From bb353e8b085db0397d90be884924f79b879b2d9a Mon Sep 17 00:00:00 2001
From: Brendan Hansen <brendan.f.hansen@gmail.com>
Date: Tue, 20 Oct 2020 16:31:14 -0500
Subject: [PATCH] various changes

---
 include/utils.h | 22 ++++++++++++++++++++++
 src/sim.cpp     | 30 +++++++++++++++++++++++-------
 2 files changed, 45 insertions(+), 7 deletions(-)

diff --git a/include/utils.h b/include/utils.h
index 8c4ee7c..4b36e38 100644
--- a/include/utils.h
+++ b/include/utils.h
@@ -30,6 +30,28 @@ float randf();
 float randf(float max);
 float randf(float min, float max);
 
+
+/* "defer" is a useful construct from many other programming languages.
+It allows you to run a block of code at the end of a scope, but write the
+block of code in the middle of the the block. For example,
+
+void foo()
+{
+defer { printf("2\n"); };
+ printf("1\n");
+}
+
+This would print,
+
+1
+2
+
+This is very useful freeing mutex locks and closing files.
+
+The code below is the best way to do this in C++ using destructors.
+This code generates no overhead, in such a way that there is no extra
+function calls.
+ */
 #ifndef defer
 struct defer_dummy {};
 
diff --git a/src/sim.cpp b/src/sim.cpp
index 3af7c82..6a9e722 100644
--- a/src/sim.cpp
+++ b/src/sim.cpp
@@ -8,6 +8,7 @@
 #include <alloca.h>
 #include <unistd.h>
 #include <math.h>
+#include <time.h>
 
 #include <GLES3/gl3.h>
 #include <GLFW/glfw3.h>
@@ -198,10 +199,24 @@ update(f64 dt)
 {
 }
 
-internal GLsizei circle_mesh;
+internal GLuint body_buffer;
+internal Body*  body_data;
+
+internal GLuint circle_mesh;
 internal void
 draw()
 {
+    foreach(i, 0, 128)
+    {
+        body_data[i].pos = V2f{ randf(0, 800), randf(0, 800) };
+        body_data[i].vel = V2f{ 0.0f, 0.0f };
+        body_data[i].mass = randf(10.0f, 50.0f);
+    }
+    
+    glBindBuffer(GL_ARRAY_BUFFER, body_buffer);
+    glBufferSubData(GL_ARRAY_BUFFER, 0, 128 * sizeof(Body), body_data);
+    glBindBuffer(GL_ARRAY_BUFFER, -1);
+    
 	glClearColor(0.1, 0.1, 0.1, 1.0);
 	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
     
@@ -238,6 +253,8 @@ loop()
 i32
 main(i32 argc, char* argv[])
 {
+    srand(time(NULL));
+    
 	init_glfw();
     defer { deinit_glfw(); };
     
@@ -254,22 +271,21 @@ main(i32 argc, char* argv[])
     GLuint ortho_mat_loc = glGetUniformLocation(program, "u_proj");
     glUniformMatrix4fv(ortho_mat_loc, 1, false, (f32 *) ortho_mat);
     
-    auto bodies = alloc_bodies(128);
+    body_data = alloc_bodies(128);
     foreach(i, 0, 128)
     {
-        bodies[i].pos = V2f{ randf(0, 800), randf(0, 800) };
-        bodies[i].vel = V2f{ 0.0f, 0.0f };
-        bodies[i].mass = randf(10.0f, 50.0f);
+        body_data[i].pos = V2f{ randf(0, 800), randf(0, 800) };
+        body_data[i].vel = V2f{ 0.0f, 0.0f };
+        body_data[i].mass = randf(10.0f, 50.0f);
     }
     
     {
         glBindVertexArray(circle_mesh);
         defer { glBindVertexArray(-1); };
         
-        GLuint body_buffer;
         glGenBuffers(1, &body_buffer);
         glBindBuffer(GL_ARRAY_BUFFER, body_buffer);
-        glBufferData(GL_ARRAY_BUFFER, sizeof(Body) * 128, bodies, GL_STREAM_DRAW);
+        glBufferData(GL_ARRAY_BUFFER, sizeof(Body) * 128, body_data, GL_STREAM_DRAW);
         glEnableVertexAttribArray(1);
         glEnableVertexAttribArray(2);
         glVertexAttribDivisor(1, 1);
-- 
2.25.1