/* -*-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_SHADER_FACTORY_H
#define OSGEARTH_SHADER_FACTORY_H 1

#include <osgEarth/Common>
#include <osgEarth/VirtualProgram>
#include <osgEarth/ColorFilter>
#include <vector>

namespace osgEarth { namespace Util
{
    /**
     * A factory object that generates shader program "scaffolding" for VirtualProgram
     * attributes. Ths factory generates main() functions for each stage in the shader
     * pipline. You don't use it directly; instead you just create VirtualProgram
     * attributes, and those VPs will automatically invoke this factory object to
     * generate their main() functions.
     *
     * The default ShaderFactory is stored in the osgEarth registry. You can replace it,
     * but this is advanced usage and rarely necessary. If you think you need to alter
     * the built-in mains, consider whether you can accomplish your goal by using a
     * VirtualProgram instead!
     */
    class OSGEARTH_EXPORT ShaderFactory : public osg::Referenced
    {
    public:
        /**
         * Construtor
         */
        ShaderFactory();

        /**
         * Creates a Shader for each of the stages represented in the function map.
         */
        virtual VirtualProgram::StageMask createMains(
            osg::State& state,
            const VirtualProgram::FunctionLocationMap& unctions,
            const VirtualProgram::ShaderMap& in_shaders,
            const VirtualProgram::ExtensionsSet& in_extensions,
            std::vector< osg::ref_ptr<osg::Shader> >& out_mains) const;

        /**
         * Builds a shader function that executes an image filter chain.
         * @param functionName Name to give to the resulting shader function
         * @param chain        Color filter chain to execute
         */
        virtual osg::Shader* createColorFilterChainFragmentShader(
            const std::string&      functionName,
            const ColorFilterChain& chain ) const;

        /**
         * The name of the range uniform created by createRangeUniform().
         */
        virtual std::string getRangeUniformName() const;

        /**
         * Creates a uniform that's used by the RangeUniformCullCallback to convey
         * "distance to viewpoint" in a shader program.
         */
        osg::Uniform* createRangeUniform() const;

        //! Remove all preprocessor callbacks
        void clearProcessorCallbacks();

        //! Install a shader post-processing callback
        //! This will run on each shader before it gets included
        UID addPreProcessorCallback(
            osg::Referenced* host,
            std::function<void(std::string&, osg::Referenced*)>);

        //! Remove a callback you installed
        void removePreProcessorCallback(UID uid);

        //! Install a shader post-processing callback
        //! This will run on each shader before it gets included
        UID addPostProcessorCallback(
            osg::Referenced* host,
            std::function<void(osg::Shader*, osg::Referenced*)>);

        //! Remove a callback you installed
        void removePostProcessorCallback(UID uid);

        //! Returns a string you can use as your shader header,
        //! including the #version, precision, and extensions strings.
        static std::string getGLSLHeader();

    protected:
        /** dtor */
        virtual ~ShaderFactory() { }
    };

} } // namespace osgEarth

#endif // OSGEARTH_SHADER_FACTORY_H