Physics demo

demo.c

// $ eval cc -g3 -o demo demo.c $(pkg-config --cflags --libs sdl2)
// Ref: https://old.reddit.com/r/C_Programming/comments/1prwizy
// Ref: https://github.com/Avery-Personal/Jubi
#define JUBI_IMPLEMENTATION
#include "Jubi.h"
#include "SDL.h"

static Sint32 randn(Uint64 *s, Sint32 lo, Sint32 hi)
{
    *s = *s*0x3243f6a8885a308d + 1;
    return (Sint32)((*s>>32)*(Uint64)(hi - lo)>>32) + lo;
}

static SDL_FRect tofrect(Body2D *b)
{
    return (SDL_FRect){
        b->Position.x - b->_Size.x/2,
        b->Position.y - b->_Size.y/2,
        b->_Size.x,
        b->_Size.y,
    };
}

int main(int, char **)
{
    int x      = SDL_WINDOWPOS_UNDEFINED;
    int y      = SDL_WINDOWPOS_UNDEFINED;
    int width  = 800;
    int height = 800;

    SDL_Init(SDL_INIT_VIDEO);
    SDL_Window   *w = SDL_CreateWindow("Jubi", x, y, width, height, 0);
    SDL_Renderer *r = SDL_CreateRenderer(w, -1, SDL_RENDERER_PRESENTVSYNC);

    JubiWorld2D world = Jubi_CreateWorld2D();

    Body2D *floor = JBody2D_CreateBox(
        &world,
        (Vector2){(float)width/2, (float)height-5},
        (Vector2){(float)width, 10},
        BODY_STATIC, 1000
    );

    enum { N = 16 };
    Uint64  rng       = 1234;
    Body2D *box[N]    = {};
    Sint32  colors[N] = {};
    for (int i = 0; i < N; i++) {
        float  x = (float)randn(&rng, 0, width);
        float  y = (float)randn(&rng, 0, height);
        float  w = (float)randn(&rng, width/30, width/10);
        float  h = (float)randn(&rng, width/30, width/10);
        Sint32 r = randn(&rng, 0, 256) | 0x40;
        Sint32 g = randn(&rng, 0, 256) | 0x40;
        Sint32 b = randn(&rng, 0, 256) | 0x40;
        box[i] = JBody2D_CreateBox(
            &world,
            (Vector2){x, y},
            (Vector2){w, h},
            BODY_DYNAMIC, 1
        );
        colors[i] = r<<16 | g<<8 | b;
    }

    Sint64 last = (Sint64)SDL_GetTicks64();
    for (;;) {
        for (SDL_Event e; SDL_PollEvent(&e);) {
            switch (e.type) {
            case SDL_QUIT:
                return 0;
            }
        }

        SDL_SetRenderDrawColor(r, 0, 0, 0, 0);
        SDL_RenderClear(r);

        SDL_SetRenderDrawColor(r, 255, 0, 0, 255);
        SDL_FRect fr = tofrect(floor);
        SDL_RenderFillRectF(r, &fr);

        for (int i = 0; i < N; i++) {
            SDL_FRect fr = tofrect(box[i]);
            SDL_SetRenderDrawColor(
                r, 
                (Uint8)(colors[i]>>16),
                (Uint8)(colors[i]>> 8),
                (Uint8)(colors[i]>> 0),
                255
            );
            SDL_RenderFillRectF(r, &fr);
        }
        SDL_RenderPresent(r);
        SDL_Delay(1);

        Sint64 now = (Sint64)SDL_GetTicks64();
        Jubi_StepWorld2D(&world, 1 / (float)(now - last));
        last = now;
    }
}