oglplus/022_xyz_planes.cpp

Shows how to use clipping for proper blending of overlapping objects

Copyright 2008-2014 Matus Chochlik. Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

#include <oglplus/gl.hpp>
#include <oglplus/all.hpp>
#include <oglplus/shapes/twisted_torus.hpp>
#include <oglplus/shapes/plane.hpp>

#include <sstream>

#include "example.hpp"

namespace oglplus {

class TorusExample : public Example
{
private:
    // helper object building torus vertex attributes
    shapes::TwistedTorus make_torus;
    // helper object encapsulating torus drawing instructions
    shapes::DrawingInstructions torus_instr;
    // indices pointing to torus primitive elements
    shapes::TwistedTorus::IndexArray torus_indices;

    // similar helpers for the X-,Y- and Z-plane
    std::vector<shapes::Plane> make_plane;
    shapes::DrawingInstructions plane_instr;
    shapes::Plane::IndexArray plane_indices;

    static std::vector<shapes::Plane> make_plane_builders(void)
    {
        std::vector<shapes::Plane> result;
        result.push_back(shapes::Plane(
            Vec3f( 0.0f,  2.0f,  0.0f),
            Vec3f( 0.0f,  0.0f,  2.0f)
        ));
        result.push_back(shapes::Plane(
            Vec3f( 2.0f,  0.0f,  0.0f),
            Vec3f( 0.0f,  0.0f, -2.0f)
        ));
        result.push_back(shapes::Plane(
            Vec3f( 2.0f,  0.0f,  0.0f),
            Vec3f( 0.0f,  2.0f,  0.0f)
        ));
        return result;
    }

    // wrapper around the current OpenGL context
    Context gl;

    Shader torus_vs, plane_vs;
    Shader torus_fs, plane_fs;

    Program torus_prog, plane_prog;

    // Uniform references
    std::vector<ProgramUniform<GLfloat>> torus_clip_signs;
    std::vector<ProgramUniform<GLfloat>> plane_clip_signs;

    Lazy<ProgramUniform<Vec3f>> plane_normal;
    Lazy<ProgramUniform<Mat4f>>
        plane_camera_matrix,
        torus_camera_matrix,
        torus_model_matrix;

    // A vertex array objects for the rendered torus and planes
    VertexArray torus;
    Array<VertexArray> plane;

    // VBOs for the torus's vertex attributes
    Buffer torus_positions, torus_texcoords;
    // VBOs for plane vertex positions
    Array<Buffer> plane_positions;
public:
    TorusExample(void)
     : make_torus()
     , torus_instr(make_torus.Instructions())
     , torus_indices(make_torus.Indices())
     , make_plane(make_plane_builders())
     , plane_instr(make_plane[0].Instructions())
     , plane_indices(make_plane[0].Indices())
     , torus_vs(ShaderType::Vertex, ObjectDesc("Torus vertex"))
     , plane_vs(ShaderType::Vertex, ObjectDesc("Plane vertex"))
     , torus_fs(ShaderType::Fragment, ObjectDesc("Torus fragment"))
     , plane_fs(ShaderType::Fragment, ObjectDesc("Plane fragment"))
     , torus_prog(ObjectDesc("Torus"))
     , plane_prog(ObjectDesc("Plane"))
     , plane_normal(plane_prog, "Normal")
     , plane_camera_matrix(plane_prog, "CameraMatrix")
     , torus_camera_matrix(torus_prog, "CameraMatrix")
     , torus_model_matrix(torus_prog, "ModelMatrix")
     , plane(make_plane.size())
     , plane_positions(make_plane.size())
    {
        std::stringstream config;
        config << "#define PlaneCount " << plane.size() << '\n';

        ShaderInclude config_glsl("/config.glsl", config.str());

        torus_vs.Source(
            "#version 330\n"
            "#extension GL_ARB_shading_language_include : enable\n"
            "#include <config.glsl>\n"

            "uniform mat4 ProjectionMatrix, ModelMatrix, CameraMatrix;"
            "uniform float ClipSign[PlaneCount];"
            "uniform vec4 ClipPlane[PlaneCount];"
            "in vec4 Position;"
            "in vec2 TexCoord;"
            "out vec2 vertTexCoord;"
            "void main(void)"
            "{"
            "   vertTexCoord = TexCoord;"
            "   gl_Position = "
            "       ModelMatrix *"
            "       Position;"
            "   for(int p=0; p!=PlaneCount; ++p)"
            "   {"
            "       gl_ClipDistance[p] = "
            "           ClipSign[p]* "
            "           dot(ClipPlane[p], gl_Position);"
            "   }"
            "   gl_Position = "
            "       ProjectionMatrix *"
            "       CameraMatrix *"
            "       gl_Position;"
            "}"
        );

        torus_fs.Source(
            "#version 330\n"
            "in vec2 vertTexCoord;"
            "out vec4 fragColor;"
            "void main(void)"
            "{"
            "   float i = ("
            "       int(vertTexCoord.x*36) % 2+"
            "       int(vertTexCoord.y*24) % 2"
            "   ) % 2;"
            "   fragColor = vec4(1-i/2, 1-i/2, 1-i/2, 1.0);"
            "}"
        );

        torus_prog.AttachShader(torus_vs);
        torus_prog.AttachShader(torus_fs);
        torus_prog.BuildInclude("/");
        torus_prog.Use();

        // bind the VAO for the torus
        torus.Bind();

        // bind the VBO for the torus vertices
        torus_positions.Bind(Buffer::Target::Array);
        {
            std::vector<GLfloat> data;
            GLuint n_per_vertex = make_torus.Positions(data);
            // upload the data
            Buffer::Data(Buffer::Target::Array, data);
            // setup the vertex attribs array for the vertices
            VertexArrayAttrib attr(torus_prog, "Position");
            attr.Setup<GLfloat>(n_per_vertex);
            attr.Enable();
        }

        // bind the VBO for the torus UV-coordinates
        torus_texcoords.Bind(Buffer::Target::Array);
        {
            std::vector<GLfloat> data;
            GLuint n_per_vertex = make_torus.TexCoordinates(data);
            // upload the data
            Buffer::Data(Buffer::Target::Array, data);
            // setup the vertex attribs array for the vertices
            VertexArrayAttrib attr(torus_prog, "TexCoord");
            attr.Setup<GLfloat>(n_per_vertex);
            attr.Enable();
        }

        plane_vs.Source(
            "#version 330\n"
            "#extension GL_ARB_shading_language_include : enable\n"
            "#include <config.glsl>\n"

            "uniform mat4 ProjectionMatrix, CameraMatrix;"
            "uniform float ClipSign[PlaneCount];"
            "uniform vec4 ClipPlane[PlaneCount];"
            "uniform vec3 Normal;"
            "in vec4 Position;"
            "out vec3 vertColor;"
            "void main(void)"
            "{"
            "   gl_Position = Position;"
            "   for(int p=0; p!=PlaneCount; ++p)"
            "   {"
            "       gl_ClipDistance[p] = "
            "           ClipSign[p]* "
            "           dot(ClipPlane[p], gl_Position);"
            "   }"
            "   gl_Position = "
            "       ProjectionMatrix *"
            "       CameraMatrix *"
            "       gl_Position;"
            "   vertColor = normalize("
            "       abs(Normal) + "
            "       0.4*Position.xyz"
            "   );"
            "}"
        ).CompileInclude("/");

        plane_fs.Source(
            "#version 330\n"
            "in vec3 vertColor;"
            "out vec4 fragColor;"
            "void main(void)"
            "{"
            "   fragColor = vec4(vertColor, 0.7);"
            "}"
        ).Compile();

        plane_prog.AttachShader(plane_vs);
        plane_prog.AttachShader(plane_fs);
        plane_prog.Link();
        plane_prog.Use();


        ProgramUniform<Vec4f> torus_clip_plane(torus_prog, "ClipPlane");
        ProgramUniform<Vec4f> plane_clip_plane(plane_prog, "ClipPlane");
        ProgramUniform<GLfloat> torus_clip_sign(torus_prog, "ClipSign");
        ProgramUniform<GLfloat> plane_clip_sign(plane_prog, "ClipSign");
        for(std::size_t p=0; p!=plane.size(); ++p)
        {
            plane[p].Bind();

            plane_positions[p].Bind(Buffer::Target::Array);
            {
                std::vector<GLfloat> data;
                GLuint n = make_plane[p].Positions(data);
                // upload the data
                Buffer::Data(Buffer::Target::Array, data);
                VertexArrayAttrib attr(plane_prog, "Position");
                attr.Setup<GLfloat>(n);
                attr.Enable();
            }
            {
                auto eq = make_plane[p].Equation();
                torus_clip_plane[p].Set(eq);
                plane_clip_plane[p].Set(eq);
            }
            {
                torus_clip_signs.push_back(torus_clip_sign[p]);
                plane_clip_signs.push_back(plane_clip_sign[p]);
            }
        }

        //
        gl.ClearColor(0.8f, 0.8f, 0.7f, 0.0f);
        gl.ClearDepth(1.0f);
        gl.FrontFace(make_torus.FaceWinding());
        gl.Enable(Capability::DepthTest);
        gl.BlendFunc(BlendFn::SrcAlpha, BlendFn::OneMinusSrcAlpha);
    }

    void Reshape(GLuint width, GLuint height)
    {
        gl.Viewport(width, height);
        auto proj = CamMatrixf::PerspectiveX(
            Degrees(60),
            double(width)/height,
            1, 30
        );
        ProgramUniform<Mat4f>(torus_prog, "ProjectionMatrix").Set(proj);
        ProgramUniform<Mat4f>(plane_prog, "ProjectionMatrix").Set(proj);
    }

    void RenderTorus(void)
    {
        torus_prog.Use();
        torus.Bind();
        torus_instr.Draw(torus_indices);
    }

    void RenderPlane(std::size_t p)
    {
        gl.Enable(Capability::Blend);
        plane_prog.Use();
        plane_normal.Set(make_plane[p].Normal());
        plane[p].Bind();
        plane_instr.Draw(plane_indices);
        gl.Disable(Capability::Blend);
    }

    void BSP(const Mat4f& camera, std::size_t p)
    {
        assert(p < std::size_t(plane.size()));
        // the normal vector of the plane
        Vec4f normal(make_plane[p].Normal(), 0.0);
        // check if we are seeing the front or the back face
        GLfloat sign = ((camera*normal).z() >= 0.0f)? 1.0f: -1.0f;
        bool at_leaf = p+1 == plane.size();

        +(Functionality::ClipDistance|p);
        torus_clip_signs[p].Set(-sign);
        plane_clip_signs[p].Set(-sign);
        if(at_leaf) RenderTorus();
        else BSP(camera, p+1);
        -(Functionality::ClipDistance|p);

        RenderPlane(p);

        +(Functionality::ClipDistance|p);
        torus_clip_signs[p].Set(+sign);
        plane_clip_signs[p].Set(+sign);
        if(at_leaf) RenderTorus();
        else BSP(camera, p+1);
        -(Functionality::ClipDistance|p);

    }

    void Render(double time)
    {
        gl.Clear().ColorBuffer().DepthBuffer();

        auto camera = CamMatrixf::Orbiting(
            Vec3f(),
            6.0,
            FullCircles(time / 10.0),
            Degrees(45.0 + SineWave(time / 7.0)*30.0)
        );
        auto model = ModelMatrixf::RotationX(FullCircles(time / 12.0));

        plane_camera_matrix.Set(camera);
        torus_camera_matrix.Set(camera);
        torus_model_matrix.Set(model);

        BSP(camera, 0);
    }

    bool Continue(double time)
    {
        return time < 30.0;
    }
};

void setupExample(ExampleParams& /*params*/){ }

std::unique_ptr<ExampleThread> makeExampleThread(
    Example& /*example*/,
    unsigned /*thread_id*/,
    const ExampleParams& /*params*/
){ return std::unique_ptr<ExampleThread>(); }

std::unique_ptr<Example> makeExample(const ExampleParams& /*params*/)
{
    return std::unique_ptr<Example>(new TorusExample);
}

} // namespace oglplus