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190 lines
5.9 KiB
C
190 lines
5.9 KiB
C
/*
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This source is published under the following 3-clause BSD license.
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Copyright (c) 2012, Lukas Hosek and Alexander Wilkie
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All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:
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* Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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* None of the names of the contributors may be used to endorse or promote
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products derived from this software without specific prior written
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permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY
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DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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/* ============================================================================
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This file is part of a sample implementation of the analytical skylight model
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presented in the SIGGRAPH 2012 paper
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"An Analytic Model for Full Spectral Sky-Dome Radiance"
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by
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Lukas Hosek and Alexander Wilkie
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Charles University in Prague, Czech Republic
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Version: 1.0, May 11th, 2012
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Please visit http://cgg.mff.cuni.cz/projects/SkylightModelling/ to check if
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an updated version of this code has been published!
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============================================================================ */
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/*
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This code is taken from ART, a rendering research system written in a
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mix of C99 / Objective C. Since ART is not a small system and is intended to
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be inter-operable with other libraries, and since C does not have namespaces,
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the structures and functions in ART all have to have the somewhat wordy
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canonical names that begin with Ar.../ar..., like those seen in this example.
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Usage information:
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==================
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Model initialisation
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--------------------
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A separate ArHosekSkyModelState has to be maintained for each spectral
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band you want to use the model for. So in a renderer with num_channels
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bands, you would need something like
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ArHosekSkyModelState * skymodel_state[num_channels];
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You then have to allocate these states. In the following code snippet, we
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assume that "albedo" is defined as
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double albedo[num_channels];
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with a ground albedo value between [0,1] for each channel. The solar elevation
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is given in radians.
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for ( unsigned int i = 0; i < num_channels; i++ )
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skymodel_state[i] =
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arhosekskymodelstate_alloc_init(
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turbidity,
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albedo[i],
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solarElevation
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);
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Using the model to generate skydome samples
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-------------------------------------------
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Generating a skydome radiance spectrum "skydome_result" for a given location
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on the skydome determined via the angles theta and gamma works as follows:
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double skydome_result[num_channels];
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for ( unsigned int i = 0; i < num_channels; i++ )
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skydome_result[i] =
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arhosekskymodel_radiance(
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skymodel_state[i],
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theta,
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gamma,
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channel_center[i]
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);
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The variable "channel_center" is assumed to hold the channel center wavelengths
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for each of the num_channels samples of the spectrum we are building.
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Cleanup after use
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-----------------
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After rendering is complete, the content of the sky model states should be
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disposed of via
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for ( unsigned int i = 0; i < num_channels; i++ )
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arhosekskymodelstate_free( skymodel_state[i] );
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CIE XYZ Version of the Model
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----------------------------
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Usage of the CIE XYZ version of the model is exactly the same, except that
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num_channels is of course always 3, and that ArHosekXYZSkyModelState and
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arhosek_xyz_skymodel_radiance() have to be used instead of their spectral
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counterparts.
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*/
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typedef double ArHosekSkyModelConfiguration[9];
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// Spectral version of the model
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typedef struct ArHosekSkyModelState
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{
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ArHosekSkyModelConfiguration configs[11];
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double radiances[11];
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}
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ArHosekSkyModelState;
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ArHosekSkyModelState * arhosekskymodelstate_alloc_init(
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const double turbidity,
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const double albedo,
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const double elevation
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);
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void arhosekskymodelstate_free(
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ArHosekSkyModelState * state
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);
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double arhosekskymodel_radiance(
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ArHosekSkyModelState * state,
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double theta,
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double gamma,
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double wavelength
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);
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// CIE XYZ version
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typedef struct ArHosekXYZSkyModelState
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{
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ArHosekSkyModelConfiguration configs[3];
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double radiances[3];
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}
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ArHosekXYZSkyModelState;
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ArHosekXYZSkyModelState * arhosek_xyz_skymodelstate_alloc_init(
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const double turbidity,
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const double albedo,
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const double elevation
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);
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void arhosek_xyz_skymodelstate_free(
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ArHosekXYZSkyModelState * state
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);
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double arhosek_xyz_skymodel_radiance(
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ArHosekXYZSkyModelState * state,
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double theta,
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double gamma,
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int channel
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); |