[dia] [transform] Implement dia_matrix_is_identity()

[Hans Breuer <hans src gnome org>]

commit c7bf9817b5a4aef6716ac9388d988cf5ddf54887
Author: Hans Breuer <hans breuer org>
Date:   Fri Oct 8 20:43:05 2010 +0200

    [transform] Implement dia_matrix_is_identity()

 lib/geometry.c |   15 +++++++++++++++
 lib/geometry.h |    2 ++
 2 files changed, 17 insertions(+), 0 deletions(-)
---
diff --git a/lib/geometry.c b/lib/geometry.c
index 290b63c..74567af 100644
--- a/lib/geometry.c
+++ b/lib/geometry.c
@@ -780,3 +780,18 @@ calculate_object_edge(Point *objmid, Point *end, DiaObject *obj)
   return mid2;
 }
 
+gboolean 
+dia_matrix_is_identity (const DiaMatrix *matrix)
+{
+  const real epsilon = 1e-6;
+  if (   fabs(matrix->xx - 1.0) < epsilon
+      && fabs(matrix->yy - 1.0) < epsilon
+      && fabs(matrix->xy) < epsilon
+      && fabs(matrix->yx) < epsilon
+      && fabs(matrix->x0) < epsilon
+      && fabs(matrix->y0) < epsilon)
+    return TRUE;
+
+  return FALSE;
+}
+
diff --git a/lib/geometry.h b/lib/geometry.h
index 6d7eb8f..1088af4 100644
--- a/lib/geometry.h
+++ b/lib/geometry.h
@@ -125,6 +125,8 @@ struct _DiaMatrix {
   real x0; real y0;
 };
 
+gboolean dia_matrix_is_identity (const DiaMatrix *matix);
+
 #define ROUND(x) ((int) floor((x)+0.5))
 
 /* inline these functions if the platform supports it */