matrix: Adds cogl_matrix_is_identity API

This adds a function called cogl_matrix_is_identity that can determine
if a given matrix is an identity matrix or not.

Signed-off-by: Neil Roberts <neil@linux.intel.com>

cogl/cogl-matrix.c

@@ -2041,3 +2041,13 @@ cogl_matrix_project_points (const CoglMatrix *matrix,
                                       n_points);
     }
 }
+
+gboolean
+cogl_matrix_is_identity (const CoglMatrix *matrix)
+{
+  if (!(matrix->flags & MAT_DIRTY_TYPE) &&
+      matrix->type == COGL_MATRIX_TYPE_IDENTITY)
+    return TRUE;
+  else
+    return memcmp (matrix, identity, sizeof (float) * 16) == 0;
+}

cogl/cogl-matrix.h

@@ -585,6 +585,18 @@ cogl_matrix_project_points (const CoglMatrix *matrix,
 
 #endif /* COGL_ENABLE_EXPERIMENTAL_API */
 
+/**
+ * cogl_matrix_is_identity:
+ * @matrix: A #CoglMatrix
+ *
+ * Determines if the given matrix is an identity matrix.
+ *
+ * Returns: %TRUE if @matrix is an identity matrix else %FALSE
+ * Since: 1.8
+ */
+gboolean
+cogl_matrix_is_identity (const CoglMatrix *matrix);
+
 #ifdef _COGL_SUPPORTS_GTYPE_INTEGRATION
 
 #define COGL_GTYPE_TYPE_MATRIX (cogl_gtype_matrix_get_type ())

doc/reference/cogl-2.0-experimental/cogl-sections.txt

@@ -387,6 +387,7 @@ cogl_matrix_scale
 cogl_matrix_init_from_array
 cogl_matrix_get_array
 cogl_matrix_get_inverse
+cogl_matrix_is_identity
 </SECTION>
 
 <FILE>cogl-euler</FILE>

doc/reference/cogl/cogl-sections.txt

@@ -469,6 +469,7 @@ cogl_matrix_get_inverse
 cogl_matrix_transform_point
 cogl_matrix_project_points
 cogl_matrix_transform_points
+cogl_matrix_is_identity
 </SECTION>
 
 <SECTION>