diff --git a/kubi-ui/src/backend/glium.rs b/kubi-ui/src/backend/glium.rs
index be55c95..8c886e4 100644
--- a/kubi-ui/src/backend/glium.rs
+++ b/kubi-ui/src/backend/glium.rs
@@ -48,8 +48,9 @@ impl BufferPair {
   }
 
   pub fn ensure_buffer_size(&mut self, need_vtx: usize, need_idx: usize) {
-    let current_vtx_size = self.vertex_buffer.get_size();
-    let current_idx_size = self.index_buffer.get_size();
+    let current_vtx_size = self.vertex_buffer.get_size() / std::mem::size_of::<Vertex>();
+    let current_idx_size = self.index_buffer.get_size() / std::mem::size_of::<u32>();
+    //log::debug!("current vtx size: {}, current idx size: {}", current_vtx_size, current_idx_size);
     if current_vtx_size >= need_vtx && current_idx_size >= need_idx {
       return
     }
@@ -84,9 +85,10 @@ impl BufferPair {
       return
     }
 
-    self.ensure_buffer_size(vtx.len(), idx.len());
-    self.vertex_buffer.slice_mut(0..vtx.len()).unwrap().write(vtx);
-    self.index_buffer.slice_mut(0..idx.len()).unwrap().write(idx);
+    self.ensure_buffer_size(self.vertex_count, self.index_count);
+
+    self.vertex_buffer.slice_mut(0..self.vertex_count).unwrap().write(vtx);
+    self.index_buffer.slice_mut(0..self.index_count).unwrap().write(idx);
   }
 
   pub fn is_empty(&self) -> bool {
diff --git a/kubi-ui/src/element.rs b/kubi-ui/src/element.rs
index 14916e5..c5023fc 100644
--- a/kubi-ui/src/element.rs
+++ b/kubi-ui/src/element.rs
@@ -6,10 +6,15 @@ use crate::{
   state::StateRepo
 };
 
-#[cfg(feature = "builtin_elements")] pub mod rect;
-#[cfg(feature = "builtin_elements")] pub mod container;
-#[cfg(feature = "builtin_elements")] pub mod spacer;
-#[cfg(feature = "builtin_elements")] pub mod progress_bar;
+#[cfg(feature = "builtin")] mod builtin {
+  pub mod rect;
+  pub mod container;
+  pub mod spacer;
+  pub mod progress_bar;
+}
+
+#[cfg(feature = "builtin")]
+pub use builtin::*;
 
 pub trait UiElement {
   fn name(&self) -> &'static str { "UiElement" }
diff --git a/kubi-ui/src/element/container.rs b/kubi-ui/src/element/builtin/container.rs
similarity index 96%
rename from kubi-ui/src/element/container.rs
rename to kubi-ui/src/element/builtin/container.rs
index 3346ce9..565b633 100644
--- a/kubi-ui/src/element/container.rs
+++ b/kubi-ui/src/element/builtin/container.rs
@@ -1,6 +1,13 @@
 use glam::{Vec2, vec2, Vec4};
-use crate::{UiDirection, LayoutInfo, draw::UiDrawCommand, measure::Response, state::StateRepo, UiSize};
-use super::UiElement;
+use crate::{
+  UiDirection,
+  UiSize,
+  LayoutInfo,
+  draw::UiDrawCommand,
+  measure::Response,
+  state::StateRepo,
+  element::UiElement
+};
 
 pub enum Alignment {
   Begin,
diff --git a/kubi-ui/src/element/progress_bar.rs b/kubi-ui/src/element/builtin/progress_bar.rs
similarity index 97%
rename from kubi-ui/src/element/progress_bar.rs
rename to kubi-ui/src/element/builtin/progress_bar.rs
index 854ad0b..3d54f95 100644
--- a/kubi-ui/src/element/progress_bar.rs
+++ b/kubi-ui/src/element/builtin/progress_bar.rs
@@ -3,9 +3,9 @@ use crate::{
   UiSize, LayoutInfo,
   draw::UiDrawCommand,
   measure::Response,
-  state::StateRepo
+  state::StateRepo,
+  element::UiElement
 };
-use super::UiElement;
 
 #[derive(Debug, Clone, Copy)]
 pub struct ProgressBar {
diff --git a/kubi-ui/src/element/rect.rs b/kubi-ui/src/element/builtin/rect.rs
similarity index 90%
rename from kubi-ui/src/element/rect.rs
rename to kubi-ui/src/element/builtin/rect.rs
index b998530..9838a24 100644
--- a/kubi-ui/src/element/rect.rs
+++ b/kubi-ui/src/element/builtin/rect.rs
@@ -1,6 +1,12 @@
 use glam::{vec2, Vec4};
-use crate::{state::StateRepo, LayoutInfo, measure::Response, draw::UiDrawCommand, UiSize};
-use super::UiElement;
+use crate::{
+  LayoutInfo,
+  UiSize,
+  element::UiElement,
+  state::StateRepo,
+  measure::Response,
+  draw::UiDrawCommand
+};
 
 pub struct Rect {
   pub size: (UiSize, UiSize),
diff --git a/kubi-ui/src/element/spacer.rs b/kubi-ui/src/element/builtin/spacer.rs
similarity index 80%
rename from kubi-ui/src/element/spacer.rs
rename to kubi-ui/src/element/builtin/spacer.rs
index 5b3bd77..92c4d61 100644
--- a/kubi-ui/src/element/spacer.rs
+++ b/kubi-ui/src/element/builtin/spacer.rs
@@ -1,6 +1,12 @@
 use glam::vec2;
-use crate::{state::StateRepo, LayoutInfo, measure::Response, draw::UiDrawCommand, UiDirection};
-use super::UiElement;
+use crate::{
+  LayoutInfo,
+  UiDirection,
+  element::UiElement,
+  state::StateRepo,
+  measure::Response,
+  draw::UiDrawCommand
+};
 
 pub struct Spacer(f32);