add move frame buttons

src/canvas_layer.cpp

@@ -228,10 +228,11 @@ bool Layer::create(int width, int height, std::string name)
     return true;
 }
 
-bool Layer::add_frame()
+bool Layer::add_frame(int index /*= -1*/)
 {
-    m_frames.emplace_back();
-    m_frames.back().create(w, h);
+    auto pos = index == -1 ? m_frames.end() : m_frames.begin() + index;
+    auto it = m_frames.emplace(pos);
+    it->create(w, h);
     frames_gpu_update();
     return true;
 }
@@ -267,6 +268,21 @@ void Layer::frames_gpu_update()
     });
 }
 
+int Layer::move_frame_offset(int frame, int offset) noexcept
+{
+    int new_pos = glm::clamp(frame + offset, 0, (int)m_frames.size() - 1);
+    auto from = m_frames.begin() + frame;
+    auto to = m_frames.begin() + new_pos;
+
+    if (new_pos < frame)
+        std::rotate(to, from, from + 1);
+    if (new_pos > frame)
+        std::rotate(from, from + 1, to + 1);
+
+    frames_gpu_update();
+    return new_pos;
+}
+
 int Layer::total_duration() const noexcept
 {
     int duration = 0;