From 0b7da3fad7b21bfacfd38c0cc59fc9a370c6acaf Mon Sep 17 00:00:00 2001
From: Abdelrahman <said.abdelrahman89@gmail.com>
Date: Sun, 15 Sep 2024 23:20:10 +0100
Subject: [PATCH] Cleanup, extra comments and error logging

---
 src/main.cc | 43 ++++++++++++++++++++++++++++++++++---------
 1 file changed, 34 insertions(+), 9 deletions(-)

diff --git a/src/main.cc b/src/main.cc
index 96f7ff2..2354d92 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -38,6 +38,7 @@ struct App {
   GLuint        vbo;
 
   GLuint        shader_program;
+  bool          running;
 };
 
 int    init                    (App &app);
@@ -55,8 +56,10 @@ int main() {
     return result;
   }
 
+  // Setup the geometry
   create_vertex_spec(app);
 
+  // Setup graphics pipeline. At the very minimum creating vertex and fragment shaders
   create_graphics_pipeline(app);
 
   run_main_loop(app);
@@ -92,7 +95,7 @@ int init(App &app) {
     return EXIT_CODE_OPENGL_CONTEXT_FAILED;
   }
 
-  // Init glad
+  // Init GLAD
   if (!gladLoadGLLoader(SDL_GL_GetProcAddress)) {
     fprintf(stderr, "Failed to initialise glad");
     return EXIT_CODE_GLAD_LOADER_FAILED;
@@ -110,11 +113,12 @@ int init(App &app) {
 
 void create_vertex_spec(App &app) {
   const std::vector<GLfloat> vertices = {
-    -0.8f, -0.8f, 0.0f,
-     0.8f, -0.8f, 0.0f,
-     0.0f,  0.8f, 0.0f,
+    -0.8f, -0.8f, 0.0f, // position
+     0.8f, -0.8f, 0.0f, // position
+     0.0f,  0.8f, 0.0f, // position
   };
 
+  // Create and activate the VAO
   glGenVertexArrays(1, &app.vao);
   glBindVertexArray(app.vao);
 
@@ -134,7 +138,8 @@ void create_vertex_spec(App &app) {
   // for each vertex and the offset of the first instance of the component in the buffer
   glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void *)0);
 
-  // Cleanup. The order matters. Unbind VAO first then disable the attributes. If you do it the
+  // Cleanup.
+  // The order matters. Unbind VAO first then disable the attributes. If you do it the
   // other way around, the VAO will store that the attributes are disabled and nothing will be
   // drawn during the rendering stage
   glBindVertexArray(0);
@@ -160,13 +165,13 @@ void create_graphics_pipeline(App &app) {
 }
 
 void run_main_loop(App &app) {
-  bool running = true;
+  app.running = true;
 
-  while (running) {
+  while (app.running) {
     while (SDL_PollEvent(&app.event)) {
       switch (app.event.type) {
       case SDL_QUIT:
-        running = false;
+        app.running = false;
         break;
       }
     }
@@ -188,6 +193,9 @@ void run_main_loop(App &app) {
     glDrawArrays(GL_TRIANGLES, 0, 3);
     // End draw call
 
+    // Not necessary if we only have one shader program
+    glUseProgram(0);
+
     SDL_GL_SwapWindow(app.window);
   }
 }
@@ -207,8 +215,25 @@ GLuint create_shader_program(const std::string &vertex_shader_source, const std:
   glAttachShader(shader_program, fragment_shader);
   glLinkProgram (shader_program);
 
+  GLint link_status;
+  glGetProgramiv(shader_program, GL_LINK_STATUS, &link_status);
+  if (link_status != GL_TRUE) {
+    GLsizei log_length = 0;
+    GLchar message[1024];
+    glGetProgramInfoLog(shader_program, 1024, &log_length, message);
+    fprintf(stderr, "Failed to link program: %s\n", message);
+  }
+
   // Validate the shader_program
   glValidateProgram(shader_program);
+  GLint validation_status;
+  glGetProgramiv(shader_program, GL_VALIDATE_STATUS, &validation_status);
+  if (validation_status != GL_TRUE) {
+    GLsizei log_length = 0;
+    GLchar message[1024];
+    glGetProgramInfoLog(shader_program, 1024, &log_length, message);
+    fprintf(stderr, "Failed to validate program: %s\n", message);
+  }
 
   return shader_program;
 }
@@ -226,7 +251,7 @@ GLuint compile_shader(GLuint type, const std::string &source) {
     GLsizei log_length = 0;
     GLchar message[1024];
     glGetShaderInfoLog(shader, 1024, &log_length, message);
-    fprintf(stderr, "%s\n", message);
+    fprintf(stderr, "Failed to compile shader: %s\n", message);
   }
 
   return shader;