[Gegl-developer] Proposition : GeglInterpolator

[Geert Jordaens]

Daniel Rogers wrote:
> On Wed, 2006-10-11 at 21:33 +0200, Geert Jordaens wrote:
>   
>> In order not to rewrite interpolation fnctionality for every operation I 
>> would like to propose following API.
>>
>> GeglInterpolator
>>  +- GeglInterpolatorLinear
>>  | 
>>  + GeglInterpolatorCubic
>>  | 
>>  + GeglInterpolatorLanczos
>>
>> usage :
>>
>> /* first create the interpolator */
>> GeglInterpolatorLinear *interpolator = g_object_new 
>> (GEGL_TYPE_INTERPLATOR_LINEAR,
>>                                                      "source", buffer,
>>                                                      "format", 
>> babl_format ("RaGaBaA float"),
>>                                                      NULL);
>>
>>
>> gegl_interpolator_prepare(interpolator); /* prepares a linear buffer in 
>> the format suitable for the interpolation routine. */
>>
>> gegl_interpolator_get(interpolator, x, y, dst); /* returns a 
>> interpolated pixel in dst */
>>     
>
> sllooooooooooow.  I've encountered this oh-so-wonderful abstraction
> before (JAI uses it, among others). Making a method call in the inner
> loop of your pixel calculation routine is a big-nono.  The first
> optimization you will make is to remove that.  Typically, the common
> case will not use the abstraction, and an operator will be provided that
> can accept the general interpolation object, but the operator will be so
> slow no one will use it.  It is wonderful when developing your
> foundations, to be sure, but it will eventually be ripped out as soon as
> someone tries to speed it up.
>
> If you can provide versions that accept arrays as input, then the
> general case can be used everywhere.  Actually that can be made a
> general rule.  Anything that manipulates pixels much accept arrays as
> input (possibly masks as well) or they will be ripped out at the
> earliest opportunity.
>
>   
If i understand it correctly it is the GObject that is causing the slowdown?

I don't see any difference with the pixel_iterator in Gimp.

In your last paragraph, i assume you mean writing a function that can be 
used on a linear buffer :

interpolate_buffer_linear ( srcbuf, x0, y0,  width, height, x, y, destbuf );
srcbuf = linear source buffer (array)
x0,y0 = integer origin
width, height  = integer size of buffer
x,y = double position to be interpolated.
destbuf = destination pixel.

Then it is up to the operation to make sure the srcbuf/dstbuf is in a 
suitable format?