Enable GL_BLEND

main.c

@@ -245,6 +245,9 @@ int main()
     glEnable(GL_DEBUG_OUTPUT);
     glDebugMessageCallback(MessageCallback, 0);
 
+    glEnable(GL_BLEND);
+    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+
     reload_shaders();
 
     glfwSetKeyCallback(window, key_callback);