GIF Writer

jo_gif.cpp
File Size:	13 kb
File Type:	cpp

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This post is to announce my stb style 398 LoC animated GIF writer. 

The primary features are
1) 398 lines of code
2) No memory allocations
3) Public Domain
4) NeuQuant based quantizer

I think there is still a lot left that could be done here with it, but I feel its a good version 1.0.

Namely, missing alpha support. Easy to do, but needs to be done. Also some improvements to the color quantization. After going through NeuQuant I found quite a few things which I feel can be improved which I hope I have time to get to. 

Basic Usage:

// 4 component. RGBX format, where X is unused 
char *frame = new char[128*128*4]; 
jo_gif_t gif = jo_gif_start("foo.gif", 128, 128, 0, 32);    
jo_gif_frame(&gif, frame, 4, false); // frame 1
jo_gif_frame(&gif, frame, 4, false); // frame 2
jo_gif_frame(&gif, frame, 4, false); // frame 3, ...
jo_gif_end(&gif);

Where frame holds the RGBA pixels for a frame. You call start, then frame a bunch of times then end. 

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Here is a more interesting example used to create the image above. :) Enjoy!

void hsv2rgb(float hsv[3], float rgb[3]) {
    if(hsv[1] <= 0.0) {       // < is bogus, just shuts up warnings
        rgb[0] = rgb[1] = rgb[2] = hsv[2];
        return;
    }
    float hh = hsv[0];
    if(hh >= 360) {
        hh = 0;
    }
    hh /= 60;
    long i = (long)hh;
    float ff = hh - i;
    float p = hsv[2] * (1.f - hsv[1]);
    float q = hsv[2] * (1.f - (hsv[1] * ff));
    float t = hsv[2] * (1.f - (hsv[1] * (1.f - ff)));
    switch(i) {
        case 0: rgb[0] = hsv[2]; rgb[1] = t; rgb[2] = p; break;
        case 1: rgb[0] = q; rgb[1] = hsv[2]; rgb[2] = p; break;
        case 2: rgb[0] = p; rgb[1] = hsv[2]; rgb[2] = t; break;
        case 3: rgb[0] = p; rgb[1] = q; rgb[2] = hsv[2]; break;
        case 4: rgb[0] = t; rgb[1] = p; rgb[2] = hsv[2]; break;
        case 5: rgb[0] = hsv[2]; rgb[1] = p; rgb[2] = q; break;
    }
}

int main(int argc, char **argv) {
    const int w = 256, h = 256;
    jo_gif_t gif = jo_gif_start("foo.gif", w,h,0,32);
    for(int frame = 0; frame < 360/4; ++frame) {
        unsigned char tmp[w*h*4];
        double coordX = -0.74529;
        double coordY = 0.113075;
        double zoom = 1.5E-4*0.5;
        for(int y = 0; y < h; ++y) {
            for(int x = 0; x < w; ++x) {
                double x0 = (x/double(w) * 3.5 - 2.5) * zoom + coordX;
                double y0 = (y/double(h) * 3.0 - 1.5) * zoom + coordY;
                double xx = 0, yy = 0;
                int iter = 0;
                while(xx*xx + yy*yy < 2*2 && iter++ < 4096) {
                    double xtmp = xx*xx - yy*yy + x0;
                    yy = 2*xx*yy + y0;
                    xx = xtmp;
                }
                int i = y*w*4+x*4;
                int iter2 = iter + 360 - frame*4;
                float hsv[3] = { float(iter2%360), 1, iter2 < 4096 ? 1.f : 0.f };
                float rgb[3];
                hsv2rgb(hsv, rgb);
                tmp[i+0] = (unsigned char)(rgb[0] * 255);
                tmp[i+1] = (unsigned char)(rgb[1] * 255);
                tmp[i+2] = (unsigned char)(rgb[2] * 255);
                tmp[i+3] = 255;
            }
        }
        jo_gif_frame(&gif, tmp, 4, false);
    }
    jo_gif_end(&gif);
}