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#include <stdio.h>
#include <stdlib.h>
#include <stdexcept>
extern "C" {
#include <ass.h>
}
#include <png.h>
struct image_t {
int width, height, stride;
unsigned char* buffer; // RGB24
};
ass_library_t* ass_library;
ass_renderer_t* ass_renderer;
static void write_png(char *fname, image_t* img)
{
FILE * fp;
png_structp png_ptr;
png_infop info_ptr;
png_byte **row_pointers;
int k;
png_ptr = png_create_write_struct (PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
info_ptr = png_create_info_struct(png_ptr);
fp = NULL;
if (setjmp(png_ptr->jmpbuf)) {
png_destroy_write_struct(&png_ptr, &info_ptr);
fclose(fp);
return;
}
fp = fopen (fname, "wb");
if (fp == NULL) {
printf("PNG Error opening %s for writing!\n", fname);
return;
}
png_init_io(png_ptr, fp);
png_set_compression_level(png_ptr, 0);
png_set_IHDR(png_ptr, info_ptr, img->width, img->height,
8, PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE,
PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
png_write_info(png_ptr, info_ptr);
png_set_bgr(png_ptr);
row_pointers = (png_byte **)malloc(img->height * sizeof(png_byte*));
for (k = 0; k < img->height; k++)
row_pointers[k] = img->buffer + img->stride * k;
png_write_image(png_ptr, row_pointers);
png_write_end(png_ptr, info_ptr);
png_destroy_write_struct(&png_ptr, &info_ptr);
free(row_pointers);
fclose (fp);
}
static void init(int frame_w, int frame_h) {
ass_library = ass_library_init();
if (!ass_library) throw std::runtime_error("ass_library_init failed");
ass_set_fonts_dir(ass_library, "");
ass_set_extract_fonts(ass_library, 0);
ass_set_style_overrides(ass_library, NULL);
ass_renderer = ass_renderer_init(ass_library);
if (!ass_renderer) throw std::runtime_error("ass_renderer_init failed");
ass_set_frame_size(ass_renderer, frame_w, frame_h);
ass_set_margins(ass_renderer, 0, 0, 0, 0);
ass_set_use_margins(ass_renderer, 0);
ass_set_font_scale(ass_renderer, 1.);
ass_set_fonts(ass_renderer, NULL, "Sans");
}
static image_t* gen_image(int width, int height) {
image_t* img = new image_t;
img->width = width;
img->height = height;
img->stride = width * 3;
img->buffer = (unsigned char*)calloc(1, height * width * 3);
for (int i = 0; i < height * width * 3; ++i)
img->buffer[i] = (i/3/50) % 100;
return img;
}
#define _r(c) ((c)>>24)
#define _g(c) (((c)>>16)&0xFF)
#define _b(c) (((c)>>8)&0xFF)
#define _a(c) ((c)&0xFF)
static void blend_single(image_t* frame, ass_image_t* img) {
unsigned char opacity = 255 - _a(img->color);
unsigned char r = _r(img->color);
unsigned char g = _g(img->color);
unsigned char b = _b(img->color);
unsigned char* src;
unsigned char* dst;
src = img->bitmap;
dst = frame->buffer + img->dst_y * frame->stride + img->dst_x * 3;
for (int y = 0; y < img->h; ++y) {
for (int x = 0; x < img->w; ++x) {
unsigned k = ((unsigned)src[x]) * opacity / 255;
// possible endianness problems
dst[x*3] = (k*b + (255-k)*dst[x*3]) / 255;
dst[x*3+1] = (k*g + (255-k)*dst[x*3+1]) / 255;
dst[x*3+2] = (k*r + (255-k)*dst[x*3+2]) / 255;
}
src += img->stride;
dst += frame->stride;
}
}
static void blend(image_t* frame, ass_image_t* img) {
int cnt = 0;
while (img) {
blend_single(frame, img);
++cnt;
img = img->next;
}
printf("%d images blended\n", cnt);
}
int main(int argc, char* argv[]) {
const int frame_w = 640;
const int frame_h = 480;
if (argc < 4) {
printf("usage: %s <image file> <subtitle file> <time>\n", argv[0]);
exit(1);
}
char* imgfile = argv[1];
char* subfile = argv[2];
double tm = strtod(argv[3], 0);
init(frame_w, frame_h);
ass_track_t* track = ass_read_file(ass_library, subfile, NULL);
ass_image_t* img = ass_render_frame(ass_renderer, track, (int)(tm * 1000), NULL);
image_t* frame = gen_image(frame_w, frame_h);
blend(frame, img);
write_png(imgfile, frame);
return 0;
}
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