diff --git a/packages/ludic.render3d/env.ludic b/packages/ludic.render3d/env.ludic
index be8e2417..e5d2d485 100644
--- a/packages/ludic.render3d/env.ludic
+++ b/packages/ludic.render3d/env.ludic
@@ -382,6 +382,11 @@ export state Render3dState {
   gvk_buf_size: []int = null
   gvk_buf_map: []pointer = null      # host-visible buffers stay mapped for their whole life
   gvk_buf_used: []int = null         # the frame (gvk_frame_no) a draw last bound the buffer in
+  gvk_bsp_buf: []long = null         # per handle, a second buffer a re-filled one swaps with (gvk_buf_reserve)
+  gvk_bsp_mem: []long = null
+  gvk_bsp_size: []int = null
+  gvk_bsp_map: []pointer = null
+  gvk_bsp_used: []int = null
   gvk_frame_no: int = 1
   @max(4096) gvk_retired_buf: []long = null
   @max(4096) gvk_retired_mem: []long = null
diff --git a/packages/ludic.render3d/gpu_vk_res.ludic b/packages/ludic.render3d/gpu_vk_res.ludic
index 94b27e96..efa903eb 100644
--- a/packages/ludic.render3d/gpu_vk_res.ludic
+++ b/packages/ludic.render3d/gpu_vk_res.ludic
@@ -643,8 +643,11 @@ function gvk_buf_new(render3d_st: mut Render3dState) -> int {
   if render3d_st.gvk_buf == null {
     render3d_st.gvk_buf = new []long;  render3d_st.gvk_buf_mem = new []long;  render3d_st.gvk_buf_size = new []int;  render3d_st.gvk_buf_map = new []pointer
     render3d_st.gvk_buf_used = new []int;  render3d_st.gvk_retired_buf = new []long;  render3d_st.gvk_retired_mem = new []long
+    render3d_st.gvk_bsp_buf = new []long;  render3d_st.gvk_bsp_mem = new []long;  render3d_st.gvk_bsp_size = new []int
+    render3d_st.gvk_bsp_map = new []pointer;  render3d_st.gvk_bsp_used = new []int
     # handle 0 is "no buffer", as it is on OpenGL
     push(render3d_st.gvk_buf, zero);  push(render3d_st.gvk_buf_mem, zero);  push(render3d_st.gvk_buf_size, 0);  push(render3d_st.gvk_buf_map, null);  push(render3d_st.gvk_buf_used, 0)
+    gvk_bsp_grow(render3d_st)
   }
   # a handle a deleted buffer gave back first (gvk_buf_delete)
   if render3d_st.gvk_buf_spare != null and len(render3d_st.gvk_buf_spare) > 0 {
@@ -654,6 +657,7 @@ function gvk_buf_new(render3d_st: mut Render3dState) -> int {
     return b
   }
   push(render3d_st.gvk_buf, zero);  push(render3d_st.gvk_buf_mem, zero);  push(render3d_st.gvk_buf_size, 0);  push(render3d_st.gvk_buf_map, null);  push(render3d_st.gvk_buf_used, 0)
+  gvk_bsp_grow(render3d_st)
   return len(render3d_st.gvk_buf) - 1
 }
 
@@ -670,6 +674,7 @@ function gvk_buf_delete(render3d_st: mut Render3dState, b: int) -> void {
 }
 
 function gvk_buf_release(render3d_st: mut Render3dState, b: int) -> void {
+  gvk_bsp_drop(render3d_st, b)
   if render3d_st.gvk_buf[b] == 0 { return }
   let zero: long = 0
   if gvk_buf_busy(render3d_st, b) {
@@ -740,7 +745,15 @@ function gvk_buf_reserve(render3d_st: mut Render3dState, b: int, n: int) -> bool
   if b <= 0 or b >= len(render3d_st.gvk_buf) { return false }
   # already big enough, and no draw this frame reads what is there: fill it in place
   if render3d_st.gvk_buf[b] != 0 and render3d_st.gvk_buf_size[b] >= n and (not gvk_buf_busy(render3d_st, b) or gvk_buf_is_gpu(render3d_st, b)) { return true }
-  gvk_buf_release(render3d_st, b)
+  # big enough but read by a frame still on the GPU: its second buffer, when that one is free, and
+  # else the busy one becomes the second and a new one is made - a buffer re-filled every frame (the
+  # interface's vertices) ping-pongs between two, where it was made and destroyed every frame
+  if render3d_st.gvk_buf[b] != 0 and render3d_st.gvk_buf_size[b] >= n {
+    if gvk_bsp_swap(render3d_st, b, n) { return true }
+    gvk_bsp_park(render3d_st, b)
+  } else {
+    gvk_buf_release(render3d_st, b)
+  }
   var size = n
   if size < 64 { size = 64 }
   let size_l: long = size
@@ -853,3 +866,65 @@ function gvk_prime_tables(render3d_st: mut Render3dState) -> void {
   let none: long = 0
   for i in 0 .. GVK_PRIME_MAX { push(hs, none) }
 }
+
+# ---- a re-filled buffer's second: gvk_buf_reserve swaps to it while the first is still being read ----
+@alloc_ok("one slot per buffer handle, beside the handle's own (gvk_buf_new)")
+function gvk_bsp_grow(render3d_st: mut Render3dState) -> void {
+  let zero: long = 0
+  push(render3d_st.gvk_bsp_buf, zero)
+  push(render3d_st.gvk_bsp_mem, zero)
+  push(render3d_st.gvk_bsp_size, 0)
+  push(render3d_st.gvk_bsp_map, null)
+  push(render3d_st.gvk_bsp_used, 0)
+}
+function gvk_bsp_busy(render3d_st: Render3dState, b: int) -> bool {
+  let u = render3d_st.gvk_bsp_used[b]
+  return u == render3d_st.gvk_frame_no or (render3d_st.gvk_frame_pending and u == render3d_st.gvk_frame_pending_no)
+}
+# the second in place of the first when it is there, big enough and read by nothing still running
+function gvk_bsp_swap(render3d_st: mut Render3dState, b: int, n: int) -> bool {
+  if render3d_st.gvk_bsp_buf == null or b >= len(render3d_st.gvk_bsp_buf) { return false }
+  if render3d_st.gvk_bsp_buf[b] == 0 or render3d_st.gvk_bsp_size[b] < n or gvk_bsp_busy(render3d_st, b) { return false }
+  let tb = render3d_st.gvk_buf[b]
+  let tm = render3d_st.gvk_buf_mem[b]
+  let ts = render3d_st.gvk_buf_size[b]
+  let tp = render3d_st.gvk_buf_map[b]
+  let tu = render3d_st.gvk_buf_used[b]
+  render3d_st.gvk_buf[b] = render3d_st.gvk_bsp_buf[b];  render3d_st.gvk_buf_mem[b] = render3d_st.gvk_bsp_mem[b]
+  render3d_st.gvk_buf_size[b] = render3d_st.gvk_bsp_size[b];  render3d_st.gvk_buf_map[b] = render3d_st.gvk_bsp_map[b]
+  render3d_st.gvk_buf_used[b] = render3d_st.gvk_bsp_used[b]
+  render3d_st.gvk_bsp_buf[b] = tb;  render3d_st.gvk_bsp_mem[b] = tm;  render3d_st.gvk_bsp_size[b] = ts
+  render3d_st.gvk_bsp_map[b] = tp;  render3d_st.gvk_bsp_used[b] = tu
+  return true
+}
+# the busy first becomes the second (the old second let go), leaving the handle empty for a new one
+function gvk_bsp_park(render3d_st: mut Render3dState, b: int) -> void {
+  let zero: long = 0
+  gvk_bsp_drop(render3d_st, b)
+  render3d_st.gvk_bsp_buf[b] = render3d_st.gvk_buf[b];  render3d_st.gvk_bsp_mem[b] = render3d_st.gvk_buf_mem[b]
+  render3d_st.gvk_bsp_size[b] = render3d_st.gvk_buf_size[b];  render3d_st.gvk_bsp_map[b] = render3d_st.gvk_buf_map[b]
+  render3d_st.gvk_bsp_used[b] = render3d_st.gvk_buf_used[b]
+  render3d_st.gvk_buf[b] = zero;  render3d_st.gvk_buf_mem[b] = zero;  render3d_st.gvk_buf_size[b] = 0
+  render3d_st.gvk_buf_map[b] = null;  render3d_st.gvk_buf_used[b] = 0
+}
+# the second let go: destroyed now, or retired until the frame that read it has finished
+function gvk_bsp_drop(render3d_st: mut Render3dState, b: int) -> void {
+  if render3d_st.gvk_bsp_buf == null or b >= len(render3d_st.gvk_bsp_buf) or render3d_st.gvk_bsp_buf[b] == 0 { return }
+  let zero: long = 0
+  if gvk_bsp_busy(render3d_st, b) {
+    @alloc_ok("within the retire lists' room made at start-up (@max 4096)")
+    push(render3d_st.gvk_retired_buf, render3d_st.gvk_bsp_buf[b])
+    @alloc_ok("within the retire lists' room made at start-up (@max 4096)")
+    push(render3d_st.gvk_retired_mem, render3d_st.gvk_bsp_mem[b])
+    @alloc_ok("within the retire lists' room made at start-up (@max 4096)")
+    while len(render3d_st.gvk_retired_frame) < len(render3d_st.gvk_retired_buf) - 1 { push(render3d_st.gvk_retired_frame, 0) }
+    @alloc_ok("within the retire lists' room made at start-up (@max 4096)")
+    push(render3d_st.gvk_retired_frame, render3d_st.gvk_bsp_used[b])
+  } else {
+    render3d_st.gvk_mk_x_buf += 1
+    Vk.destroy_buffer(render3d_st.gvk_dev, render3d_st.gvk_bsp_buf[b], render3d_st.gvk_ac)
+    gvk_mem_free(render3d_st, gvk_mem_id(render3d_st.gvk_bsp_mem[b]))
+  }
+  render3d_st.gvk_bsp_buf[b] = zero;  render3d_st.gvk_bsp_mem[b] = zero;  render3d_st.gvk_bsp_size[b] = 0
+  render3d_st.gvk_bsp_map[b] = null;  render3d_st.gvk_bsp_used[b] = 0
+}