[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [E-devel] Premultiply or not



	Brian and Nathan write:

> I think we should at least provide a set of functions for
> converting image data / color values between the two spaces.
> ...


> I would also suggest a set of conversion functions for performing
> the premul conversion on non-premul image data. ...
> ...

	Sure, without question :)

	Let me warn everyone who still intends to work using
non-premul data (and/or colors) -- it's tricky to mix these
two color spaces, you may end up getting mixed-up yourself.

	Here's an example of what happens right now in evas
because we're using non-premul data in the software based
engines vs what happens when we use the xrender engine.

	Take the following Simon inspired example:

   Evas_Object  *obj;
   unsigned int data[2] = {0xff00ff00, 0x00ff0000};
//  This gives 2x1 sized image data with "opaque-green"
//  and "transparent-red" pixels.

   obj = evas_object_image_add(some_evas);
   evas_object_image_size_set(obj, 2, 1);
   evas_object_image_data_set(obj, (unsigned int *)data);
   evas_object_iamge_alpha_set(obj, 1);
   evas_object_resize(obj, 100, 100);
   evas_object_image_fill_set(obj, 0, 0, 100, 100);
   evas_object_image_smooth_scale_set(obj, 1);
   evas_object_image_border_set(obj, 0, 0, 0, 0);
   evas_object_move(obj, some_x, some_y);
   evas_object_layer_set(obj, some_layer);
   evas_object_clip_set(obj, some_clip);
   evas_object_show(obj);

	If you display this with the software-x11 engine
(onto a white background say), you will see a 100x100 image
which varies from opaque-green at the left edje to transparent
at the right edje, with some redish and brownish in between.
	However, if you display this with the xrender-x11 engine,
you will see an image varying from opaque-green at the left edje
to transparent at the right edje with no 'redish' or 'brownish'
anywhere.

	I haven't actually checked it with what's in CVS (we've been
making scaling changes lately), but I think that's what will happen.


   jose.