From f56d1e558efe36a700a8fe67927a2f2e44f88eb8 Mon Sep 17 00:00:00 2001
From: Kienan Stewart <kienan.stewart@burntworld.ca>
Date: Wed, 19 Feb 2020 21:54:31 -0500
Subject: [PATCH] Add an MVP projection matrix with adjustable FoV

---
 README.md                            |  3 +++
 src/client/client_imgui.cpp          | 19 +++++++++++++++----
 src/shaders/defaultVertexShader.glsl |  2 ++
 3 files changed, 20 insertions(+), 4 deletions(-)
 create mode 100644 README.md

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..35a615c
--- /dev/null
+++ b/README.md
@@ -0,0 +1,3 @@
+# Prerequestes
+
+` sudo apt install libglm-dev`
diff --git a/src/client/client_imgui.cpp b/src/client/client_imgui.cpp
index cd66bee..2d6577c 100644
--- a/src/client/client_imgui.cpp
+++ b/src/client/client_imgui.cpp
@@ -9,7 +9,7 @@
 
 #include <glad/glad.h>
 #include <GLFW/glfw3.h>
-
+#include <glm/gtc/matrix_transform.hpp>
 #include "common/logging.hpp"
 #include "common/messaging/bus.hpp"
 
@@ -78,7 +78,7 @@ int main(int argc, char** argv)
 
     int height = 0, width = 0;
     ImVec4 clear_color = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);
-
+    float fov = 45.0;
     // Triangle example
     // @see http://www.opengl-tutorial.org/beginners-tutorials/tutorial-2-the-first-triangle/
     GLuint VertexArrayID;
@@ -109,6 +109,11 @@ int main(int argc, char** argv)
     static std::vector<RegisteredShaderProgram> shader_program_registry;
     loadShaderProgramsFromFile("shaders/shader_programs.txt", &shader_registry, &shader_program_registry);
     messager.registerCallback(&debug_messagebus_callback);
+    int window_height, window_width;
+    glm::mat4 projection;
+    glm::mat4 view = glm::lookAt(glm::vec3(4,3,3), glm::vec3(0,0,0), glm::vec3(0,1,0));
+    glm::mat4 model_default = glm::mat4(1.0f);
+    glm::mat4 mvp_matrix;
     while(!glfwWindowShouldClose(window)) {
        glfwPollEvents();
        // Process input.
@@ -127,10 +132,17 @@ int main(int argc, char** argv)
        glClear(GL_COLOR_BUFFER_BIT);
 
        // Render game geometries
+       glfwGetWindowSize(window, &window_width, &window_height);
+       // 45d FoV
+       projection = glm::perspective(glm::radians(fov), (float) window_width / (float) window_height,
+                                     0.1f, 100.0f);
+       mvp_matrix = projection * view * model_default;
        // @see https://blog.conan.io/2019/06/26/An-introduction-to-the-Dear-ImGui-library.html
        // 1st attribute buffer : vertices
        GLuint p = find_shader_program_by_name("default", &shader_program_registry);
        glUseProgram(p);
+       GLuint matrix_id = glGetUniformLocation(p, "MVP");
+       glUniformMatrix4fv(matrix_id, 1, GL_FALSE, &mvp_matrix[0][0]);
        glEnableVertexAttribArray(0);
        glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
        glVertexAttribPointer(
@@ -151,12 +163,11 @@ int main(int argc, char** argv)
        ImGui_ImplGlfw_NewFrame();
        ImGui::NewFrame();
        {
-          static float f = 0.0f;
           static int counter = 0;
 
           ImGui::Begin("Misc");                          // Create a window called "Hello, world!" and append into it.
 
-          ImGui::SliderFloat("float", &f, 0.0f, 1.0f);            // Edit 1 float using a slider from 0.0f to 1.0f
+          ImGui::SliderFloat("Field of View (FOV)", &fov, 45.0f, 180.0f);            // Edit 1 float using a slider from 0.0f to 1.0f
           ImGui::ColorEdit3("clear color", (float*)&clear_color); // Edit 3 floats representing a color
 
           ImGui::Text("Application average %.3f ms/frame (%.1f FPS)", 1000.0f / ImGui::GetIO().Framerate, ImGui::GetIO().Framerate);
diff --git a/src/shaders/defaultVertexShader.glsl b/src/shaders/defaultVertexShader.glsl
index 67b0e7b..91573de 100644
--- a/src/shaders/defaultVertexShader.glsl
+++ b/src/shaders/defaultVertexShader.glsl
@@ -1,6 +1,8 @@
 #version 300 es
 layout(location = 0) in vec3 vertexPosition_modelspace;
+uniform mat4 MVP;
 void main(){
   gl_Position.xyz = vertexPosition_modelspace;
   gl_Position.w = 1.0;
+  gl_Position = MVP * gl_Position;
 }