Integrate skylight model. Work in progress.

extern/skylight/ArHosekSkyModel.h

@@ -0,0 +1,190 @@
+/*
+This source is published under the following 3-clause BSD license.
+
+Copyright (c) 2012, Lukas Hosek and Alexander Wilkie
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without 
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * 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.
+    * None of the names of the contributors may be used to endorse or promote 
+      products derived from this software without specific prior written 
+      permission.
+
+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 HOLDERS 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.
+*/
+
+
+/* ============================================================================
+
+This file is part of a sample implementation of the analytical skylight model
+presented in the SIGGRAPH 2012 paper
+
+
+           "An Analytic Model for Full Spectral Sky-Dome Radiance"
+
+                                    by 
+
+                       Lukas Hosek and Alexander Wilkie
+                Charles University in Prague, Czech Republic
+
+
+                        Version: 1.0, May 11th, 2012
+
+
+Please visit http://cgg.mff.cuni.cz/projects/SkylightModelling/ to check if
+an updated version of this code has been published!
+
+============================================================================ */
+
+
+/*
+
+This code is taken from ART, a rendering research system written in a
+mix of C99 / Objective C. Since ART is not a small system and is intended to 
+be inter-operable with other libraries, and since C does not have namespaces, 
+the structures and functions in ART all have to have the somewhat wordy 
+canonical names that begin with Ar.../ar..., like those seen in this example.
+
+Usage information:
+==================
+
+
+Model initialisation
+--------------------
+
+A separate ArHosekSkyModelState has to be maintained for each spectral
+band you want to use the model for. So in a renderer with num_channels
+bands, you would need something like
+
+    ArHosekSkyModelState  * skymodel_state[num_channels];
+
+You then have to allocate these states. In the following code snippet, we
+assume that "albedo" is defined as
+
+    double  albedo[num_channels];
+
+with a ground albedo value between [0,1] for each channel. The solar elevation  
+is given in radians.
+
+    for ( unsigned int i = 0; i < num_channels; i++ )
+        skymodel_state[i] =
+            arhosekskymodelstate_alloc_init(
+                  turbidity,
+                  albedo[i],
+                  solarElevation
+                );
+
+
+Using the model to generate skydome samples
+-------------------------------------------
+
+Generating a skydome radiance spectrum "skydome_result" for a given location
+on the skydome determined via the angles theta and gamma works as follows:
+
+    double  skydome_result[num_channels];
+
+    for ( unsigned int i = 0; i < num_channels; i++ )
+        skydome_result[i] =
+            arhosekskymodel_radiance(
+                skymodel_state[i],
+                theta,
+                gamma,
+                channel_center[i]
+              );
+              
+The variable "channel_center" is assumed to hold the channel center wavelengths
+for each of the num_channels samples of the spectrum we are building.
+
+
+Cleanup after use
+-----------------
+
+After rendering is complete, the content of the sky model states should be
+disposed of via
+
+        for ( unsigned int i = 0; i < num_channels; i++ )
+            arhosekskymodelstate_free( skymodel_state[i] );
+
+
+CIE XYZ Version of the Model
+----------------------------
+
+Usage of the CIE XYZ version of the model is exactly the same, except that
+num_channels is of course always 3, and that ArHosekXYZSkyModelState and
+arhosek_xyz_skymodel_radiance() have to be used instead of their spectral
+counterparts.
+
+*/
+
+typedef double ArHosekSkyModelConfiguration[9];
+
+
+// Spectral version of the model
+
+
+typedef struct ArHosekSkyModelState
+{
+    ArHosekSkyModelConfiguration  configs[11];
+    double                        radiances[11];
+} 
+ArHosekSkyModelState;
+
+ArHosekSkyModelState  * arhosekskymodelstate_alloc_init(
+        const double  turbidity, 
+        const double  albedo, 
+        const double  elevation
+        );
+
+void arhosekskymodelstate_free(
+        ArHosekSkyModelState  * state
+        );
+
+double arhosekskymodel_radiance(
+        ArHosekSkyModelState  * state,
+        double                  theta, 
+        double                  gamma, 
+        double                  wavelength
+        );
+
+
+// CIE XYZ version
+
+
+typedef struct ArHosekXYZSkyModelState
+{
+    ArHosekSkyModelConfiguration  configs[3];
+    double                        radiances[3];
+} 
+ArHosekXYZSkyModelState;
+
+ArHosekXYZSkyModelState  * arhosek_xyz_skymodelstate_alloc_init(
+        const double  turbidity, 
+        const double  albedo, 
+        const double  elevation
+        );
+
+void arhosek_xyz_skymodelstate_free(
+        ArHosekXYZSkyModelState * state
+        );
+
+double arhosek_xyz_skymodel_radiance(
+        ArHosekXYZSkyModelState * state,
+        double                  theta, 
+        double                  gamma, 
+        int                     channel
+        );