// This is public domain software and comes with
// absolutely no warranty. Use of public domain software
// may vary between counties, but in general you are free
// to use and distribute this software for any purpose.


// Example: OSG using an OpenGL 3.1 context.
// The comment block at the end of the source describes building OSG
// for use with OpenGL 3.x.

#include <osgViewer/Viewer>
#include <osgDB/ReadFile>
#include <osgDB/WriteFile>
#include <osg/GraphicsContext>
#include <osg/Camera>
#include <osg/Viewport>
#include <osg/StateSet>
#include <osg/Program>
#include <osg/Shader>
#include <osg/DrawMeshTasks>
#include <osg/DrawMeshTasksIndirect>
#include <osgUtil/Optimizer>

int main( int argc, char** argv )
{
    osg::ArgumentParser arguments( &argc, argv );

    static const char* meshSource = \
        "#version 450 \n"
        "#extension GL_NV_mesh_shader : enable\n"
        "layout(local_size_x = 3) in;"
        "layout(max_vertices = 64) out;"
        "layout(max_primitives = 126) out;"
        "layout(triangles) out;"
        "const vec3 vertices[3] = {vec3(-1,-1,0), vec3(1,-1,0), vec3(0,1,0)};"
        "void main()"
        "{"
            "uint id = gl_LocalInvocationID.x;"
            "gl_MeshVerticesNV[id].gl_Position = vec4(vertices[id], 2);"
            "gl_PrimitiveIndicesNV[id] = id;"
            "gl_PrimitiveCountNV = 1;"
        "}";


    static const char* fragmentSource = \
        "#version 450 \n"
        "#extension GL_NV_fragment_shader_barycentric : enable\n"
        "out vec4 color;"
        "void main()"
        "{"
            "color = vec4(gl_BaryCoordNV, 1.0);"
        "}";

    osg::ref_ptr<osg::Shader> vShader = new osg::Shader( osg::Shader::MESH, meshSource );
    osg::ref_ptr<osg::Shader> fShader = new osg::Shader( osg::Shader::FRAGMENT, fragmentSource );

    osg::ref_ptr<osg::Program> program = new osg::Program;
    program->addShader( vShader.get() );
    program->addShader( fShader.get() );

    osg::ref_ptr<osg::Group> group = new osg::Group;
    group->getOrCreateStateSet()->setAttribute( program.get() );

    group->addChild( new osg::DrawMeshTasks(0, 1) );

    // group->addChild( new osg::DrawMeshTasksIndirect(0) ); // will require a buffer to be bound.

    osgDB::writeNodeFile(*group, "test.osgt");

    osgViewer::Viewer viewer(arguments);

    viewer.setSceneData( group );

    // for non GL3/GL4 and non GLES2 platforms we need enable the osg_ uniforms that the shaders will use,
    // you don't need thse two lines on GL3/GL4 and GLES2 specific builds as these will be enable by default.
    //gc->getState()->setUseModelViewAndProjectionUniforms(true);
    //gc->getState()->setUseVertexAttributeAliasing(true);

    return( viewer.run() );
}