> Zoltan Phelps wrote: > > >> > >> On 16 Mar 2008, at 22:31, Zoltan Phelps wrote: > >> > >> > I searched the forum but didn't find any suitable thread. > >> > In my application i would like to show two images, one "original" > >> > version and one "altered" version (e.g. after LUT conversion). > >> > My question is - how can i access the pixel data of an Fl_RGB_Image > >> > directly? The source code reveals only the "const char * const *data > >> > ();" member function but as it is constant i'm not able to change > >> > anything. Is there another suitable way? Or is it better to just > >> > keep an unsigned char array with the pixel data, change it as > >> > desired and redraw it with the fl_draw_image function without > >> > creating any Fl_()_Image object? I'm a bit confused because with > >> > different libraries i used to create an image object and to alter > >> > its pixel data there had always been an access member function. > >> > Thanks in advance! > >> > >> http://www.fltk.org/articles.php?L466 > >> > >> http://www.fltk.org/articles.php?L468 > >> > >> > >> > > > > Hey, these two links are a great help! Thanks a lot, that was what i've > > been looking for. > > Just a tip. Fl_Image::data() returns an _array_ of image buffers. I've > forgotten this a few times and spent far too long in a debugger trying to > figure out why I was getting segfaults. > > For example, > > Fl_Shared_Image *img = Fl_Shared_Image::get("somepic.png"); > > const char *img_data = img->data(); > > That is wrong if you try to access the pixel values in img_data. Doing so > will eventually segfault. > > The correct way is: > > const char *img_data = img->data()[0]; > > Another tip, after manipulating img_data, use Fl_Image::uncache() before > calling redraw() on the widget. Again, I spent far too long in a debugger > when my changes to img_data were not being displayed. I think this applies > only if you display img before you manipulate the pixels though. > > -- > Alvin
Thanks for the hints, i studied the sources of Fl_Image.* and found that uncache() thing already inside the desaturate() or color_average() functions. That img->data() returns a char array wasn't clear until i read the articles #466 and #468. Since i'm only using the Fl_RGB_Image class i found an easier way by just typing unsigned char * pixels = (unsigned char *) img->array; because array is a public pointer to the pixel data. (Is that good coding style? ;)) ZP _______________________________________________ fltk mailing list [email protected] http://lists.easysw.com/mailman/listinfo/fltk
