1 files changed, 25 insertions, 0 deletions
diff --git a/util/transform.c b/util/transform.c
new file mode 100644
index 00000000..4cc725fd
--- /dev/null
+++ b/util/transform.c
@@ -0,0 +1,25 @@
+#include <wlr/util/transform.h>
+
+enum wl_output_transform wlr_output_transform_invert(
+		enum wl_output_transform tr) {
+	if ((tr & WL_OUTPUT_TRANSFORM_90) && !(tr & WL_OUTPUT_TRANSFORM_FLIPPED)) {
+		tr ^= WL_OUTPUT_TRANSFORM_180;
+	}
+	return tr;
+}
+
+enum wl_output_transform wlr_output_transform_compose(
+		enum wl_output_transform tr_a, enum wl_output_transform tr_b) {
+	uint32_t flipped = (tr_a ^ tr_b) & WL_OUTPUT_TRANSFORM_FLIPPED;
+	uint32_t rotation_mask = WL_OUTPUT_TRANSFORM_90 | WL_OUTPUT_TRANSFORM_180;
+	uint32_t rotated;
+	if (tr_b & WL_OUTPUT_TRANSFORM_FLIPPED) {
+		// When a rotation of k degrees is followed by a flip, the
+		// equivalent transform is a flip followed by a rotation of
+		// -k degrees.
+		rotated = (tr_b - tr_a) & rotation_mask;
+	} else {
+		rotated = (tr_a + tr_b) & rotation_mask;
+	}
+	return flipped | rotated;
+}