ref: a14aa30bde008fe40c6a6f846a0c5e687b7c249f
dir: /external/SDL2/Xcode-iOS/Demos/src/fireworks.c/
/*
* 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;
}