oglplus/019_gs_tessell.cpp

Shows how to do simple tessellation with the geometry shader

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;
    GeometryShader gs;
    FragmentShader fs;

    // Program
    Program prog;

    // Handles for uniforms in prog
    Uniform<GLint> tess_level;
    Uniform<Vec2f> viewport_dimensions;
    Uniform<Mat4f> projection_matrix, camera_matrix, model_matrix;

    // 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())
     , shape_indices(make_shape.Indices())
     , tess_level(prog)
     , viewport_dimensions(prog)
     , projection_matrix(prog)
     , camera_matrix(prog)
     , model_matrix(prog)
    {
        vs.Source(
            "#version 330\n"

            "in vec4 Position;"

            "void main(void)"
            "{"
            "   gl_Position = Position;"
            "}"
        );
        vs.Compile();

        gs.Source(
            "#version 330\n"
            "layout (triangles) in;"
            "layout (triangle_strip, max_vertices = 48) out;"

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

            "uniform mat4 ProjectionMatrix, CameraMatrix, ModelMatrix;"
            "uniform vec2 ViewportDimensions;"
            "uniform int TessLevel;"

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

            "void make_triangle(vec4 p0, vec4 p1, vec4 p2)"
            "{"
            "   vec3 n0 = (ModelMatrix*vec4(p0.xyz, 0)).xyz;"
            "   vec3 n1 = (ModelMatrix*vec4(p1.xyz, 0)).xyz;"
            "   vec3 n2 = (ModelMatrix*vec4(p2.xyz, 0)).xyz;"

            "   vec4 m0 = ModelMatrix*p0;"
            "   vec4 m1 = ModelMatrix*p1;"
            "   vec4 m2 = ModelMatrix*p2;"

            "   vec4 c0 = ProjectionMatrix*CameraMatrix*m0;"
            "   vec4 c1 = ProjectionMatrix*CameraMatrix*m1;"
            "   vec4 c2 = ProjectionMatrix*CameraMatrix*m2;"

            "   vec2 s0 = ViewportDimensions * c0.xy/c0.w;"
            "   vec2 s1 = ViewportDimensions * c1.xy/c1.w;"
            "   vec2 s2 = ViewportDimensions * c2.xy/c2.w;"

            "   vec2 v0 = s2 - s1;"
            "   vec2 v1 = s0 - s2;"
            "   vec2 v2 = s1 - s0;"

            "   float d0 = abs(v1.x*v2.y-v1.y*v2.x)/length(v0);"
            "   float d1 = abs(v2.x*v0.y-v2.y*v0.x)/length(v1);"
            "   float d2 = abs(v0.x*v1.y-v0.y*v1.x)/length(v2);"

            "   geomNormal = normalize(n0+n1+n2);"

            "   gl_Position = c0;"
            "   geomColor = normalize(abs(vec3(1, 1, 1) - n0));"
            "   geomLightDir = LightPosition - m0.xyz;"
            "   geomDist = vec3(d0, 0.0, 0.0);"
            "   EmitVertex();"

            "   gl_Position = c1;"
            "   geomColor = normalize(abs(vec3(1, 1, 1) - n1));"
            "   geomLightDir = LightPosition - m1.xyz;"
            "   geomDist = vec3(0.0, d1, 0.0);"
            "   EmitVertex();"

            "   gl_Position = c2;"
            "   geomColor = normalize(abs(vec3(1, 1, 1) - n2));"
            "   geomLightDir = LightPosition - m2.xyz;"
            "   geomDist = vec3(0.0, 0.0, d2);"
            "   EmitVertex();"

            "   EndPrimitive();"
            "}"

            "void do_tess_1(vec4 p_0, vec4 p_1, vec4 p_2, int l)"
            "{"
            "   if(l == 1) make_triangle(p_0, p_1, p_2);"
            "   else"
            "   {"
            "       vec4 p01 = vec4(normalize(p_0.xyz+p_1.xyz), 1.0);"
            "       vec4 p12 = vec4(normalize(p_1.xyz+p_2.xyz), 1.0);"
            "       vec4 p20 = vec4(normalize(p_2.xyz+p_0.xyz), 1.0);"
            "       make_triangle(p_0, p01, p20);"
            "       make_triangle(p01, p_1, p12);"
            "       make_triangle(p20, p12, p_2);"
            "       make_triangle(p01, p12, p20);"
            "   }"
            "}"

            "void do_tess_0(vec4 p_0, vec4 p_1, vec4 p_2, int l)"
            "{"
            "   if(l == 0) make_triangle(p_0, p_1, p_2);"
            "   else"
            "   {"
            "       vec4 p01 = vec4(normalize(p_0.xyz+p_1.xyz), 1.0);"
            "       vec4 p12 = vec4(normalize(p_1.xyz+p_2.xyz), 1.0);"
            "       vec4 p20 = vec4(normalize(p_2.xyz+p_0.xyz), 1.0);"
            "       do_tess_1(p_0, p01, p20, l);"
            "       do_tess_1(p01, p_1, p12, l);"
            "       do_tess_1(p20, p12, p_2, l);"
            "       do_tess_1(p01, p12, p20, l);"
            "   }"
            "}"

            "void main(void)"
            "{"
            "   do_tess_0("
            "       gl_in[0].gl_Position,"
            "       gl_in[1].gl_Position,"
            "       gl_in[2].gl_Position,"
            "       TessLevel"
            "   );"
            "}"
        );
        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 = 0.7;"
            "   float Diffuse = max(dot("
            "       normalize(geomNormal),"
            "       normalize(geomLightDir)"
            "   )+0.1, 0.0)*1.4;"

            "   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(gs);
        prog.AttachShader(fs);
        prog.Link();
        prog.Use();

        tess_level.BindTo("TessLevel");
        viewport_dimensions.BindTo("ViewportDimensions");
        projection_matrix.BindTo("ProjectionMatrix");
        camera_matrix.BindTo("CameraMatrix");
        model_matrix.BindTo("ModelMatrix");

        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(0.7f, 0.7f, 0.7f, 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, 50
            )
        );
    }

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

        const Vec3f offsets[4] = {
            Vec3f( 2, 0, 0),
            Vec3f(-2, 0, 0),
            Vec3f( 0, 0, 2),
            Vec3f( 0, 0,-2)
        };

        for(int i=0; i!=4; ++i)
        {
            auto model =
                ModelMatrixf::RotationX(Degrees(time * 11))*
                ModelMatrixf::Translation(offsets[i])*
                ModelMatrixf::RotationZ(Degrees(time * (37+3*i)));

            GLint level = GLint(17.0 / (Length((
                Inverse(model)*
                Vec4f(camera.Position(), 1)
            ).xyz())+0.1));

            model_matrix.Set(model);
            tess_level.Set(level);

            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