node-canvas/src/JPEGStream.h

//
// JPEGStream.h
//

#ifndef __NODE_JPEG_STREAM_H__
#define __NODE_JPEG_STREAM_H__

#include "Canvas.h"
#include <jpeglib.h>

/* Expanded data destination object for closure output */
/* inspired by IJG's jdatadst.c */
typedef struct {
  struct jpeg_destination_mgr pub; /* public fields */

  closure_t * closure;
  JOCTET * buffer;
  int bufsize;
} closure_destination_mgr;

void init_closure_destination(j_compress_ptr cinfo){
  // I don't think we really have to do anything here ...
}

boolean empty_closure_output_buffer(j_compress_ptr cinfo){
  closure_destination_mgr * dest = (closure_destination_mgr *) cinfo->dest;
  Local<Buffer> buf = Buffer::New(dest->bufsize);
  memcpy(Buffer::Data(buf->handle_), dest->buffer, dest->bufsize);
  Local<Value> argv[3] = {
    Local<Value>::New(Null()),
    Local<Value>::New(buf->handle_),
    Integer::New(dest->bufsize)
  };
  dest->closure->fn->Call(Context::GetCurrent()->Global(), 3, argv);
  cinfo->dest->next_output_byte = dest->buffer;
  cinfo->dest->free_in_buffer = dest->bufsize;
  return true;
}

void term_closure_destination(j_compress_ptr cinfo){
  closure_destination_mgr * dest = (closure_destination_mgr *) cinfo->dest;
  /* emit remaining data */
  size_t remaining = dest->bufsize - cinfo->dest->free_in_buffer;
  Local<Buffer> buf = Buffer::New(remaining);
  memcpy(Buffer::Data(buf->handle_), dest->buffer, remaining);
  Local<Value> data_argv[3] = {
    Local<Value>::New(Null()),
    Local<Value>::New(buf->handle_),
    Integer::New(remaining)
  };
  dest->closure->fn->Call(Context::GetCurrent()->Global(), 3, data_argv);
  /* emit 'end' */
  Local<Value> end_argv[3] = {
    Local<Value>::New(Null()),
    Local<Value>::New(Null()),
    Integer::New(0)
  };
  dest->closure->fn->Call(Context::GetCurrent()->Global(), 3, end_argv);
}

void jpeg_closure_dest(j_compress_ptr cinfo, closure_t * closure, int bufsize){
  closure_destination_mgr * dest;

  /* The destination object is made permanent so that multiple JPEG images
   * can be written to the same buffer without re-executing jpeg_mem_dest.
   */
  if (cinfo->dest == NULL) {	/* first time for this JPEG object? */
    cinfo->dest = (struct jpeg_destination_mgr *)
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
				  sizeof(closure_destination_mgr));
  }
  
  dest  = (closure_destination_mgr *) cinfo->dest;

  cinfo->dest->init_destination = &init_closure_destination;
  cinfo->dest->empty_output_buffer = &empty_closure_output_buffer;
  cinfo->dest->term_destination = &term_closure_destination;

  dest->closure = closure;
  dest->bufsize = bufsize;
  dest->buffer = (JOCTET *)malloc(bufsize);

  cinfo->dest->next_output_byte = dest->buffer;
  cinfo->dest->free_in_buffer = dest->bufsize;
}

cairo_status_t write_to_jpeg_stream(cairo_surface_t *surface, int bufsize, int quality, closure_t * closure){
  /*
    libjs code adapted from the Cairo R graphics project:
    http://www.rforge.net/Cairo/
  */
  int w = cairo_image_surface_get_width(surface);
  int h = cairo_image_surface_get_height(surface);
	struct jpeg_compress_struct cinfo;
	struct jpeg_error_mgr jerr;

	JSAMPROW slr;
	cinfo.err = jpeg_std_error(&jerr);
	jpeg_create_compress(&cinfo);
	cinfo.in_color_space = JCS_RGB;
	cinfo.input_components = 3;
	cinfo.image_width = w;
	cinfo.image_height = h;
	jpeg_set_defaults(&cinfo);
  /* TODO: quality */
	jpeg_set_quality(&cinfo, quality, (quality<25)?0:1);
  jpeg_closure_dest(&cinfo, closure, bufsize);

	jpeg_start_compress(&cinfo, TRUE);
  unsigned char *dst;
  unsigned int *src = (unsigned int*)cairo_image_surface_get_data(surface);
  int sl = 0;
  dst = (unsigned char*) malloc(w*3);
  while (sl<h) {
    unsigned char *dp = dst;
    int x = 0;
    while (x < w) {
      dp[0] = (*src >> 16) & 255;
      dp[1] = (*src >> 8) & 255;
      dp[2] = *src & 255;
      src++;
      dp += 3;
      x++;
    }
    slr = dst;
    jpeg_write_scanlines(&cinfo, &slr, 1);
    sl++;
  }
  free(dst);
	jpeg_finish_compress(&cinfo);
	jpeg_destroy_compress(&cinfo);
  return CAIRO_STATUS_SUCCESS;
}

#endif