From 41fcc996080cdf5a49eceabc4e0224bee7c387fc Mon Sep 17 00:00:00 2001
From: shivshank <shivshank@users.noreply.github.com>
Date: Sat, 28 Jul 2018 15:25:59 -0400
Subject: [PATCH] Add basic game of life example

---
 examples/game_of_life.rs | 150 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 150 insertions(+)
 create mode 100644 examples/game_of_life.rs

diff --git a/examples/game_of_life.rs b/examples/game_of_life.rs
new file mode 100644
index 0000000..7a67fe9
--- /dev/null
+++ b/examples/game_of_life.rs
@@ -0,0 +1,150 @@
+extern crate mini_gl_fb;
+
+use mini_gl_fb::{Config, BufferFormat};
+
+use std::time::SystemTime;
+
+const WIDTH: usize = 200;
+const HEIGHT: usize = 200;
+
+fn main() {
+    let mut fb = mini_gl_fb::get_fancy(Config {
+        window_title: "PSA: Conway wants you to appreciate group theory instead",
+        window_size: (800.0, 800.0),
+        buffer_size: (WIDTH as _, HEIGHT as _),
+        .. Default::default()
+    });
+
+    fb.change_buffer_format::<u8>(BufferFormat::R);
+    fb.use_post_process_shader(POST_PROCESS);
+
+    let mut neighbors = vec![0; WIDTH * HEIGHT];
+    let mut cells = vec![false; WIDTH * HEIGHT];
+
+    cells[5 * WIDTH + 10] = true;
+    cells[5 * WIDTH + 11] = true;
+    cells[5 * WIDTH + 12] = true;
+
+    let mut previous = SystemTime::now();
+
+    while fb.is_running() {
+        let elapsed = previous.elapsed().unwrap();
+        let seconds = elapsed.as_secs() as f64 + elapsed.subsec_nanos() as f64 * 1e-9;
+
+        // Each generation should stay on screen for half a second
+        if seconds > 0.5 {
+            previous = SystemTime::now();
+            calculate_neighbors(&mut cells, &mut neighbors);
+            make_some_babies(&mut cells, &mut neighbors);
+            // Vsync should be enabled by default (open an issue if you need it disabled)
+            // Vsync should cause this to block so we don't run too often or too fast #robust
+            fb.update_buffer(&cells);
+        }
+    }
+}
+
+fn calculate_neighbors(cells: &mut [bool], neighbors: &mut [u32]) {
+    // a very basic GOL implementation; assumes outside the grid is dead
+    for y in 0..HEIGHT {
+        for x in 0..WIDTH {
+            let mut n = 0;
+
+            // Above
+            if y > 0 {
+                let j = y - 1;
+                if x > 0 && cells[j * WIDTH + x - 1] {
+                    n += 1;
+                }
+                if cells[j * WIDTH + x] {
+                    n += 1;
+                }
+                if x < (WIDTH - 1) && cells[j * WIDTH + x + 1] {
+                    n += 1;
+                }
+            }
+
+            // On the same line
+            if x > 0 && cells[y * WIDTH + x - 1] {
+                n += 1;
+            }
+            if x < (WIDTH - 1) && cells[y * WIDTH + x + 1] {
+                n += 1;
+            }
+
+            // Below
+            if y < (HEIGHT - 1) {
+                let j = y + 1;
+                if x > 0 && cells[j * WIDTH + x - 1] {
+                    n += 1;
+                }
+                if cells[j * WIDTH + x] {
+                    n += 1;
+                }
+                if x < (WIDTH - 1) && cells[j * WIDTH + x + 1] {
+                    n += 1;
+                }
+            }
+
+            let cell = y * WIDTH + x;
+            neighbors[cell] = n;
+        }
+    }
+}
+
+fn make_some_babies(cells: &mut [bool], neighbors: &mut [u32]) {
+    for y in 0..HEIGHT {
+        for x in 0..WIDTH {
+            let cell = y * WIDTH + x;
+
+            if !cells[cell] {
+                // if this cell is dead
+                if neighbors[cell] == 3 {
+                    // and it has three neighbors...
+                    cells[cell] = true;
+                }
+                // else it stays dead
+                continue;
+            }
+            // the cell is alive
+
+            if neighbors[cell] <= 1 {
+                // die from under population
+                cells[cell] = false;
+            } else if neighbors[cell] >= 3 {
+                // die from over population
+                cells[cell] = false;
+            }
+            // else: survive to the next generation
+        }
+    }
+}
+
+const POST_PROCESS: &str = "
+    bool on_grid_line(float pos) {
+        if (fract(pos) < 0.2) {
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    void main_image( out vec4 r_frag_color, in vec2 uv )
+    {
+        // A bool is stored as 1 in our image buffer
+        // OpenGL will map that u8/bool onto the range [0, 1]
+        // so the u8 1 in the buffer will become 1 / 255 or 0.0
+        // multiply by 255 to turn 1 / 255 into full intensity and leave 0 as 0
+
+        vec3 sample = texture(u_buffer, uv).rrr * 255.0;
+
+        // invert it since that's how GOL stuff is typically shown
+        sample = 1.0 - sample;
+
+        // attempt to add some grid lines (assumes width and height of image are 200)...
+        vec2 grid_pos = uv * 200;
+        if (on_grid_line(grid_pos.x) || on_grid_line(grid_pos.y)) {
+            sample = max(sample - 0.4, vec3(0.0, 0.0, 0.0));
+        }
+        r_frag_color = vec4(sample, 1.0);
+    }
+";