oglplus/008_lyapunov.cpp

Shows how to draw the Lyapunov fractal

Author

Timo Keller

Matus Chochlik

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 "example.hpp"

namespace oglplus {

class RectangleExample : public Example
{
private:
    // wrapper around the current OpenGL context
    Context gl;

    // Program
    Program prog;

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

    // VBOs for the rectangle's vertices and the viewport coordinates
    Buffer verts;
    Buffer coords;

    // Scroll factor
    Lazy<Uniform<GLfloat>> scroll_factor;
public:
    RectangleExample(void)
     : scroll_factor(prog, "ScrollFactor")
    {
        // Vertex shader
        VertexShader vs;
        // Set the vertex shader source
        vs.Source(" \
            #version 330\n \
            uniform float ScrollFactor; \
            in vec2 Position; \
            in vec2 Coord; \
            out vec2 vertCoord; \
            void main(void) \
            { \
                vertCoord = ScrollFactor * Coord; \
                gl_Position = vec4(Position, 0.0, 1.0); \
            } \
        ");
        // compile it
        vs.Compile();

        // Fragment shader
        FragmentShader fs;
        // set the fragment shader source
        fs.Source(" \
            #version 330\n \
            in vec2 vertCoord; \
            out vec4 fragColor; \
            const int npasses = 100; \
            const int nclr = 5; \
            uniform vec4 clrs[5]; \
            void main(void) \
            { \
                vec2 ab = vertCoord; \
                float x_n = 0.5; \
                float sum = 0; \
                for (int i = 0; i < npasses; ++i) \
                { \
                    x_n = ab.x * x_n * (1 - x_n); \
                    sum += log(abs(ab.x*(1 - 2 * x_n))); \
                    x_n = ab.x * x_n * (1 - x_n); \
                    sum += log(abs(ab.x*(1 - 2 * x_n))); \
                    x_n = ab.x * x_n * (1 - x_n); \
                    sum += log(abs(ab.x*(1 - 2 * x_n))); \
                    x_n = ab.x * x_n * (1 - x_n); \
                    sum += log(abs(ab.x*(1 - 2 * x_n))); \
                    x_n = ab.x * x_n * (1 - x_n); \
                    sum += log(abs(ab.x*(1 - 2 * x_n))); \
                    x_n = ab.x * x_n * (1 - x_n); \
                    sum += log(abs(ab.x*(1 - 2 * x_n))); \
                    x_n = ab.y * x_n * (1.0 - x_n); \
                    sum += log(abs(ab.y*(1 - 2 * x_n))); \
                    x_n = ab.y * x_n * (1.0 - x_n); \
                    sum += log(abs(ab.y*(1 - 2 * x_n))); \
                    x_n = ab.y * x_n * (1.0 - x_n); \
                    sum += log(abs(ab.y*(1 - 2 * x_n))); \
                    x_n = ab.y * x_n * (1.0 - x_n); \
                    sum += log(abs(ab.y*(1 - 2 * x_n))); \
                    x_n = ab.y * x_n * (1.0 - x_n); \
                    sum += log(abs(ab.y*(1 - 2 * x_n))); \
                    x_n = ab.y * x_n * (1.0 - x_n); \
                    sum += log(abs(ab.y*(1 - 2 * x_n))); \
                } \
                float Lambda = sum / (12 * npasses); \
                float a = (clamp(Lambda, -2.0, 2.0) + 2.0) / 4; \
                for(int i = 0; i != (nclr - 1); ++i) \
                { \
                    if(a >= clrs[i].a && a < clrs[i+1].a) \
                    { \
                        float m = (a - clrs[i].a) / (clrs[i+1].a - clrs[i].a); \
                        fragColor = vec4( \
                            mix(clrs[i].rgb, clrs[i+1].rgb, m), \
                            1.0 \
                        ); \
                        break; \
                    } \
                } \
            } \
        ");
        // compile it
        fs.Compile();

        // attach the shaders to the program
        prog.AttachShader(vs);
        prog.AttachShader(fs);
        // link and use it
        prog.Link();
        prog.Use();

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

        GLfloat rectangle_verts[8] = {
            -1.0f, -1.0f,
            -1.0f,  1.0f,
             1.0f, -1.0f,
             1.0f,  1.0f
        };
        // bind the VBO for the rectangle vertices
        verts.Bind(Buffer::Target::Array);
        // upload the data
        Buffer::Data(Buffer::Target::Array, 8, rectangle_verts);
        // setup the vertex attribs array for the vertices
        VertexArrayAttrib vert_attr(prog, "Position");
        vert_attr.Setup<GLfloat>(2);
        vert_attr.Enable();

        GLfloat min = 3.0f;
        GLfloat max = 4.0f;
        GLfloat rectangle_coords[8] = {
             min, min,
             min, max,
             max, min,
             max, max
        };
        // bind the VBO for the rectangle vertices
        coords.Bind(Buffer::Target::Array);
        // upload the data
        Buffer::Data(Buffer::Target::Array, 8, rectangle_coords);
        // setup the vertex attribs array for the vertices
        VertexArrayAttrib coord_attr(prog, "Coord");
        coord_attr.Setup<GLfloat>(2);
        coord_attr.Enable();
        //
        // color map used in the fragment shader to colorize the fractal
        const GLuint nclr = 5;
        GLfloat colormap[nclr*4] = {
            0.4f, 0.2f, 1.0f, 0.00f,
            1.0f, 0.2f, 0.2f, 0.30f,
            1.0f, 1.0f, 1.0f, 0.95f,
            1.0f, 1.0f, 1.0f, 0.98f,
            0.1f, 0.1f, 0.1f, 1.00f
        };
        Uniform<Vec4f>(prog, "clrs").SetValues(nclr*4, colormap);
        //
        gl.Disable(Capability::DepthTest);
    }

    void Reshape(GLuint width, GLuint height)
    {
        gl.Viewport(width, height);
    }

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

        scroll_factor.Set(1.0f / (0.005 * time + 1.0f));

        gl.DrawArrays(PrimitiveType::TriangleStrip, 0, 4);
    }

    bool Continue(double time)
    {
        return time < 15.0;
    }
};

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 RectangleExample);
}

} // namespace oglplus