libobs/util: Add funcs to push zeroed data to circlebufs

Adds circlebuf_push_front_zero and circlebuf_push_back_zero to
conveniently push zeroed data to the front/back of the buffer without
having to create an intermediary buffer to accomplish the same thing.

docs/sphinx/reference-libobs-util-circlebuf.rst

@@ -91,6 +91,24 @@ Circular Buffer Inline Functions
 
 ---------------------
 
+.. function:: void circlebuf_push_back_zero(struct circlebuf *cb, size_t size)
+
+   Pushes zeroed data to the end of the circular buffer.
+
+   :param cb:       The circular buffer
+   :param size:     Size
+
+---------------------
+
+.. function:: void circlebuf_push_front_zero(struct circlebuf *cb, size_t size)
+
+   Pushes zeroed data to the front of the circular buffer.
+
+   :param cb:       The circular buffer
+   :param size:     Size
+
+---------------------
+
 .. function:: void circlebuf_peek_front(struct circlebuf *cb, void *data, size_t size)
 
    Peeks data at the front of the circular buffer.

libobs/util/circlebuf.h

@@ -189,6 +189,48 @@ static inline void circlebuf_push_front(struct circlebuf *cb, const void *data,
 	}
 }
 
+static inline void circlebuf_push_back_zero(struct circlebuf *cb, size_t size)
+{
+	size_t new_end_pos = cb->end_pos + size;
+
+	cb->size += size;
+	circlebuf_ensure_capacity(cb);
+
+	if (new_end_pos > cb->capacity) {
+		size_t back_size = cb->capacity - cb->end_pos;
+		size_t loop_size = size - back_size;
+
+		if (back_size)
+			memset((uint8_t*)cb->data + cb->end_pos, 0, back_size);
+		memset(cb->data, 0, loop_size);
+
+		new_end_pos -= cb->capacity;
+	} else {
+		memset((uint8_t*)cb->data + cb->end_pos, 0, size);
+	}
+
+	cb->end_pos = new_end_pos;
+}
+
+static inline void circlebuf_push_front_zero(struct circlebuf *cb, size_t size)
+{
+	cb->size += size;
+	circlebuf_ensure_capacity(cb);
+
+	if (cb->start_pos < size) {
+		size_t back_size = size - cb->start_pos;
+
+		if (cb->start_pos)
+			memset(cb->data, 0, cb->start_pos);
+
+		cb->start_pos = cb->capacity - back_size;
+		memset((uint8_t*)cb->data + cb->start_pos, 0, back_size);
+	} else {
+		cb->start_pos -= size;
+		memset((uint8_t*)cb->data + cb->start_pos, 0, size);
+	}
+}
+
 static inline void circlebuf_peek_front(struct circlebuf *cb, void *data,
 		size_t size)
 {