gl

    // glsl 140 => opengl 3.1
    // https://stackoverflow.com/questions/19021567/
    std::string vertex_shader_scr =
        OD_GLSL(140,
            in  vec2 pos;
            in  vec2 vertex_uv;
            out vec2 uv;
            uniform  mat3 transform; // model view projection

            void main()
            {
                gl_Position = vec4(transform * vec3(pos, 1.0), 1.0);
                uv = vertex_uv;
            });

    std::string fragment_shader_scr =
        OD_GLSL(140,
            uniform sampler2D tex;
            uniform vec4 col;
            in  vec2 uv;
            out vec4 flagcolor;
            void main()
            {
                vec4 color = texture(tex, uv);
                flagcolor = color;
            });

    enum {
        position_attrib_index,
        texcoord_attrib_index,
    };
    const std::map<unsigned, std::string> attrib_map = {
        { position_attrib_index, "pos" },
        { texcoord_attrib_index, "vertex_uv" }
    };

    gl::Program program;
    {
        gl::Shader vertex_shader(gl::Shader::Vertex, vertex_shader_scr);
        gl::Shader fragment_shader(gl::Shader::Fragment, fragment_shader_scr);

        program.attach(vertex_shader);
        program.attach(fragment_shader);
        for(const auto& p: attrib_map)
            program.bindAttribLocation(p.first, p.second);
        program.link();


        program.detach(vertex_shader);
        program.detach(fragment_shader);
    }

    gl::Vao vao;
    gl::Vbo vbo_shape;

    {
        /*
        std::vector<float> data_pos = {
            // Vertex position
            0, 0,
            16, 0,
            16, 16,
            0, 16,

            // Vertex uv
            0, 0,
            1, 0,
            1, 1,
            0, 1
        };
        */
        std::vector<float> data_pos = {
            0, 0, 0, 0,
            16, 0, 1, 0,
            16, 16, 1, 1,
            0, 16, 0, 1
        };

        vbo_shape.bind();
        vbo_shape.data(data_pos.size() * sizeof(float), &data_pos[0]);

        vao.bind();
        vao.setVertexAttribf(vbo_shape, position_attrib_index, 2, false, 4 * sizeof(float), 0);
        vao.setVertexAttribf(vbo_shape, texcoord_attrib_index, 2, true, 4 * sizeof(float), 2);
        //vao.setVertexAttribf(vbo_shape, position_attrib_index, 2, false, 2 * sizeof(float), 0);
        //vao.setVertexAttribf(vbo_shape, texcoord_attrib_index, 2, false, 2 * sizeof(float), 8);
        vao.unbind();
    }

    program.use();
    unsigned uniform_color = gl::getUniformLocation(program.handle(), "col");
    unsigned uniform_transform = gl::getUniformLocation(program.handle(), "transform");
    GLfloat color[4] = {0.2f, 0.7f, 0.7f, 1.f};
    gl::uniform4fv(uniform_color, 1, static_cast<const GLfloat*>(color));
    program.unuse();

    od::View view(0, 0, win.width(), win.height());

    while(win.open())
    {
        win.ioHandle();

        if(od::keyPressed(od::vk_escape))
            break;

        if(od::keyCheck(od::vk_left)) { view.translate(1, 0); }
        if(od::keyCheck(od::vk_right)) { view.translate(-1, 0); }
        if(od::keyCheck(od::vk_up)) { view.translate(0, 1); }
        if(od::keyCheck(od::vk_down)) { view.translate(0, -1); }

        od::drawClear();
        win.updateView(view);

        {
            program.use();
            tex.texture().bind();

            od::Mat3 camera_matrix =
                    od::Mat3::ortho(
                        view.x(), view.x() + win.width(),
                        view.y() + win.height(), view.y());

            GLfloat color1[4] = {1.f, 1.f, 1.f, 1.f};
            gl::uniform4fv(uniform_color, 1, color1);

            for(int i=0; i<4; ++i)
            for(int j=0; j<4; ++j)
            {
                od::Mat3 model(1.f, 0.f, i*32.f,
                               0.f, 1.f, j*32.f,
                               0.f, 0.f, 1.f);

                gl::uniformMatrix(uniform_transform, camera_matrix * model);

                vao.bind();
                glDrawArrays(GL_QUADS, 0, 8);
                vao.unbind();
            }

            tex.texture().unbind();
            program.unuse();
        }

        tex.draw(tex.spriteIndex("tile"), 0, 16, 16);

        win.screenRefresh();
        od::framerateUpdate();
    }