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Re: SVG support(again) ?

From: joakim
Subject: Re: SVG support(again) ?
Date: Sat, 18 Aug 2007 13:44:57 +0200
User-agent: Gnus/5.110006 (No Gnus v0.6) Emacs/22.1.50 (gnu/linux)

Richard Stallman <address@hidden> writes:

>     /* Structure describing the image type `svg'.  */
>     static struct image_type svg_type =
>     {
>       &Qsvg,
>       svg_image_p,
>       svg_load,
>       x_clear_image,
>       NULL
>     };
> How about adding another comment for each field explaining what
> the field means and why this particular value is used.
>     /* DEF_IMGLIB_FN() here? */
> I don't understand that comment -- if you do, could you make
> it less terse, and clear?
>     /* helper function for svg_load, does the actual loading
>      given contents and size, apart from frame and image structures, passed 
> from svg_load
>      Uses librsvg to do most of the image processing.
>      Returns non-zero when sucessful
>     */
> That is terse and cryptic.  Could you rewrite it to be clear
> and format it the way we like to do?
> The code of svg_load_image needs more comments explaining what the
> parts of the code do.

Here is a new try. I believe this is quite readable now.
Note that some of the difficulty in understanding this code comes from
reading it in isolation from the other code im image.c. I tried
adding some helpful pointers to other emacs code.


#if defined (HAVE_RSVG)

/* Function prototypes.  */

static int svg_image_p P_ ((Lisp_Object object));
static int svg_load P_ ((struct frame *f, struct image *img));

static int svg_load_image P_ ((struct frame *, struct image *,
                               unsigned char *, unsigned int));

/* The symbol `svg' identifying images of this type. */

Lisp_Object Qsvg;

/* Indices of image specification fields in svg_format, below.  */

enum svg_keyword_index

/* Vector of image_keyword structures describing the format
   of valid user-defined image specifications.  */

static struct image_keyword svg_format[SVG_LAST] =
  {":type",             IMAGE_SYMBOL_VALUE,                     1},
  {":data",             IMAGE_STRING_VALUE,                     0},
  {":file",             IMAGE_STRING_VALUE,                     0},
  {":ascent",           IMAGE_ASCENT_VALUE,                     0},
  {":margin",           IMAGE_POSITIVE_INTEGER_VALUE_OR_PAIR,   0},
  {":relief",           IMAGE_INTEGER_VALUE,                    0},
  {":conversion",       IMAGE_DONT_CHECK_VALUE_TYPE,            0},
  {":heuristic-mask",   IMAGE_DONT_CHECK_VALUE_TYPE,            0},
  {":mask",             IMAGE_DONT_CHECK_VALUE_TYPE,            0},
  {":background",       IMAGE_STRING_OR_NIL_VALUE,              0}

/* Structure describing the image type `svg'.  Its the same type of
   structure defined for all image formats, handled by emacs image functions.
   see struct image_type in dispextern.h

static struct image_type svg_type =
  &Qsvg, /* an identifier showing that this is an image structure for the SVG 
  svg_image_p, /* handle to a function that can be used to identify a svg file*/
  svg_load, /* handle to function used to load a svg file*/
  x_clear_image,/* handle to function to free sresources for SVG*/
  NULL /* an internal field to link to the next image type in a list of image 
types, will be filled in when registering the format*/

/* Return non-zero if OBJECT is a valid SVG image specification.
   do this by calling parse_image_spec and supplying the keywords that identify 
the SVG format

static int
svg_image_p (object)
     Lisp_Object object;
  struct image_keyword fmt[SVG_LAST];
  bcopy (svg_format, fmt, sizeof fmt);

  if (!parse_image_spec (object, fmt, SVG_LAST, Qsvg))
    return 0;

  /* Must specify either the :data or :file keyword.  */
  return fmt[SVG_FILE].count + fmt[SVG_DATA].count == 1;

#include <librsvg/rsvg.h>

/* DEF_IMGLIB_FN() here in the future.
this macro is used to handle loading of dynamic link library functions for 
various OS:es.
currently only librsvg2 is supportedd, which is only available for X, so its 
not strictly necessary yet.
The current code is thought to be compatible with this scheme because of the 
defines below, should librsvg2 become available on more plattforms.

#define fn_rsvg_handle_new              rsvg_handle_new
#define fn_rsvg_handle_set_size_callback rsvg_handle_set_size_callback
#define fn_rsvg_handle_write            rsvg_handle_write
#define fn_rsvg_handle_close            rsvg_handle_close
#define fn_rsvg_handle_get_pixbuf       rsvg_handle_get_pixbuf
#define fn_rsvg_handle_free             rsvg_handle_free

#define fn_gdk_pixbuf_get_width         gdk_pixbuf_get_width
#define fn_gdk_pixbuf_get_height        gdk_pixbuf_get_height
#define fn_gdk_pixbuf_get_pixels        gdk_pixbuf_get_pixels
#define fn_gdk_pixbuf_get_rowstride     gdk_pixbuf_get_rowstride
#define fn_gdk_pixbuf_get_colorspace    gdk_pixbuf_get_colorspace
#define fn_gdk_pixbuf_get_n_channels    gdk_pixbuf_get_n_channels
#define fn_gdk_pixbuf_get_has_alpha     gdk_pixbuf_get_has_alpha
#define fn_gdk_pixbuf_get_bits_per_sample gdk_pixbuf_get_bits_per_sample

/* Load SVG image IMG for use on frame F.  Value is non-zero if
   successful. this function wil go into the svg_type structure, and
   the prototype thus needs to be compatible with that structure */

static int
svg_load (f, img)
     struct frame *f;
     struct image *img;
  int success_p = 0;
  Lisp_Object file_name;

  /* If IMG->spec specifies a file name, create a non-file spec from it.  */
  file_name = image_spec_value (img->spec, QCfile, NULL);
  if (STRINGP (file_name))
      Lisp_Object file;
      unsigned char *contents;
      int size;
      struct gcpro gcpro1;

      file = x_find_image_file (file_name);
      GCPRO1 (file);
      if (!STRINGP (file))
        image_error ("Cannot find image file `%s'", file_name, Qnil);
        return 0;

      contents = slurp_file (SDATA (file), &size); /* read the entire file into 
      if (contents == NULL)
        image_error ("Error loading SVG image `%s'", img->spec, Qnil);
        return 0;

      success_p = svg_load_image (f, img, contents, size); /* if the file was 
slurped into memory properly, parse it*/
      xfree (contents);
  else/*its not a file, its a lisp object*/
      Lisp_Object data;

      data = image_spec_value (img->spec, QCdata, NULL);
      success_p = svg_load_image (f, img, SDATA (data), SBYTES (data));

  return success_p;

/* helper function for svg_load, does the actual loading
 given contents and size, apart from frame and image structures, passed from 

 Uses librsvg to do most of the image processing.
 Returns non-zero when sucessful
static int
svg_load_image (f, img, contents, size)
     struct frame *f;
     struct image *img;
     unsigned char *contents;
     unsigned int size;
  RsvgHandle *rsvg_handle;
  GError *error = NULL;
  GdkPixbuf *pixbuf;
  int width;
  int height;
  const guint8 *pixels;
  int rowstride;
  XImagePtr ximg;
  XColor background;
  int x;
  int y;

  g_type_init (); /*glib function that must be called prior to using gnome type 
library functions*/
  rsvg_handle = fn_rsvg_handle_new ();/* make a handle to a new rsvg object*/

  fn_rsvg_handle_write (rsvg_handle, contents, size, &error);/*parse "contents" 
and fill in the rsvg_handle*/
  if (error)
    goto rsvg_error;

  fn_rsvg_handle_close (rsvg_handle, &error);/*the parsing is complete, 
rsvg_handle is ready to use*/
  if (error)
    goto rsvg_error;

  pixbuf = fn_rsvg_handle_get_pixbuf (rsvg_handle);/* we can now get a valid 
pixel buffer from the svg file, if all went ok*/
  eassert (pixbuf);

  /* extract some meta data from he svg handle*/
  width     = fn_gdk_pixbuf_get_width (pixbuf);
  height    = fn_gdk_pixbuf_get_height (pixbuf);
  pixels    = fn_gdk_pixbuf_get_pixels (pixbuf);
  rowstride = fn_gdk_pixbuf_get_rowstride (pixbuf);

  /*validate the svg meta data*/
  eassert (fn_gdk_pixbuf_get_colorspace (pixbuf) == GDK_COLORSPACE_RGB);
  eassert (fn_gdk_pixbuf_get_n_channels (pixbuf) == 4);
  eassert (fn_gdk_pixbuf_get_has_alpha (pixbuf));
  eassert (fn_gdk_pixbuf_get_bits_per_sample (pixbuf) == 8);

  /* try to create a x pixmap to hold the svg pixmap*/
  if (!x_create_x_image_and_pixmap (f, width, height, 0, &ximg, &img->pixmap)) {
    g_object_unref (pixbuf);
    return 0;

  init_color_table ();


  background.pixel = FRAME_BACKGROUND_PIXEL (f);
  x_query_color (f, &background);

  /* svg pixmaps specify transparency in the last byte, so right shift 8 bits 
to get rid of it, since emacs doesnt support transparency*/
  background.red   >>= 8;
  background.green >>= 8;
  background.blue  >>= 8;

#else /* not HAVE_X_WINDOWS */
#error FIXME

  /* this loop handles opacity values, since emacs assumes
     non-transparent images.  Each pixel must be "flattened" by
     calculating he resulting color, given the transparency of the
     pixel, and the image background color.
  for (y = 0; y < height; ++y)
      for (x = 0; x < width; ++x)
          unsigned red;
          unsigned green;
          unsigned blue;
          unsigned opacity;

          red     = *pixels++;
          green   = *pixels++;
          blue    = *pixels++;
          opacity = *pixels++;

          red   = ((red * opacity)
                   + (background.red * ((1 << 8) - opacity)));
          green = ((green * opacity)
                   + (background.green * ((1 << 8) - opacity)));
          blue  = ((blue * opacity)
                   + (background.blue * ((1 << 8) - opacity)));

          XPutPixel (ximg, x, y, lookup_rgb_color (f, red, green, blue));

      pixels += rowstride - 4 * width;

  /* Remember colors allocated for this image.  */
  img->colors = colors_in_color_table (&img->ncolors);
  free_color_table ();

  g_object_unref (pixbuf);

  /* Put the image into the pixmap, then free the X image and its buffer. */
  x_put_x_image (f, ximg, img->pixmap, width, height);
  x_destroy_x_image (ximg);

  img->width  = width;
  img->height = height;

  return 1;

  /* FIXME: Use error->message. */
  image_error ("Error parsing SVG image `%s'", img->spec, Qnil);
  g_error_free (error);
  return 0;

#endif  /* defined (HAVE_RSVG) */

Joakim Verona

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