Re: GdkBitmap from black & white .png file

2009-02-05 Thread Richard Shann 
On Thu, 2009-02-05 at 16:20 +, gtk-app-devel-list-requ...@gnome.org
wrote:

> There are functions to convert a PNG with transparency (alpha component)
> to a GdkBitmap according to a threshold. See
> gdk_pixbuf_render_threshold_alpha()
> http://library.gnome.org/devel/gdk/stable/gdk-Pixbufs.html#gdk-pixbuf-render-threshold-alpha
> 
Thank you for this - I have now taken the this approach - adding an
alpha channel to a pixbuf created from the .png and then going to xbm
format and finally to the GdkBitmap.

Richard Shann

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Re: GdkBitmap from black & white .png file

2009-02-05 Thread Yann Droneaud 
Le samedi 31 janvier 2009 à 20:11 +, Richard Shann a écrit :
> The Gdk functions to create bitmaps from data require xbm or xpm data. 
> (For example gdk_bitmap_create_from_data ()). Why do I not see anything
> to create a bitmap from a (b&w) .png image?

There are functions to convert a PNG with transparency (alpha component)
to a GdkBitmap according to a threshold. See
gdk_pixbuf_render_threshold_alpha()
http://library.gnome.org/devel/gdk/stable/gdk-Pixbufs.html#gdk-pixbuf-render-threshold-alpha

BTW, here is a function (not tested) adapted from some code I wrote,
which should create a GdkBitmap from a GdkPixbuf according to your black
and white PNG.
Feel free to test and fix it.

/*
 * Author: Yann Droneaud 
 *
 */
GdkBitmap *
my_gdk_bitmap_new_from_pixbuf_non_alpha(GdkDrawable *drawable, 
GdkPixbuf *pixbuf)
{
 int width;
 int height;
 int rowstride;
 guchar *pixels;
 guint32 pixel;

 gchar *bitmap_data;
 int bitmap_rowstride;
 GdkBitmap *bitmap;

 g_assert(pixbuf != NULL);
 g_assert(gdk_pixbuf_get_colorspace(pixbuf) == GDK_COLORSPACE_RGB);
 g_assert(gdk_pixbuf_get_bits_per_sample(pixbuf) == 8);
 g_assert(gdk_pixbuf_get_has_alpha(pixbuf));
 g_assert(gdk_pixbuf_get_n_channels(pixbuf) == 4);

 width = gdk_pixbuf_get_width(pixbuf);
 height = gdk_pixbuf_get_height(pixbuf);
 rowstride = gdk_pixbuf_get_rowstride(pixbuf);
 pixels = gdk_pixbuf_get_pixels(pixbuf);

 /* round to byte boundary */
 bitmap_rowbytes = (width + 7) / 8;

 /* allocate a *cleared* buffer for the bitmap data */
 bitmap_data = (gchar *) g_malloc0(bitmap_rowbytes * height);
 g_assert(bitmap_data != NULL);

 for(y = 0; y < height; y++) {
   for(x = 0; x < width; x++) {

  /* WARNING: use 4 components, 8 bits per component */
  pixel = * (guint32 *) &pixels[(y * rowbytes) + (x * 4)];

  /* remove alpha component
   * WARNING: beware of endianess 
   */
  pixel &= (guint32) 0xff00UL; 

  /* if not black, it should be white */
  if (pixel != (guint32)0UL) {
bitmap_data[(y * bitmap_rowbytes) + (x / 8)] |= 1 << (x % 8);
  }
   }
 }

 bitmap = gdk_bitmap_create_from_data(drawable, bitmap_data, width, height);

 g_free(bitmap_data);

 return bitmap;
}


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GdkBitmap from black & white .png file

2009-01-31 Thread Richard Shann 
The Gdk functions to create bitmaps from data require xbm or xpm data. 
(For example gdk_bitmap_create_from_data ()). Why do I not see anything
to create a bitmap from a (b&w) .png image?
I've used the pixbuf library before, using gdk_draw_pixbuf() but the
program I am working on uses  a GdkBitmap * mask to draw in the
following fashion:

  gdk_gc_set_clip_mask (gc, mask);
  gdk_gc_set_clip_origin (gc, x, y);
  gdk_draw_rectangle (pixmap, gc, TRUE, x, y, width, height);
  gdk_gc_set_clip_mask (gc, NULL);  /* Removes clip mask */

I don't understand the issues here; I want the application to let the
user select a (small) rectangular area in the .png image for use in as
the GdkBitmap *mask in the above code.

Anyone with a wider view on this stuff? Help would be much appreciated!

Richard Shann


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