writefile: reuse SDNA between writes

Avoids decoding the SDNA string every undo step.

2 files changed, 30 insertions, 0 deletions

diff --git a/source/blender/makesdna/DNA_genfile.h b/source/blender/makesdna/DNA_genfile.h
index 27a3ff8f8cb..bc127ac2c82 100644
--- a/source/blender/makesdna/DNA_genfile.h
+++ b/source/blender/makesdna/DNA_genfile.h
@@ -80,6 +80,12 @@ struct SDNA *DNA_sdna_from_data(
         const char **r_error_message);
 void DNA_sdna_free(struct SDNA *sdna);
 
+/* Access for current Blender versions SDNA*/
+void               DNA_sdna_current_init(void);
+/* borrowed reference */
+const struct SDNA *DNA_sdna_current_get(void);
+void               DNA_sdna_current_free(void);
+
 int DNA_struct_find_nr_ex(const struct SDNA *sdna, const char *str, unsigned int *index_last);
 int DNA_struct_find_nr(const struct SDNA *sdna, const char *str);
 void DNA_struct_switch_endian(const struct SDNA *oldsdna, int oldSDNAnr, char *data);
diff --git a/source/blender/makesdna/intern/dna_genfile.c b/source/blender/makesdna/intern/dna_genfile.c
index f1d48c07de1..1e3c91d5ddc 100644
--- a/source/blender/makesdna/intern/dna_genfile.c
+++ b/source/blender/makesdna/intern/dna_genfile.c
@@ -605,6 +605,30 @@ SDNA *DNA_sdna_from_data(
 	}
 }
 
+/**
+ * Using globals is acceptable here, the data is read-only and only changes between Blender versions.
+ *
+ * So it is safe to create once and reuse.
+ */
+static SDNA *g_sdna = NULL;
+
+void DNA_sdna_current_init(void)
+{
+	g_sdna = DNA_sdna_from_data(DNAstr, DNAlen, false, false, NULL);
+}
+
+const struct SDNA *DNA_sdna_current_get(void)
+{
+	BLI_assert(g_sdna != NULL);
+	return g_sdna;
+}
+
+void DNA_sdna_current_free(void)
+{
+	DNA_sdna_free(g_sdna);
+	g_sdna = NULL;
+}
+
 /* ******************** END READ DNA ********************** */
 
 /* ******************* HANDLE DNA ***************** */