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/* Copyright (C) 2007 Claus-Justus Heine
*
* This file is part of Geomview.
*
* Geomview is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published
* by the Free Software Foundation; either version 2, or (at your option)
* any later version.
*
* Geomview is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with Geomview; see the file COPYING. If not, write
* to the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139,
* USA, or visit http://www.gnu.org.
*/
/* Implement Geomview's "apply = blend" for constant shading
*
* Maybe mgrib should set bgalpha to 0 if transparency is not enabled
* (0 because this will leave the alpha channel of the surface
* unaffected).
*
* The additional parameter At interpolates between 1 and Ot; the
* effective alpha contribution from the texture will be (1-At) + At *
* Ot.
*/
surface
GVreplaceconstant(string texturename = "";
float At = 1;)
{
/* texture provided color (luminance) and alpha */
color Ct;
float Ot;
/* number of texture channels,
* < 3: liminance and possibly alpha, > 2: rgb and possibly alpha
*/
float channels;
if (texturename != "" &&
textureinfo(texturename, "channels", channels) == 1.0) {
if (channels < 3) {
Ct = float texture (texturename[0], "width", 0.0);
if (channels == 2) {
Ot = float texture (texturename[1], "width", 0.0);
}
} else {
Ct = color texture (texturename, "width", 0.0);
if (channels == 4) {
Ot = float texture (texturename[3], "width", 0.0);
}
}
Ot = (1.0 - At) + At * Ot;
Ci = Ct * Ot;
Oi = Ot;
} else {
/* no texture: use ordinary constant shader */
Ci = Cs;
Oi = Os;
Ci *= Os;
}
}
/*
* Local Variables: ***
* mode: c ***
* c-basic-offset: 2 ***
* End: ***
*/
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