From 4dd892442742254e2bbf0f8b081548218460ca1b Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Thu, 18 Aug 2022 11:37:29 -0700
Subject: [PATCH] clean up ortho2d to do less things

---
 src/math.zig | 23 +++++++----------------
 1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/src/math.zig b/src/math.zig
index 81c1f15b1..a5d526578 100644
--- a/src/math.zig
+++ b/src/math.zig
@@ -3,22 +3,13 @@ pub const F32x4 = @Vector(4, f32);
 /// Matrix type
 pub const Mat = [4]F32x4;
 
-/// Identity matrix
-pub fn identity() Mat {
+pub fn ortho2d(left: f32, right: f32, bottom: f32, top: f32) Mat {
+    const w = right - left;
+    const h = top - bottom;
     return .{
-        .{ 1.0, 0.0, 0.0, 0.0 },
-        .{ 0.0, 1.0, 0.0, 0.0 },
-        .{ 0.0, 0.0, 1.0, 0.0 },
-        .{ 0.0, 0.0, 0.0, 1.0 },
+        .{ 2 / w, 0, 0, 0 },
+        .{ 0, 2 / h, 0, 0 },
+        .{ 0.0, 0.0, -1.0, 0.0 },
+        .{ -(right + left) / w, -(top + bottom) / h, 0.0, 1.0 },
     };
 }
-
-pub fn ortho2d(left: f32, right: f32, bottom: f32, top: f32) Mat {
-    var mat = identity();
-    mat[0][0] = 2 / (right - left);
-    mat[1][1] = 2 / (top - bottom);
-    mat[2][2] = -1.0;
-    mat[3][0] = -(right + left) / (right - left);
-    mat[3][1] = -(top + bottom) / (top - bottom);
-    return mat;
-}