diff --git a/packages/ludic.render3d/env.ludic b/packages/ludic.render3d/env.ludic
index 7cb0008a..6ddb84aa 100644
--- a/packages/ludic.render3d/env.ludic
+++ b/packages/ludic.render3d/env.ludic
@@ -354,7 +354,7 @@ export state Render3dState {
   gvk_unpack_swap: bool = false     # GL_UNPACK_SWAP_BYTES: 16-bit PNG samples arrive big-endian
   gvk_st_buf: long = 0
   gvk_st_mem: long = 0
-  gvk_smp_keys: []string = null
+  gvk_smp_keys: []int = null        # 7 numbers per sampler: filters, wraps, compare, anisotropy, bias
   gvk_smp: []long = null
   gvk_buf: []long = null
   gvk_buf_mem: []long = null
diff --git a/packages/ludic.render3d/gpu_vk_draw.ludic b/packages/ludic.render3d/gpu_vk_draw.ludic
index c8a5b294..5908f633 100644
--- a/packages/ludic.render3d/gpu_vk_draw.ludic
+++ b/packages/ludic.render3d/gpu_vk_draw.ludic
@@ -1416,15 +1416,26 @@ function gvk_open(render3d_st: mut Render3dState, w: int, h: int, title: string)
   return true
 }
 
-# a program handle for a variant; the key is gpu_program's, so gpu_program_key works on both
+# A variant is made once and shared: a program is immutable here, so every actor asking for the
+# one it wants (actor.ludic, one per actor) gets the same handle, not its own modules and pipelines.
 function gvk_program_new(render3d_st: mut Render3dState, vs: string, fs: string, defines: string) -> int {
-  render3d_st.gvk_prog_counter += 1
-  let p = render3d_st.gvk_prog_counter
   let key = `{vs}|{fs}|{Text.replace(defines, "\n", ";")}`
   if render3d_st.gpu_prog_ids == null { render3d_st.gpu_prog_ids = new []int;  render3d_st.gpu_prog_keys = new []string }
+  for i in 0 .. len(render3d_st.gpu_prog_keys) {
+    if render3d_st.gpu_prog_keys[i] == key {
+      free(key)
+      return render3d_st.gpu_prog_ids[i]
+    }
+  }
+  render3d_st.gvk_prog_counter += 1
+  let p = render3d_st.gvk_prog_counter
   push(render3d_st.gpu_prog_ids, p)
   push(render3d_st.gpu_prog_keys, key)
-  if not gvk_program(render3d_st, p, key, render3d_st.gvk_spv_dir) { return 0 }
+  # a variant that cannot be made stays 0 for everyone who asks for it later
+  if not gvk_program(render3d_st, p, key, render3d_st.gvk_spv_dir) {
+    render3d_st.gpu_prog_ids[len(render3d_st.gpu_prog_ids) - 1] = 0
+    return 0
+  }
   return p
 }
 
diff --git a/packages/ludic.render3d/gpu_vk_res.ludic b/packages/ludic.render3d/gpu_vk_res.ludic
index 2bdccff3..b8357821 100644
--- a/packages/ludic.render3d/gpu_vk_res.ludic
+++ b/packages/ludic.render3d/gpu_vk_res.ludic
@@ -323,7 +323,7 @@ function gvk_tex_grow_mips(render3d_st: mut Render3dState, tex: int, w: int, h:
   let cb = gvk_once_begin(render3d_st)
   gvk_barrier(render3d_st, cb, old_image, false, 0, 1, layers, VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL, VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL)
   gvk_barrier(render3d_st, cb, render3d_st.gvk_tex_image[tex], false, 0, 1, layers, VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL, VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL)
-  let ic = bytes(VkImageCopy_sizeof)
+  let ic = gvk_tmp(render3d_st, VkImageCopy_sizeof)
   Vk.zero(ic, VkImageCopy_sizeof)
   Vk.put_i32(ic, VkImageCopy_srcSubresource + VkImageSubresourceLayers_aspectMask, VK_IMAGE_ASPECT_COLOR_BIT)
   Vk.put_i32(ic, VkImageCopy_srcSubresource + VkImageSubresourceLayers_layerCount, layers)
@@ -368,7 +368,7 @@ function gvk_tex_mips_into(render3d_st: mut Render3dState, cb: pointer, tex: int
     if dh < 1 { dh = 1 }
     gvk_barrier(render3d_st, cb, image, false, lv - 1, 1, layers, VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL, VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL)
     gvk_barrier(render3d_st, cb, image, false, lv, 1, layers, VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL, VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL)
-    let blit = bytes(VkImageBlit_sizeof)
+    let blit = gvk_tmp(render3d_st, VkImageBlit_sizeof)
     Vk.zero(blit, VkImageBlit_sizeof)
     Vk.put_i32(blit, VkImageBlit_srcSubresource + VkImageSubresourceLayers_aspectMask, VK_IMAGE_ASPECT_COLOR_BIT)
     Vk.put_i32(blit, VkImageBlit_srcSubresource + VkImageSubresourceLayers_mipLevel, lv - 1)
@@ -525,9 +525,16 @@ function gvk_tex_sampler(render3d_st: mut Render3dState, tex: int, min_f: int, m
 }
 function gvk_sampler(render3d_st: mut Render3dState, min_f: int, mag_f: int, wrap_s: int, wrap_t: int, compare: int, aniso: int) -> long {
   let bias = float_bits(gvk_mip_bias(render3d_st))
-  let key = `{min_f}/{mag_f}/{wrap_s}/{wrap_t}/{compare}/{aniso}/{bias}`
-  if render3d_st.gvk_smp_keys == null { render3d_st.gvk_smp_keys = new []string;  render3d_st.gvk_smp = new []long }
-  for i in 0 .. len(render3d_st.gvk_smp_keys) { if render3d_st.gvk_smp_keys[i] == key { return render3d_st.gvk_smp[i] } }
+  # looked up by the numbers themselves: a key string built on every call (and a texture read two
+  # ways in turn misses its own cache every time) was never given back
+  if render3d_st.gvk_smp_keys == null { render3d_st.gvk_smp_keys = new []int;  render3d_st.gvk_smp = new []long }
+  let ks = render3d_st.gvk_smp_keys
+  var i = 0
+  while i < len(render3d_st.gvk_smp) {
+    let o = i * 7
+    if ks[o] == min_f and ks[o + 1] == mag_f and ks[o + 2] == wrap_s and ks[o + 3] == wrap_t and ks[o + 4] == compare and ks[o + 5] == aniso and ks[o + 6] == bias { return render3d_st.gvk_smp[i] }
+    i += 1
+  }
   var mn = min_f
   if mn == 0 { mn = GL_NEAREST_MIPMAP_LINEAR }
   var mg = mag_f
@@ -563,7 +570,7 @@ function gvk_sampler(render3d_st: mut Render3dState, min_f: int, mag_f: int, wra
   let r = Vk.create_sampler(render3d_st.gvk_dev, sci, null, out)
   if r != VK_SUCCESS { gvk_fail(render3d_st, "vkCreateSampler", r);  return zero }
   let s = gvk_handle(out)
-  push(render3d_st.gvk_smp_keys, key)
+  push(ks, min_f);  push(ks, mag_f);  push(ks, wrap_s);  push(ks, wrap_t);  push(ks, compare);  push(ks, aniso);  push(ks, bias)
   push(render3d_st.gvk_smp, s)
   return s
 }