/*  Part of XPCE --- The SWI-Prolog GUI toolkit

    Author:        Jan Wielemaker and Anjo Anjewierden
    E-mail:        jan@swi.psy.uva.nl
    WWW:           http://www.swi.psy.uva.nl/projects/xpce/
    Copyright (c)  2001-2011, University of Amsterdam
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

    1. Redistributions of source code must retain the above copyright
       notice, this list of conditions and the following disclaimer.

    2. Redistributions in binary form must reproduce the above copyright
       notice, this list of conditions and the following disclaimer in
       the documentation and/or other materials provided with the
       distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    POSSIBILITY OF SUCH DAMAGE.
*/

:- module(gradient, []).
:- use_module(library(pce)).

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Class gradient is a subclass of image representing a gradient 1xN or Nx1
image that can be used as fill-pattern. The idea is to define a gradient
as  a  smooth  transition  from  one  colour  to  another.  The  current
implementation is more a prototype, lacking the following optimizations:

        * Don't use to many colours on 256 colour displays
        * Avoid creating a colour for each pixel when making long gradients
        * Allow for different algorithms

The current implementation uses a linear   transition in HSV-space. This
is probably one of  the  sensible   algorithms,  but  possibly we should
provide alternatives.

To create a vertical gradient in (X,Y,W,H), do:

gradient(Device, ColourTop, ColourBottom, X, Y, W, H) :-
        send(Device, display, new(B, box(W,H)), point(X,Y)),
        send(B, pen, 0),
        send(B, fill_offset, point(0,0)),
        send(B, fill,
             gradient(@nil, ColourTop, ColourBottom, H, vertical)).

NOTE: DOS-7 based Windows (Windows 95/98/ME)   has severe limitations on
handling fill-patterns. XPCE has hacks to   avoid  these for rectangles,
making the above code only work for   boxes with <-radius: 0, no shadow,
and <-fill_offset: point(0,0). On X11 and NT   gradients  can be used on
all objects accepting  an  image  as   `colour'  for  its  interior. For
details, see also `box->fill'.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

:- pce_begin_class(gradient, image,
                   "Create a gradient-image for filling").

variable(from,        colour,                get, "Starting colour").
variable(to,          colour,                get, "ending colour").
variable(orientation, {horizontal,vertical}, get, "Direction").


initialise(G,
           Name:name=[name]*,
           From:from=colour, To:to=colour,
           Length:length='0..',
           Orientation:orientation={horizontal,vertical}) :->
    (   Orientation == vertical
    ->  W = 1, H = Length
    ;   H = 1, W = Length
    ),
    send_super(G, initialise, Name, W, H, pixmap),
    send(G, slot, from, From),
    send(G, slot, to, To),
    send(G, slot, orientation, Orientation),
    send(G, update).

:- pce_group(dimension).

length(G, Len:'0..') :<-
    "Get current length"::
    get(G, size, size(W,H)),
    (   get(G, orientation, vertical)
    ->  Len = H
    ;   Len = W
    ).
length(G, Len:'0..') :->
    "Change the length"::
    (   get(G, length, Len)
    ->  true
    ;   (   get(G, orientation, horizontal)
        ->  send(G, resize, Len, 1)
        ;   send(G, resize, 1, Len)
        ),
        send(G, update)
    ).

orientation(G, O:orientation) :->
    "Change the orientation, keeping the other parameters"::
    (   get(G, orientation, O)
    ->  true
    ;   get(G, length, Len),
        (   O == horizontal
        ->  send(G, resize, Len, 1)
        ;   send(G, resize, 1, Len)
        ),
        send(G, slot, orientation, O),
        send(G, update)
    ).


horizontal(G, G2:gradient) :<-
    "Get horizontal version or <-self"::
    (   get(G, orientation, horizontal)
    ->  true
    ;   get(G, clone, G2),
        send(G, orientation, horizontal)
    ).

vertical(G, G2:gradient) :<-
    "Get vertical version or <-self"::
    (   get(G, orientation, vertical)
    ->  true
    ;   get(G, clone, G2),
        send(G, orientation, vertical)
    ).


:- pce_group(fill).

update(G) :->
    "Actually fill using the gradient"::
    get(G, from, From),
    get(G, to, To),
    hsv(From, F),
    hsv(To,   T),
    get(G, length, Len),
    get(G, orientation, Orientation),
    fill_gradient(0, Len, Orientation, G, F, T).

hsv(Colour, hsv(H, S, V)) :-
    get(Colour, hue, H),
    get(Colour, saturnation, S),
    get(Colour, value, V).

fill_gradient(Y, Height, _, _, _, _) :-
    Y >= Height,
    !.
fill_gradient(Y, Height, Orientation, Image, F, T) :-
    F = hsv(HF, SF, VF),
    T = hsv(HT, ST, VT),
    H is round(HF + (HT-HF) * Y/Height),
    S is round(SF + (ST-SF) * Y/Height),
    V is round(VF + (VT-VF) * Y/Height),
    (   Orientation == vertical
    ->  send(Image, pixel, 0, Y, colour(@default, H, S, V, hsv))
    ;   send(Image, pixel, Y, 0, colour(@default, H, S, V, hsv))
    ),
    Y2 is Y + 1,
    fill_gradient(Y2, Height, Orientation, Image, F, T).

:- pce_end_class(gradient).
