From a9a397ba97e7b9ce67256ed3d12958498a5a83d4 Mon Sep 17 00:00:00 2001
From: Levi Pearson <levi.pearson@harman.com>
Date: Sat, 30 Jul 2016 16:18:34 -0600
Subject: [PATCH] Refactor grid drawing for greater clarity

---
 src/game/map.rs | 45 ++++++++++++++++++++++-----------------------
 src/game/mod.rs |  4 ++--
 2 files changed, 24 insertions(+), 25 deletions(-)

diff --git a/src/game/map.rs b/src/game/map.rs
index 2a1846d..8ac967f 100644
--- a/src/game/map.rs
+++ b/src/game/map.rs
@@ -2,6 +2,7 @@ use piston_window::*;
 use piston_window::math::*;
 
 const GREEN: [f32; 4] = [0.0, 1.0, 0.0, 0.05];
+const GRID_SIZE: Scalar = 100.0;
 
 pub struct Map {
     pub width: Scalar,
@@ -19,43 +20,41 @@ impl Map {
 
     pub fn draw_grid<G>(&self,
                         cam_pos: Vec2d,
-                        cam_width: Scalar,
-                        cam_height: Scalar,
+                        cam_size: Vec2d,
                         draw_state: &DrawState,
                         transform: Matrix2d,
                         g: &mut G)
         where G: Graphics
     {
+        /* Camera coordinates will be centered in the screen, so find the
+           upper left and lower right coordinates */
+        let min = sub(cam_pos, mul_scalar(cam_size, 0.5));
+        let max = add(cam_pos, mul_scalar(cam_size, 0.5));
 
-        let xcount = (cam_width / 100.0).ceil() as u32 + 2;
-        let ycount = (cam_height / 100.0).ceil() as u32 + 2;
+        /* Determine the number of grid lines to draw in each direction */
+        let xcount = (cam_size[0] / GRID_SIZE).ceil() as u32 + 1;
+        let ycount = (cam_size[1] / GRID_SIZE).ceil() as u32 + 1;
 
-        let min_x = cam_pos[0] - cam_width / 2.0;
-        let min_y = cam_pos[1] - cam_height / 2.0;
+        /* Clamp the line coordinates to multiples of the grid size */
+        let first_x = (min[0] / GRID_SIZE).trunc() * GRID_SIZE;
+        let first_y = (min[1] / GRID_SIZE).trunc() * GRID_SIZE;
 
-        let first_x = (min_x / 100.0).trunc() * 100.0;
-        let first_y = (min_y / 100.0).trunc() * 100.0;
-
-        let start_y = cam_pos[1] - cam_height;
-        let end_y = cam_pos[1] + cam_height;
+        /* Draw vertical grid lines */
         for x in 0..xcount {
-            let line_x = first_x + (100.0 * x as Scalar);
-            let p1 = sub([line_x, start_y], cam_pos);
-            let p2 = sub([line_x, end_y], cam_pos);
+            let line_x = first_x + (GRID_SIZE * x as Scalar);
+            let p1 = [line_x, min[1]];
+            let p2 = [line_x, max[1]];
             Line::new(GREEN, 1.0)
-                .draw([p1[0], p1[1], p2[0], p2[1]],
-                      draw_state, transform, g);
+                .draw([p1[0], p1[1], p2[0], p2[1]], draw_state, transform, g);
         }
 
-        let start_x = cam_pos[0] - cam_width;
-        let end_x = cam_pos[0] + cam_width;
+        /* Draw horizontal grid lines */
         for y in 0..ycount {
-            let line_y = first_y + (100.0 * y as Scalar);
-            let p1 = sub([start_x, line_y], cam_pos);
-            let p2 = sub([end_x, line_y], cam_pos);
+            let line_y = first_y + (GRID_SIZE * y as Scalar);
+            let p1 = [min[0], line_y];
+            let p2 = [max[0], line_y];
             Line::new(GREEN, 1.0)
-                .draw([p1[0], p1[1], p2[0], p2[1]],
-                      draw_state, transform, g);
+                .draw([p1[0], p1[1], p2[0], p2[1]], draw_state, transform, g);
         }
     }
 }
diff --git a/src/game/mod.rs b/src/game/mod.rs
index 7eb8ca2..d64f3f3 100644
--- a/src/game/mod.rs
+++ b/src/game/mod.rs
@@ -74,10 +74,10 @@ impl Game {
             let cam_width = self.camera.width;
             let cam_height = self.camera.height;
 
-            self.map.draw_grid(cam_pos, cam_width, cam_height, &ds, ct, gl);
-
             let cam_trans = ct.append_transform(translate(mul_scalar(cam_pos, -1.0)));
 
+            self.map.draw_grid(cam_pos, [cam_width, cam_height], &ds, cam_trans, gl);
+
             for bullet in self.bullets.iter() {
                 draw_bullet(&bullet, &ds, cam_trans, gl);
             }