oglplus/002_rect.cpp

Shows how to draw a shaded rectangle

Copyright 2008-2013 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"

#include <sstream>

namespace oglplus {

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

    // Vertex and fragment shader
    Shader vs, fs;

    // Program
    Program prog;

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

    // VBOs for the rectangle's vertices and colors
    Buffer verts;
    Buffer colors;
public:
    RectangleExample(void)
     : vs(ShaderType::Vertex)
     , fs(ShaderType::Fragment)
    {
        // this could be any istream
        std::stringstream vs_source(
            "#version 330\n"
            "in vec2 Position;"
            "in vec3 Color;"
            "out vec3 vertColor;"
            "void main(void)"
            "{"
            "   vertColor = Color;"
            "   gl_Position = vec4(Position, 0.0, 1.0);"
            "}"
        );
        // set the vertex shader source
        vs.Source(GLSLSource::FromStream(vs_source));
        // compile it
        vs.Compile();

        std::stringstream fs_source(
            "#version 330\n"
            "in vec3 vertColor;"
            "out vec4 fragColor;"
            "void main(void)"
            "{"
            "   fragColor = vec4(vertColor, 1.0);"
            "}"
        );
        // set the fragment shader source
        fs.Source(GLSLSource::FromStream(fs_source));
        // 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<Vec2f>().Enable();

        GLfloat rectangle_colors[12] = {
            1.0f, 1.0f, 1.0f,
            1.0f, 0.0f, 0.0f,
            0.0f, 1.0f, 0.0f,
            0.0f, 0.0f, 1.0f,
        };
        // bind the VBO for the rectangle colors
        colors.Bind(Buffer::Target::Array);
        // upload the data
        Buffer::Data(Buffer::Target::Array, 12, rectangle_colors);
        // setup the vertex attribs array for the vertices
        VertexArrayAttrib color_attr(prog, "Color");
        color_attr.Setup<Vec3f>().Enable();
        //
        gl.Disable(Capability::DepthTest);
    }

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

    void Render(double)
    {
        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