From c98cce478e902e8569dd59dc1d5748ec85cc6a69 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Thu, 13 May 2021 21:01:57 -0400
Subject: math: matrix: Add in-place orthographic/perspective projection
 procedures.

---
 chickadee/math/matrix.scm | 34 ++++++++++++++++++++++++----------
 1 file changed, 24 insertions(+), 10 deletions(-)

diff --git a/chickadee/math/matrix.scm b/chickadee/math/matrix.scm
index f16e583..b79c94d 100644
--- a/chickadee/math/matrix.scm
+++ b/chickadee/math/matrix.scm
@@ -49,7 +49,9 @@
             matrix4-mult!
             matrix4*
             matrix4-identity!
+            orthographic-projection!
             orthographic-projection
+            perspective-projection!
             perspective-projection
             look-at!
             look-at
@@ -520,11 +522,9 @@ column-major format."
     (matrix4-identity! matrix)
     matrix))
 
-(define (orthographic-projection left right top bottom near far)
-  "Return a new matrix4 that represents an orthographic projection for
-the horizontal clipping plane LEFT and RIGHT, the vertical clipping
-plane TOP and BOTTOM, and the depth clipping plane NEAR and FAR."
-  (make-matrix4 (/ 2 (- right left)) 0.0 0.0 0.0
+(define (orthographic-projection! matrix left right top bottom near far)
+  (init-matrix4 matrix
+                (/ 2 (- right left)) 0.0 0.0 0.0
                 0.0 (/ 2 (- top bottom)) 0.0 0.0
                 0.0 0.0 (/ 2 (- far near)) 0.0
                 (- (/ (+ right left) (- right left)))
@@ -532,16 +532,30 @@ plane TOP and BOTTOM, and the depth clipping plane NEAR and FAR."
                 (- (/ (+ far near) (- far near)))
                 1.0))
 
-(define (perspective-projection field-of-vision aspect-ratio near far)
-  "Return a new matrix4 that represents a perspective projection with
-a FIELD-OF-VISION in radians, the desired ASPECT-RATIO, and the depth
-clipping plane NEAR and FAR."
+(define (orthographic-projection left right top bottom near far)
+  "Return a new matrix4 that represents an orthographic projection for
+the horizontal clipping plane LEFT and RIGHT, the vertical clipping
+plane TOP and BOTTOM, and the depth clipping plane NEAR and FAR."
+  (let ((matrix (make-null-matrix4)))
+    (orthographic-projection! matrix left right top bottom near far)
+    matrix))
+
+(define (perspective-projection! matrix field-of-vision aspect-ratio near far)
   (let ((f (cotan (/ field-of-vision 2))))
-    (make-matrix4 (/ f aspect-ratio) 0 0 0
+    (init-matrix4 matrix
+                  (/ f aspect-ratio) 0 0 0
                   0 f 0 0
                   0 0 (/ (+ far near) (- near far)) -1
                   0 0 (/ (* 2 far near) (- near far)) 0)))
 
+(define (perspective-projection field-of-vision aspect-ratio near far)
+  "Return a new matrix4 that represents a perspective projection with
+a FIELD-OF-VISION in radians, the desired ASPECT-RATIO, and the depth
+clipping plane NEAR and FAR."
+  (let ((matrix (make-null-matrix4)))
+    (perspective-projection! matrix field-of-vision aspect-ratio near far)
+    matrix))
+
 (define (look-at! matrix eye at up)
   ;; TODO: Eliminate allocation of vectors.
   (let* ((zaxis (vec3-normalize (vec3- at eye)))
-- 
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