sdlbrot.cpp

#include "SDL.h"
#include <stdlib.h>
#include <math.h>

struct Rect
{
    Rect() : x0(0), y0(0), x1(0), y1(0) {}
    Rect(double a0, double b0, double a1, double b1) :
        x0(a0), y0(b0), x1(a1), y1(b1) {}

    double width() const { return fabsl(x1 - x0); }
    double height() const { return fabsl(y1 - y0); }

    double x0; double y0;
    double x1; double y1;
};

static int _max_iteration = 50;
static SDL_Surface *screen;
static Rect r(-2, 1, 1, -1);

#define WIDTH  640
#define HEIGHT 480

extern "C" {
    void clear();
}

inline void plot(SDL_Surface *screen, int x, int y, int r, int g, int b)
{
    int pitch = WIDTH * 4;
    int bpp = 4;
    int offset = y * pitch + x * bpp;

    ((uint8_t *)screen->pixels)[offset] = r;
    ((uint8_t *)screen->pixels)[offset + 1] = g;
    ((uint8_t *)screen->pixels)[offset + 2] = b;
    ((uint8_t *)screen->pixels)[offset + 3] = 1; // XXX: alpha doesn't matter
}

void draw(const Rect &rect)
{
    printf("Drawing: %.2f, %.2f, %.2f, %.2f\n",
            rect.x0, rect.y0, rect.x1, rect.y1);

    clear();

    SDL_LockSurface(screen);

    // XXX: SDL_FillRect not yet implemented by emscripten
//    SDL_FillRect(screen, NULL, SDL_MapRGB(screen->format, 0, 0, 0));

    // XXX: screen attributes not properly set by emscripten
//    int width = screen->w, height = screen->h;
    int width = WIDTH, height = HEIGHT;
    double dx = (rect.x1 - rect.x0) / width;
    double dy = (rect.y1 - rect.y0) / height;
    double x = rect.x0, y = rect.y0;

    // Naive Mandelbrot algorithm.
    for (int i = 0; i < width; ++i) {
        for (int j = 0; j < height; ++j) {
            double z = 0.0, zi = 0.0;

            int v = 0;
            int n = 0;
            while ((n < _max_iteration)) {
                double z_ = z*z - zi*zi + x;
                zi = 2*z*zi + y;
                z = z_;

                if (z*z + zi*zi > 4) {
                    // XXX: color hack
                    v = round((float) 240 * n / _max_iteration) + 15;
                    break;
                }
                ++n;
            }

            static int count = 0;

            if (v) {
                if (count < 50) {
                    count++;
                }

                plot(screen, i, j, 0, v, v);
            } else {
                // interior point
//                plot(screen, i, j, 255, 0, 0);
            }

            y += dy;
        }

        x += dx;
        y = rect.y0;
    }

    SDL_UnlockSurface(screen);
    SDL_Flip(screen);
}

extern "C" {
    void zoom(int zoomX, int zoomY)
    {
        // XXX hacky zoom
        double zoom = 1.5;
        double x = (double) zoomX / WIDTH;
        double y = (double) zoomY / HEIGHT;
        double w = r.width();
        double h = r.height();

        r.x0 += (w * x) - (w / zoom / 2);
        r.y0 -= (h * y) - (h / zoom / 2);
        r.x1 = r.x0 + (w / zoom);
        r.y1 = r.y0 - (h / zoom);

        draw(r);
    }
}

int main(int argc, char **argv)
{
    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_NOPARACHUTE) < 0) {
        printf("ERROR: %s\n", SDL_GetError());
        exit(1);
    }

    screen = SDL_SetVideoMode(WIDTH, HEIGHT, 32, 0);
    if (!screen) {
        printf("ERROR: %s\n", SDL_GetError());
        exit(1);
    }

    draw(r);

    // XXX: this info is garbage in emscripten's impl
#if 0
    // Debug info.
    printf("Created screen:\n");
    printf("\tDimensions: %d x %d\n", screen->w, screen->h);
    printf("\tPitch: %d\n", screen->pitch);
    printf("\tData: %p\n", screen->pixels);
    printf("\tBPP: %d\n", screen->format->BitsPerPixel);

    // XXX: events not yet supported by emscripten
    SDL_Event event;
    bool dirty = true;

    while (SDL_WaitEvent(&event)) {
        if (dirty) {
            dirty = false;
            draw(screen, r);
            SDL_Flip(screen);
        }

        switch (event.type) {
            case SDL_MOUSEBUTTONDOWN: 
                dirty = true;

                {
                    // XXX hacky zoom
                    double zoom = 1.5;
                    double x = (double) event.button.x / screen->w;
                    double y = (double) event.button.y / screen->h;
                    double w = r.width();
                    double h = r.height();

                    r.x0 += (w * x) - (w / zoom / 2);
                    r.y0 -= (h * y) - (h / zoom / 2);
                    r.x1 = r.x0 + (w / zoom);
                    r.y1 = r.y0 - (h / zoom);
                }
                break;

            case SDL_KEYDOWN:
                switch (event.key.keysym.sym) {
                    case SDLK_ESCAPE:
                        printf("Adios!\n");
                        exit(0);
                        break;

                    case SDLK_UP:
                        dirty = true;
                        _max_iteration += 10;
                        break;

                    case SDLK_DOWN:
                        dirty = true;
                        _max_iteration -= (_max_iteration > 20) ? 10 : 0;
                        break;

                    case SDLK_SPACE:
                        // Reset.
                        dirty = true;
                        r = Rect(-2, 1, 1, -1);
                        _max_iteration = 50;
                        break;
                }
                break;
        }
    }

    SDL_Quit();
#endif
    return 0;
}