From 4dcc6025cbb4c3cd844ca568026ef7a653fa0a22 Mon Sep 17 00:00:00 2001
From: Pierre Joye <pierre.php@gmail.com>
Date: Thu, 26 Aug 2021 21:48:17 +0700
Subject: document gd Matrix

---
 src/gd_matrix.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

(limited to 'src')

diff --git a/src/gd_matrix.c b/src/gd_matrix.c
index ada63e6..def3f3c 100644
--- a/src/gd_matrix.c
+++ b/src/gd_matrix.c
@@ -12,7 +12,28 @@
 /**
  * Title: Matrix
  * Group: Affine Matrix
- */
+ *
+ * Matrix functions to initialize, transform and various other operations
+ * on these matrices.
+ * They can be used with gdTransformAffineCopy and are also used in various
+ * transformations functions in GD.
+ *
+ * matrix are create using a 6 elements double array:
+ * (start code)
+ * matrix[0] == xx
+ * matrix[1] == yx
+ * matrix[2] == xy
+ * matrix[3] == xy
+ * matrix[4] == x0
+ * matrix[5] == y0
+ * (end code)
+ * where the transformation of a given point (x,y) is given by:
+ *
+ * (start code)
+ * x_new = xx * x + xy * y + x0;
+ * y_new = yx * x + yy * y + y0;
+ * (end code)
+*/
 
 /**
  * Function: gdAffineApplyToPointF
-- 
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