8888);

	}

	int
	main(int argc, char *argv[])
	{
	SDL_Window window; / main window */
	SDL_GLContext context;
	int drawableW, drawableH;
	int done; /* should we clean up and exit? */

	/* initialize SDL */
	if (SDL_Init(SDL_INIT_VIDEO) < 0) {
	fatalError("Could not initialize SDL");
	}
	/* seed the random number generator */
	srand(time(NULL));
	/*
	request some OpenGL parameters
	that may speed drawing
	*/
	SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
	SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 6);
	SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
	SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 0);
	SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 0);
	SDL_GL_SetAttribute(SDL_GL_RETAINED_BACKING, 0);
	SDL_GL_SetAttribute(SDL_GL_ACCELERATED_VISUAL, 1);

	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 1);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 1);

	/* create main window and renderer */
	window = SDL_CreateWindow(NULL, 0, 0, 320, 480,
	SDL_WINDOW_OPENGL \| SDL_WINDOW_BORDERLESS \| SDL_WINDOW_ALLOW_HIGHDPI);
	context = SDL_GL_CreateContext(window);

	/* The window size and drawable size may be different when highdpi is enabled,
	* due to the increased pixel density of the drawable. */
	SDL_GetWindowSize(window, &screen_w, &screen_h);
	SDL_GL_GetDrawableSize(window, &drawableW, &drawableH);

	/* In OpenGL, point sizes are always in pixels. We don't want them looking
	* tiny on a retina screen. */
	pointSizeScale = (float) drawableH / (float) screen_h;

	/* load the particle texture */
	initializeTexture();

	/* check if GL_POINT_SIZE_ARRAY_OES is supported
	this is used to give each particle its own size
	*/
	pointSizeExtensionSupported =
	SDL_GL_ExtensionSupported("GL_OES_point_size_array");

	/* set up some OpenGL state */
	glDisable(GL_DEPTH_TEST);
	glDisable(GL_CULL_FACE);

	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();

	glViewport(0, 0, drawableW, drawableH);

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrthof((GLfloat) 0,
	(GLfloat) screen_w,
	(GLfloat) screen_h,
	(GLfloat) 0, 0.0, 1.0);

	glEnable(GL_TEXTURE_2D);
	glEnable(GL_BLEND);
	glBlendFunc(GL_SRC_ALPHA, GL_ONE);
	glEnableClientState(GL_VERTEX_ARRAY);
	glEnableClientState(GL_COLOR_ARRAY);

	glEnable(GL_POINT_SPRITE_OES);
	glTexEnvi(GL_POINT_SPRITE_OES, GL_COORD_REPLACE_OES, 1);

	if (pointSizeExtensionSupported) {
	/* we use this to set the sizes of all the particles */
	glEnableClientState(GL_POINT_SIZE_ARRAY_OES);
	} else {
	/* if extension not available then all particles have size 10 */
	glPointSize(10 * pointSizeScale);
	}

	done = 0;
	/* enter main loop */
	while (!done) {
	SDL_Event event;
	double deltaTime = updateDeltaTime();
	while (SDL_PollEvent(&event)) {
	if (event.type == SDL_QUIT) {
	done = 1;
	}
	if (event.type == SDL_MOUSEBUTTONDOWN) {
	int x, y;
	SDL_GetMouseState(&x, &y);
	spawnEmitterParticle(x, y);
	}
	}
	stepParticles(deltaTime);
	drawParticles();
	SDL_GL_SwapWindow(window);
	SDL_Delay(1);
	}

	/* delete textures */
	glDeleteTextures(1, &particleTextureID);
	/* shutdown SDL */
	SDL_Quit();

	return 0;
	}