oglplus/004_rect.cpp

Shows how to draw a custom shaded rectangle

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;

    // Vertex and fragment shaders
    Shader vs, fs;

    // Program
    Program prog;

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

    // VBO for the rectangle's vertices
    Buffer verts;
public:
    RectangleExample(void)
     : vs(ShaderType::Vertex)
     , fs(ShaderType::Fragment)
    {
        // Set the vertex shader source
        vs.Source(" \
            #version 330\n \
            in vec2 Position; \
            out vec2 vertCoord; \
            void main(void) \
            { \
                vertCoord = Position; \
                gl_Position = vec4(Position, 0.0, 1.0); \
            } \
        ");
        // compile it
        vs.Compile();

        // set the fragment shader source
        fs.Source(" \
            #version 330\n \
            const float radius = 0.4; \
            in vec2 vertCoord; \
            uniform vec2 RedCenter, GreenCenter, BlueCenter; \
            out vec4 fragColor; \
            void main(void) \
            { \
                vec3 dist = vec3( \
                    distance(vertCoord, RedCenter), \
                    distance(vertCoord, GreenCenter), \
                    distance(vertCoord, BlueCenter) \
                ); \
                fragColor = vec4( \
                    dist.r < radius ? 1.0 : (2*radius - dist.r) / radius, \
                    dist.g < radius ? 1.0 : (2*radius - dist.g) / radius, \
                    dist.b < radius ? 1.0 : (2*radius - dist.b) / radius, \
                    1.0 \
                ); \
            } \
        ");
        // 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();
        //
        // Variables referencing the program's uniforms
        Uniform<Vec2f>(prog,   "RedCenter").Set(Vec2f(-0.141f, 0.141f));
        Uniform<Vec2f>(prog, "GreenCenter").Set(Vec2f(0.141f, 0.141f));
        Uniform<Vec2f>(prog,  "BlueCenter").Set(Vec2f(0.0f, -0.2f));

        gl.Disable(Capability::DepthTest);
    }

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

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

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

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