/* -*-c++-*- */
/* osgEarth - Geospatial SDK for OpenSceneGraph
* Copyright 2020 Pelican Mapping
* http://osgearth.org
*
* osgEarth 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.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program.  If not, see <http://www.gnu.org/licenses/>
*/
#ifndef OSGEARTH_OVERLAY_CLAMPING_TECHNIQUE
#define OSGEARTH_OVERLAY_CLAMPING_TECHNIQUE

#include <osgEarth/Common>
#include <osgEarth/OverlayDecorator>
#include <osgEarth/Clamping>

#define OSGEARTH_CLAMPING_BIN "osgEarth::ClampingBin"

namespace osgEarth
{
    class TerrainEngineNode;
}

namespace osgEarth { namespace Util
{
    /**
     * Clamps geometry to the terrain using the GPU.
     *
     * This overlay technique installs a shader that samples the depth
     * of the underlying terrain and then adjusts the vertex position to
     * the height of the terrain. It then applies a depth offset in order
     * to mitigate Z-fighting.
     *
     * Approach
     *
     * This technique works by first setting up a nadir-view RTT camera that
     * captures the depth component of the terrain within the view frustum of
     * the main camera. Then the GPU uses this "depth texture" to move each
     * vertex so it coindices with the terrain.
     *
     * Limitations
     *
     * Since this is an orthographic view, the effective resolution of depth
     * data close to the camera may not be quite sufficient, especially when
     * the camera is pitched up looking out over the horizon. As a reuslt, you
     * may see the verts "jitter" slightly in the Z direciton as you camera moves.
     *
     * Performance takes a hit since we need to RTT the terrain in a pre-render
     * pass.
     */
    class OSGEARTH_EXPORT ClampingTechnique : public OverlayTechnique
    {
    public:
        //typedef osg::Group* (*TechniqueProvider)(class MapNode*);
        //static TechniqueProvider Provider;

    public:
        ClampingTechnique();

        /**
         * The size (resolution in both directions) of the depth map texture. By
         * default, this defaults to 4096 or your hardware's maximum supported
         * texture size, whichever is less.
         */
        void setTextureSize( int texSize );
        int getTextureSize() const { return *_textureSize; }


    public: // OverlayTechnique

        bool constrainOrthoZ() const override {
            return true;
        }

        bool hasData(
            OverlayDecorator::TechRTTParams& params) const;

        void reestablish(
            TerrainEngineNode* engine );

        void preCullTerrain(
            OverlayDecorator::TechRTTParams& params,
            osgUtil::CullVisitor*            cv );

        void cullOverlayGroup(
            OverlayDecorator::TechRTTParams& params,
            osgUtil::CullVisitor*            cv );

        void onInstall( TerrainEngineNode* engine );

        void onUninstall( TerrainEngineNode* engine );
        
        const osg::BoundingSphere& getBound(
            OverlayDecorator::TechRTTParams& params) const;

    protected:
        virtual ~ClampingTechnique() { }

    private:
        int                _textureUnit;
        optional<int>      _textureSize;
        TerrainEngineNode* _engine;

        mutable ClampingManager _clampingManager;
        ClampingManager& getClampingManager() { return _clampingManager; }
        friend class osgEarth::MapNode;

    private:
        void setUpCamera(OverlayDecorator::TechRTTParams& params);
    };

} }

#endif //OSGEARTH_OVERLAY_CLAMPING_TECHNIQUE