/*

  Compile with:

    gcc -o gif2png-gdk-pixbuf gif2png-gdk-pixbuf.c `pkg-config cairo gdk-2.0 gdk-pixbuf-2.0 --cflags --libs`

*/
#include <cairo/cairo.h>
#include <gdk/gdk.h>
#include <gdk-pixbuf/gdk-pixbuf.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define TARGET_WIDTH 2000
#define TARGET_HEIGHT 2000

#define BUFFER_SIZE 4096

#ifndef MIN
# define MIN(a,b) ((a)<(b)?(a):(b))
#endif

typedef struct{
    GdkPixbufAnimation *animation;
}image_t;

typedef struct{
    image_t *image;
    GdkPixbuf *pixbuf;
}frame_t;


image_t *
testcase_load(const char *filename){
    image_t *image = (image_t*)malloc(sizeof(image_t));
    FILE* f;
    GdkPixbufLoader *loader;

    f = fopen(filename, "r");
    if(!f)
        return NULL;

    loader = gdk_pixbuf_loader_new_with_mime_type ("image/gif", NULL);
    if(!loader)
        return NULL;

    for(;;){
        guchar buffer[BUFFER_SIZE];
        ssize_t read_bytes;
        read_bytes = fread(buffer, 1, BUFFER_SIZE, f);
        if (read_bytes < 0)
            return NULL;

        if(0 == read_bytes)
            break;

        if(!gdk_pixbuf_loader_write(loader, buffer, read_bytes, NULL))
            return NULL;
    }
    /* Loading complete, transaction should not be free-ed */
    gdk_pixbuf_loader_close(loader, NULL);

    fclose(f);

    image->animation = gdk_pixbuf_loader_get_animation(loader);

    return image;
}


frame_t *
testcase_frame(image_t *image,int nr){
    frame_t *frame = (frame_t*)malloc(sizeof(frame_t));
    GdkPixbufAnimationIter *iter;

    frame->image = image;

    iter = gdk_pixbuf_animation_get_iter(image->animation, NULL);
    while(nr-->0){
        /* Here the frame number could be advanced but that is too
           complicated to bother with here. */
    }
    frame->pixbuf = gdk_pixbuf_animation_iter_get_pixbuf(iter);

    return frame;
}


void
testcase_draw(frame_t *frame,cairo_t *cr){
    int width;
    int height;
    double x_offset;
    double y_offset;
    double scale;

    /* Calculate scale */
    width = gdk_pixbuf_animation_get_width(frame->image->animation);
    height = gdk_pixbuf_animation_get_height(frame->image->animation);
    scale = MIN((double)TARGET_WIDTH/width,(double)TARGET_HEIGHT/height);
    x_offset = (TARGET_WIDTH - scale*width)/2;
    y_offset = (TARGET_HEIGHT - scale*height)/2;

    cairo_translate(cr, x_offset, y_offset);
    cairo_scale(cr, scale, scale);

    gdk_cairo_set_source_pixbuf(cr, frame->pixbuf, 0, 0);
    cairo_paint(cr);
}


static clock_t start;

static void
measuretime_start(){
     start = clock();
}

static double
measuretime_point(){
     clock_t now = clock();
     return (double) (now - start) / CLOCKS_PER_SEC;
}


int
main(int argc,char **argv){
    cairo_surface_t *surface;
    cairo_t *cr;
    image_t *image;
    frame_t *frame;
    if(argc<2){
        fprintf(stderr,"Usage: %s <filename.gif> [<filename.png>]\n",argv[0]);
        return 1;
    }

    /* Create a surface to render the image on */
    surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32,TARGET_WIDTH,TARGET_HEIGHT);
    cr = cairo_create(surface);

    /* Load the image */
    measuretime_start();
    image = testcase_load(argv[1]);
    if(!image){
        fprintf(stderr,"Failed to load GIF image %s\n",argv[1]);
        return 1;
    }
    printf("Loading the image took %f seconds\n",measuretime_point());

    /* Get a frame */
    measuretime_start();
    frame = testcase_frame(image,0);
    printf("Getting a frame took %f seconds\n",measuretime_point());

    /* Render the frame (scaled) */
    measuretime_start();
    testcase_draw(frame,cr);
    printf("Rendering the frame took %f seconds\n",measuretime_point());

    /* Optionally save the result */
    if(argc>=3)
    cairo_surface_write_to_png(surface,argv[2]);
    return 0;
}