1 // dir_lights.hxx -- build a 'directional' light on the fly
3 // Written by Curtis Olson, started March 2002.
5 // Copyright (C) 2002 Curtis L. Olson - curt@flightgear.org
7 // This program is free software; you can redistribute it and/or
8 // modify it under the terms of the GNU General Public License as
9 // published by the Free Software Foundation; either version 2 of the
10 // License, or (at your option) any later version.
12 // This program is distributed in the hope that it will be useful, but
13 // WITHOUT ANY WARRANTY; without even the implied warranty of
14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 // General Public License for more details.
17 // You should have received a copy of the GNU General Public License
18 // along with this program; if not, write to the Free Software
19 // Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
24 #ifndef _DIR_LIGHTS_HXX
25 #define _DIR_LIGHTS_HXX
29 # error This library requires C++
37 #include <simgear/compiler.h>
41 #include <plib/ssg.h> // plib include
46 // Define the various supported light types
51 FG_RWYLIGHT_TOUCHDOWN,
52 FG_RWYLIGHT_THRESHOLD,
60 // Generate a directional light. This routines creates a
61 // 'directional' light that can only be viewed from within 90 degrees
62 // of the specified dir vector.
64 // To accomplish this, he routine creates a triangle with the 1st
65 // point coincident with the specified pt and the 2nd and 3rd points
66 // extending upward. The 1st point is created with an 'alpha' value
67 // of 1 while the 2nd and 3rd points are created with an 'alpha' of
70 // If the triangle is drawn in glPolygonMode(GL_FRONT, GL_POINT) mode,
71 // then two important things happen:
73 // 1) Only the 3 vertex points are drawn, the 2nd two with an alpha of
74 // 0 so actually only the desired point is rendered.
76 // 2) since we are drawing a triangle, back face culling takes care of
77 // eliminating this poing when the view angle relative to dir is
78 // greater than 90 degrees.
80 // The final piece of this puzzle is that if we now use environment
81 // mapping on this point, via an appropriate texture we can then
82 // control the intensity and color of the point based on the view
83 // angle relative to 'dir' the optimal view direction of the light
84 // (i.e. the direction the light is pointing.)
86 // Yes this get's to be long and convoluted. If you can suggest a
87 // simpler way, please do! :-)
89 ssgLeaf *gen_directional_light( sgVec3 pt, sgVec3 dir );
92 #endif // _DIR_LIGHTS_HXX