Start code re-work Advanced OpenGL chapter.

src/4.advanced_opengl/9.1.geometry_shader_houses/9.1.geometry_shader.fs

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+#version 330 core
+in vec3 fColor;
+out vec4 color;
+
+void main()
+{
+    color = vec4(fColor, 1.0f);   
+}

src/4.advanced_opengl/9.1.geometry_shader_houses/9.1.geometry_shader.gs

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+#version 330 core
+layout (points) in;
+layout (triangle_strip, max_vertices = 5) out;
+
+in VS_OUT {
+    vec3 color;
+} gs_in[];
+
+out vec3 fColor;
+
+void build_house(vec4 position)
+{    
+    fColor = gs_in[0].color; // gs_in[0] since there's only one input vertex
+    gl_Position = position + vec4(-0.2f, -0.2f, 0.0f, 0.0f);    // 1:bottom-left   
+    EmitVertex();   
+    gl_Position = position + vec4( 0.2f, -0.2f, 0.0f, 0.0f);    // 2:bottom-right
+    EmitVertex();
+    gl_Position = position + vec4(-0.2f,  0.2f, 0.0f, 0.0f);    // 3:top-left
+    EmitVertex();
+    gl_Position = position + vec4( 0.2f,  0.2f, 0.0f, 0.0f);    // 4:top-right
+    EmitVertex();
+    gl_Position = position + vec4( 0.0f,  0.4f, 0.0f, 0.0f);    // 5:top
+    fColor = vec3(1.0f, 1.0f, 1.0f);
+    EmitVertex();
+    EndPrimitive();
+}
+
+void main() {    
+    build_house(gl_in[0].gl_Position);
+}

src/4.advanced_opengl/9.1.geometry_shader_houses/9.1.geometry_shader.vs

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+#version 330 core
+layout (location = 0) in vec2 position;
+layout (location = 1) in vec3 color;
+
+out VS_OUT {
+    vec3 color;
+} vs_out;
+
+void main()
+{
+    gl_Position = vec4(position.x, position.y, 0.0f, 1.0f); 
+    vs_out.color = color;
+}

src/4.advanced_opengl/9.1.geometry_shader_houses/geometry_shader_houses.cpp

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+// GLEW
+#define GLEW_STATIC
+#include <GL/glew.h>
+
+// GLFW
+#include <GLFW/glfw3.h>
+
+// GL includes
+#include <learnopengl/shader.h>
+
+// Properties
+GLuint screenWidth = 800, screenHeight = 600;
+
+bool keys[1024];
+void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode);
+
+// The MAIN function, from here we start our application and run our Game loop
+int main()
+{
+    // Init GLFW
+    glfwInit();
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
+    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
+    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
+
+    GLFWwindow* window = glfwCreateWindow(screenWidth, screenHeight, "LearnOpenGL", nullptr, nullptr); // Windowed
+    glfwMakeContextCurrent(window);
+
+    // Options
+    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);	
+
+    // Set the required callback functions
+    glfwSetKeyCallback(window, key_callback);
+
+    // Initialize GLEW to setup the OpenGL Function pointers
+    glewExperimental = GL_TRUE;
+    glewInit();
+
+    // Define the viewport dimensions
+    glViewport(0, 0, screenWidth, screenHeight);
+
+    // Setup and compile our shaders
+    Shader shader("geometry_shader.vs", "geometry_shader.frag", "geometry_shader.gs");
+
+    // Vertex data
+    GLfloat points[] = {
+        -0.5f,  0.5f, 1.0f, 0.0f, 0.0f, // Top-left
+         0.5f,  0.5f, 0.0f, 1.0f, 0.0f, // Top-right
+         0.5f, -0.5f, 0.0f, 0.0f, 1.0f, // Bottom-right
+        -0.5f, -0.5f, 1.0f, 1.0f, 0.0f  // Bottom-left
+    };
+    GLuint VBO, VAO;
+    glGenBuffers(1, &VBO);
+    glGenVertexArrays(1, &VAO);
+    glBindVertexArray(VAO);
+    glBindBuffer(GL_ARRAY_BUFFER, VBO);
+    glBufferData(GL_ARRAY_BUFFER, sizeof(points), &points, GL_STATIC_DRAW);
+    glEnableVertexAttribArray(0);
+    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), 0);
+    glEnableVertexAttribArray(1);
+    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (GLvoid*)(2 * sizeof(GLfloat)));
+    glBindVertexArray(0);
+
+    //glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
+
+    // Game loop
+    while(!glfwWindowShouldClose(window))
+    {
+        // Check and call events
+        glfwPollEvents();
+
+        // Clear buffers
+        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
+        glClear(GL_COLOR_BUFFER_BIT);
+
+        // Draw points
+        shader.Use();
+        glBindVertexArray(VAO);
+        glDrawArrays(GL_POINTS, 0, 4);
+        glBindVertexArray(0);
+        
+        // Swap the buffers
+        glfwSwapBuffers(window);
+    }
+
+    glfwTerminate();
+    return 0;
+}
+
+// Is called whenever a key is pressed/released via GLFW
+void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode)
+{
+    if(key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
+        glfwSetWindowShouldClose(window, GL_TRUE);
+
+    if(action == GLFW_PRESS)
+        keys[key] = true;
+    else if(action == GLFW_RELEASE)
+        keys[key] = false;	
+}