colored square

#include <stdlib.h>
#include <stdio.h>
#include <SDL/SDL.h>
#include <math.h>

typedef struct {
    Uint8 r;
    Uint8 g;
    Uint8 b;
} pixel;

void pause();
void setPixel(SDL_Surface* screen, int x, int y, pixel* p);

int main(int argc, char *argv[]) {
    SDL_Surface *ecran = NULL;

    if (SDL_Init(SDL_INIT_VIDEO) == -1) {
        fprintf(stderr, "Erreur d'initialisation de la SDL : %s\n", SDL_GetError());
        exit(EXIT_FAILURE);
    }

    ecran = SDL_SetVideoMode(512, 512, 32, SDL_HWSURFACE);
    if (ecran == NULL) {
        fprintf(stderr, "Erreur d'initialisation du mode vidéo : %s\n", SDL_GetError());
        exit(EXIT_FAILURE);
    }
    SDL_WM_SetCaption("Test SDL", NULL);

    pixel pv1 = {255, 0, 0};
    pixel pv2 = {0, 255, 0};
    pixel pv3 = {0, 0, 255};
    pixel pv4 = {255, 255, 255};
    pixel p = {0, 0, 0};
    float d1, d2, d3, w1, w2, w3;
    for (int x = 0; x < 512; x++) {
        for (int y = 0; y <= x; y++) {
            w1 = (float)((-512)*(x-512))/(float)(pow(-512,2));
            w2 = (float)(512*(x-512)+(-512)*(y-512))/(float)(pow(-512,2));
            w3 = 1-w1-w2;
            p.r = (float)((float)pv1.r*w1+(float)pv2.r*w2+(float)pv3.r*w3)/(w1+w2+w3);
            p.g = (float)((float)pv1.g*w1+(float)pv2.g*w2+(float)pv3.g*w3)/(w1+w2+w3);
            p.b = (float)((float)pv1.b*w1+(float)pv2.b*w2+(float)pv3.b*w3)/(w1+w2+w3);
            //p.b = (int)((float)pv1.b*w1+(float)pv2.b*w2+(float)pv3.b*w3);
            setPixel(ecran, x, y,&p);
        }
        for (int y = x; y < 512; y++) {
            w1 = (float)(512*(y-512))/(float)(512*(-512));
            w2 = (float)(512*(x-512)+(-512)*(y-512))/(float)(512*(-512));
            w3 = 1-w1-w2;
            p.r = (float)((float)pv1.r*w1+(float)pv4.r*w2+(float)pv3.r*w3)/(w1+w2+w3);
            p.g = (float)((float)pv1.g*w1+(float)pv4.g*w2+(float)pv3.g*w3)/(w1+w2+w3);
            p.b = (float)((float)pv1.b*w1+(float)pv4.b*w2+(float)pv3.b*w3)/(w1+w2+w3);
            setPixel(ecran, x, y,&p);
        }
    }

    SDL_Flip(ecran);

    pause();

    SDL_Quit();
    return EXIT_SUCCESS;
}

void setPixel(SDL_Surface* screen, int x, int y, pixel* p) {
    Uint32* p_screen = (Uint32*)screen->pixels;
    p_screen += y* screen->w+x;
    *p_screen = SDL_MapRGB(screen->format, p->r, p->g, p->b);
}

void pause() {
    int continuer = 1;
    SDL_Event event;

    while(continuer) {
        SDL_WaitEvent(&event);
        switch(event.type) {
        case SDL_QUIT:
            continuer = 0;
        }
    }
}