oglplus/019_tessellation.cpp

Shows simple polyhedron tessellation

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/icosahedron.hpp>

#include "example.hpp"

namespace oglplus {

class TessellationExample : public Example
{
private:
    // helper object building shape vertex attributes
    shapes::SimpleIcosahedron make_shape;
    // helper object encapsulating shape drawing instructions
    shapes::DrawingInstructions shape_instr;
    // indices pointing to shape primitive elements
    shapes::SimpleIcosahedron::IndexArray shape_indices;

    // wrapper around the current OpenGL context
    Context gl;

    // Shaders
    VertexShader vs;
    TessControlShader cs;
    TessEvaluationShader es;
    GeometryShader gs;
    FragmentShader fs;

    // Program
    Program prog;

    // Uniforms
    Lazy<Uniform<Mat4f>> projection_matrix, camera_matrix, model_matrix;
    Lazy<Uniform<Vec3f>> offset, view_position;
    Lazy<Uniform<Vec2f>> viewport_dimensions;

    // A vertex array object for the rendered shape
    VertexArray shape;

    // VBOs for the shape's vertices and element indices
    Buffer verts, indices;
public:
    TessellationExample(void)
     : shape_instr(make_shape.Instructions(PrimitiveType::Patches))
     , shape_indices(make_shape.Indices())
     , vs(ObjectDesc("Vertex"))
     , cs(ObjectDesc("Tessellation Control"))
     , es(ObjectDesc("Tessellation Evaluation"))
     , gs(ObjectDesc("Geometry"))
     , fs(ObjectDesc("Fragment"))
     , projection_matrix(prog, "ProjectionMatrix")
     , camera_matrix(prog, "CameraMatrix")
     , model_matrix(prog, "ModelMatrix")
     , offset(prog, "Offset")
     , view_position(prog, "ViewPosition")
     , viewport_dimensions(prog, "ViewportDimensions")
    {
        vs.Source(
            "#version 330\n"

            "uniform vec3 ViewPosition;"

            "in vec3 Position;"

            "out vec3 vertPosition;"
            "out float vertDistance;"

            "void main(void)"
            "{"
            "   vertPosition = Position;"
            "   vertDistance = length(ViewPosition - vertPosition);"
            "}"
        );
        vs.Compile();

        cs.Source(
            "#version 330\n"
            "#extension ARB_tessellation_shader : enable\n"

            "layout(vertices = 3) out;"

            "in vec3 vertPosition[];"
            "in float vertDistance[];"

            "out vec3 tecoPosition[];"

            "int tessLevel(float dist)"
            "{"
            "   return int(9.0 / sqrt(dist+0.1));"
            "}"

            "void main(void)"
            "{"
            "   tecoPosition[gl_InvocationID] ="
            "       vertPosition[gl_InvocationID];"

            "   if(gl_InvocationID == 0)"
            "   {"
            "       gl_TessLevelInner[0] = tessLevel(("
            "           vertDistance[0]+"
            "           vertDistance[1]+"
            "           vertDistance[2] "
            "       )*0.333);"
            "       gl_TessLevelOuter[0] = tessLevel(("
            "           vertDistance[1]+"
            "           vertDistance[2] "
            "       )*0.5);"
            "       gl_TessLevelOuter[1] = tessLevel(("
            "           vertDistance[2]+"
            "           vertDistance[0] "
            "       )*0.5);"
            "       gl_TessLevelOuter[2] = tessLevel(("
            "           vertDistance[0]+"
            "           vertDistance[1] "
            "       )*0.5);"
            "   }"
            "}"
        );
        cs.Compile();

        es.Source(
            "#version 330\n"
            "#extension ARB_tessellation_shader : enable\n"

            "layout(triangles, equal_spacing, ccw) in;"

            "const vec3 LightPosition = vec3(12.0, 10.0, 7.0);"

            "uniform mat4 ProjectionMatrix, CameraMatrix, ModelMatrix;"

            "in vec3 tecoPosition[];"

            "out vec3 teevNormal;"
            "out vec3 teevLightDir;"

            "void main(void)"
            "{"
            "   vec3 p0 = gl_TessCoord.x * tecoPosition[0];"
            "   vec3 p1 = gl_TessCoord.y * tecoPosition[1];"
            "   vec3 p2 = gl_TessCoord.z * tecoPosition[2];"

            "   vec4 tempPosition = vec4(normalize(p0+p1+p2), 0.0);"
            "   teevNormal = (ModelMatrix * tempPosition).xyz;"
            "   tempPosition.w = 1.0;"
            "   tempPosition = ModelMatrix * tempPosition;"
            "   teevLightDir = LightPosition - tempPosition.xyz;"
            "   gl_Position = "
            "       ProjectionMatrix *"
            "       CameraMatrix *"
            "       tempPosition;"
            "}"
        );
        es.Compile();

        gs.Source(
            "#version 330\n"
            "layout (triangles) in;"
            "layout (triangle_strip, max_vertices = 3) out;"

            "uniform vec3 Offset;"
            "uniform vec2 ViewportDimensions;"

            "in vec3 teevNormal[], teevLightDir[];"

            "noperspective out vec3 geomDist;"
            "flat out vec3 geomNormal;"
            "out vec3 geomColor;"
            "out vec3 geomLightDir;"

            "void main(void)"
            "{"
            "   geomNormal = normalize("
            "       teevNormal[0]+"
            "       teevNormal[1]+"
            "       teevNormal[2]"
            "   );"

            "   vec2 ScreenPos[3];"
            "   for(int i=0; i!=3; ++i)"
            "   {"
            "       ScreenPos[i] = "
            "           ViewportDimensions*"
            "           gl_in[i].gl_Position.xy/"
            "           gl_in[i].gl_Position.w;"
            "   }"

            "   vec2 TmpVect[3];"
            "   for(int i=0; i!=3; ++i)"
            "   {"
            "       TmpVect[i] = "
            "           ScreenPos[(i+2)%3]-"
            "           ScreenPos[(i+1)%3];"
            "   }"

            "   const vec3 EdgeMask[3] = vec3[3]("
            "       vec3(1.0, 0.0, 0.0),"
            "       vec3(0.0, 1.0, 0.0),"
            "       vec3(0.0, 0.0, 1.0) "
            "   );"

            "   for(int i=0; i!=3; ++i)"
            "   {"
            "       float Dist = abs("
            "           TmpVect[(i+1)%3].x*TmpVect[(i+2)%3].y-"
            "           TmpVect[(i+1)%3].y*TmpVect[(i+2)%3].x "
            "       ) / length(TmpVect[i]);"
            "       vec3 DistVect = vec3(Dist, Dist, Dist);"

            "       gl_Position = gl_in[i].gl_Position;"
            "       geomColor = normalize(abs("
            "           vec3(2.0, 2.0, 2.0)-"
            "           teevNormal[i]-"
            "           Offset"
            "       ));"
            "       geomLightDir = teevLightDir[i];"
            "       geomDist = EdgeMask[i] * DistVect;"
            "       EmitVertex();"
            "   }"
            "   EndPrimitive();"
            "}"
        );
        gs.Compile();

        fs.Source(
            "#version 330\n"

            "noperspective in vec3 geomDist;"
            "flat in vec3 geomNormal;"
            "in vec3 geomColor;"
            "in vec3 geomLightDir;"

            "out vec3 fragColor;"

            "void main(void)"
            "{"
            "   float MinDist = min(min(geomDist.x,geomDist.y),geomDist.z);"
            "   float EdgeAlpha = exp2(-pow(MinDist, 2.0));"

            "   const float Ambient = 0.8;"
            "   float Diffuse = max(dot("
            "       normalize(geomNormal),"
            "       normalize(geomLightDir)"
            "   ), 0.0);"

            "   vec3 FaceColor = geomColor * (Diffuse + Ambient);"
            "   const vec3 EdgeColor = vec3(0.0, 0.0, 0.0);"

            "   fragColor = mix(FaceColor, EdgeColor, EdgeAlpha);"
            "}"
        );
        fs.Compile();

        prog.AttachShader(vs);
        prog.AttachShader(cs);
        prog.AttachShader(es);
        prog.AttachShader(gs);
        prog.AttachShader(fs);
        prog.Link();
        prog.Use();

        shape.Bind();

        verts.Bind(Buffer::Target::Array);
        {
            std::vector<GLfloat> data;
            GLuint n_per_vertex = make_shape.Positions(data);
            Buffer::Data(Buffer::Target::Array, data);
            VertexArrayAttrib attr(prog, "Position");
            attr.Setup<GLfloat>(n_per_vertex);
            attr.Enable();

            indices.Bind(Buffer::Target::ElementArray);
            Buffer::Data(Buffer::Target::ElementArray, shape_indices);
            shape_indices.clear();
        }

        //
        gl.ClearColor(0.8f, 0.8f, 0.8f, 0.0f);
        gl.ClearDepth(1.0f);
        gl.Enable(Capability::DepthTest);

        prog.Use();
    }

    void Reshape(GLuint width, GLuint height)
    {
        gl.Viewport(width, height);
        viewport_dimensions.Set(Vec2f(width, height));
        projection_matrix.Set(
            CamMatrixf::PerspectiveX(
                Degrees(60),
                double(width)/height,
                1, 40
            )
        );
    }

    void Render(double time)
    {
        gl.Clear().ColorBuffer().DepthBuffer();
        //
        auto camera = CamMatrixf::Orbiting(
            Vec3f(),
            14.0 - SineWave(time / 13)*8.0,
            Degrees(time * 33),
            Degrees(SineWave(time / 21.0) * 31)
        );
        camera_matrix.Set(camera);

        const Vec3f offsets[6] = {
            Vec3f( 2, 0, 0),
            Vec3f(-2, 0, 0),
            Vec3f( 0, 2, 0),
            Vec3f( 0,-2, 0),
            Vec3f( 0, 0, 2),
            Vec3f( 0, 0,-2)
        };

        for(int i=0; i!=6; ++i)
        {
            auto model =
                ModelMatrixf::RotationX(Degrees(time * 11))*
                ModelMatrixf::Translation(offsets[i])*
                ModelMatrixf::RotationZ(Degrees(time * (37+9*i)));

            model_matrix.Set(model);
            offset.Set(offsets[i]);
            view_position.Set((
                Inverse(model)*
                Vec4f(camera.Position(), 1)
            ).xyz());

            shape_instr.Draw(shape_indices);
        }
    }

    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 TessellationExample);
}

} // namespace oglplus