source: downloads/ogre/OgreMain/src/OgreShadowCameraSetup.cpp @ 48

/*
-----------------------------------------------------------------------------
This source file is part of OGRE
(Object-oriented Graphics Rendering Engine)
For the latest info, see http://www.ogre3d.org/

Copyright (c) 2006  Torus Knot Software Ltd
Also see acknowledgements in Readme.html

This program 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 of the License, or (at your option) any later
version.

This program 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
this program; if not, write to the Free Software Foundation, Inc., 59 Temple
Place - Suite 330, Boston, MA 02111-1307, USA, or go to
http://www.gnu.org/copyleft/lesser.txt.

You may alternatively use this source under the terms of a specific version of
the OGRE Unrestricted License provided you have obtained such a license from
Torus Knot Software Ltd.
-----------------------------------------------------------------------------
*/

#include "OgreStableHeaders.h"
#include "OgreCommon.h"
#include "OgreSceneManager.h"
#include "OgreLight.h"
#include "OgreShadowCameraSetup.h"
#include "OgreCamera.h"
#include "OgreViewport.h"


namespace Ogre 
{
        /// Default constructor
        DefaultShadowCameraSetup::DefaultShadowCameraSetup()  {}
        
        /// Destructor
        DefaultShadowCameraSetup::~DefaultShadowCameraSetup() {}
        
        /// Default shadow camera setup implementation
        void DefaultShadowCameraSetup::getShadowCamera (const SceneManager *sm, const Camera *cam, 
                const Viewport *vp, const Light *light, Camera *texCam) const
        {
                Vector3 pos, dir;

                // reset custom view / projection matrix in case already set
                texCam->setCustomViewMatrix(false);
                texCam->setCustomProjectionMatrix(false);

                // get the shadow frustum's far distance
                Real shadowDist = sm->getShadowFarDistance();
                if (!shadowDist)
                {
                        // need a shadow distance, make one up
                        shadowDist = cam->getNearClipDistance() * 300;
                }
                Real shadowOffset = shadowDist * (sm->getShadowDirLightTextureOffset());

                // Directional lights 
                if (light->getType() == Light::LT_DIRECTIONAL)
                {
                        // set up the shadow texture
                        // Set ortho projection
                        texCam->setProjectionType(PT_ORTHOGRAPHIC);
                        // set easy FOV and near dist so that texture covers far dist
                        texCam->setFOVy(Degree(90));
                        texCam->setNearClipDistance(shadowDist);

                        // Calculate look at position
                        // We want to look at a spot shadowOffset away from near plane
                        // 0.5 is a litle too close for angles
                        Vector3 target = cam->getDerivedPosition() + 
                                (cam->getDerivedDirection() * shadowOffset);

                        // Calculate direction, which same as directional light direction
                        dir = - light->getDerivedDirection(); // backwards since point down -z
                        dir.normalise();

                        // Calculate position
                        // We want to be in the -ve direction of the light direction
                        // far enough to project for the dir light extrusion distance
                        pos = target + dir * sm->getShadowDirectionalLightExtrusionDistance();

                        // Round local x/y position based on a world-space texel; this helps to reduce
                        // jittering caused by the projection moving with the camera
                        // Viewport is 2 * near clip distance across (90 degree fov)
                        Real worldTexelSize = (texCam->getNearClipDistance() * 20) / vp->getActualWidth();
                        pos.x -= fmod(pos.x, worldTexelSize);
                        pos.y -= fmod(pos.y, worldTexelSize);
                        pos.z -= fmod(pos.z, worldTexelSize);
                }
                // Spotlight
                else if (light->getType() == Light::LT_SPOTLIGHT)
                {
                        // Set perspective projection
                        texCam->setProjectionType(PT_PERSPECTIVE);
                        // set FOV slightly larger than the spotlight range to ensure coverage
                        texCam->setFOVy(light->getSpotlightOuterAngle()*1.2);
                        // set near clip the same as main camera, since they are likely
                        // to both reflect the nature of the scene
                        texCam->setNearClipDistance(cam->getNearClipDistance());

                        // Calculate position, which same as spotlight position
                        pos = light->getDerivedPosition();

                        // Calculate direction, which same as spotlight direction
                        dir = - light->getDerivedDirection(); // backwards since point down -z
                        dir.normalise();
                }
                // Point light
                else
                {
                        // Set perspective projection
                        texCam->setProjectionType(PT_PERSPECTIVE);
                        // Use 120 degree FOV for point light to ensure coverage more area
                        texCam->setFOVy(Degree(120));
                        // set near clip the same as main camera, since they are likely
                        // to both reflect the nature of the scene
                        texCam->setNearClipDistance(cam->getNearClipDistance());

                        // Calculate look at position
                        // We want to look at a spot shadowOffset away from near plane
                        // 0.5 is a litle too close for angles
                        Vector3 target = cam->getDerivedPosition() + 
                                (cam->getDerivedDirection() * shadowOffset);

                        // Calculate position, which same as point light position
                        pos = light->getDerivedPosition();

                        dir = (pos - target); // backwards since point down -z
                        dir.normalise();
                }

                // Finally set position
                texCam->setPosition(pos);

                // Calculate orientation based on direction calculated above
                /*
                // Next section (camera oriented shadow map) abandoned
                // Always point in the same direction, if we don't do this then
                // we get 'shadow swimming' as camera rotates
                // As it is, we get swimming on moving but this is less noticeable

                // calculate up vector, we want it aligned with cam direction
                Vector3 up = cam->getDerivedDirection();
                // Check it's not coincident with dir
                if (up.dotProduct(dir) >= 1.0f)
                {
                // Use camera up
                up = cam->getUp();
                }
                */
                Vector3 up = Vector3::UNIT_Y;
                // Check it's not coincident with dir
                if (Math::Abs(up.dotProduct(dir)) >= 1.0f)
                {
                        // Use camera up
                        up = Vector3::UNIT_Z;
                }
                // cross twice to rederive, only direction is unaltered
                Vector3 left = dir.crossProduct(up);
                left.normalise();
                up = dir.crossProduct(left);
                up.normalise();
                // Derive quaternion from axes
                Quaternion q;
                q.FromAxes(left, up, dir);
                texCam->setOrientation(q);
        }


}