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Basic particle simulation using SDL

ben353 (4)
Hey, so I'm making just a very basic (and not particularly realistic!) particle simulation. The idea is I want to add a much larger 'particle' i.e. one big circle which again moves randomly around. The way I stop the little particles colliding so far is using booleans and so I was wondering how I could set all the pixels within the larger circle to 'true' using what I already have. Any help would be much appreciated!


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#include <cmath>
#include <cstdlib>
#include <ctime>
#include <string>
#include <sstream>
#include <vector>

#include "Graphics.hpp"
											
Graphics *gfx;
std::vector<int> x_disp;
std::vector<int> y_disp;
int n_particles=1000;
int width=800;
int height=600;

std::vector<bool> look_up(width*height,false);

void draw_pixels() {
	gfx->clearScreen(gfx->BLACK);
	for (int i=0; i<n_particles; i++) {
		gfx->setPixel(x_disp[i],y_disp[i],gfx->WHITE);
	}
	gfx->flipScreen();
}


int main() {
	srand(time(NULL));
	// initialise graphics

	gfx=new Graphics();
	gfx->init(width,height);

	bool closed=false;
   SDL_Event event;

	// set initial positions
	for (int i=0; i<n_particles; i++) {
		x_disp.push_back(rand()%800);
		y_disp.push_back(rand()%600);
		look_up[x_disp[i]*y_disp[i]]=true;
		// set relevant index in the lookup array to true 
	}

		//int rr = 20;
		//gfx->circle(x_circle, y_circle, rr, gfx->GREEN); //Here is where I want to make a circle where all the pixels contained within are set to true
																			// so that the other little pixel 'particles' don't enter it.


	// enter the event loop
	while(!closed) {

		// small delay
		gfx->delay(10);
		draw_pixels();
		
		for (int i=0; i<n_particles; i++) {
			if (y_disp[i]<0) {						//Checks for wrap around
				y_disp[i] +=height;
			}
			if (y_disp[i]>height-1) {				//''
				y_disp[i] -= height;
			}
			if (x_disp[i]<0) {						//''
				x_disp[i] += width;
			}
			if (x_disp[i] > width-1) {				//''
				x_disp[i] -= width;
			}
		}

		// update positions
		for (int i=0; i<n_particles; i++) {
			// choose random direction
			int dir=rand()%4;
			switch(dir) {
				case 0 : // N
					if (look_up[x_disp[i]*(y_disp[i]--)]=true) {
						break;
					}
					else {
						look_up[x_disp[i]*y_disp[i]]=false;
						y_disp[i]--;
						look_up[x_disp[i]*y_disp[i]]=true;
						break;
					}	
				case 1 : // E
					if (look_up[(x_disp[i]++)*y_disp[i]]=true) {
						break;
					}
					else {
						look_up[x_disp[i]*y_disp[i]]=false;
						x_disp[i]++;
						look_up[x_disp[i]*y_disp[i]]=true;
						break;	
					}	
				case 2 : // S
					if (look_up[(x_disp[i])*(y_disp[i]++)]=true) {
						break;
					}
					else {
						look_up[x_disp[i]*y_disp[i]]=false;
						y_disp[i]++;
						look_up[x_disp[i]*y_disp[i]]=true;
						break;
					}		
				case 3 : // W
					if (look_up[(x_disp[i]--)*(y_disp[i])]=true) {
						break;
					}
					else {
						look_up[x_disp[i]*y_disp[i]]=false;
						x_disp[i]--;
						look_up[x_disp[i]*y_disp[i]]=true;
						break;
					}		
			}
		}
		while(SDL_PollEvent(&event)) {
			switch (event.type) {

				// react to the QUIT event (i.e. closing the window)
				case SDL_QUIT:
					closed = true;
					break;
			}
		}
	}

	// clean up graphics
	delete gfx;

	return 0;
}
Last edited on
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