fix(render3d): nothing draws into a BC7 texture - sampler binding binds, and compressed images get no mips

Metal aborted a net.sh guest ("MTLPixelFormatBC7_RGBAUnorm is not color renderable"): the crash
report's main thread was in vkQueueSubmit from gvk_once_end, MoltenVK encoding a vkCmdBlitImage
through a render pipeline. water.ludic bound its reflection by sampler name and then asked the
BOUND texture for mips - on Vulkan the bound texture was not the reflection but the last one
bound, since 23.3 a BC7 kit texture. gpu_bind_sampler now makes its texture the bound one, as
OpenGL did (and water binds it explicitly); gvk_tex_mips and gvk_mips_now skip compressed images;
gvk_pass_begin leaves out a compressed colour attachment and says so.

tests/net.sh passes (main e515bd87 built against it; host and guest agree on 196 animals, the
people, the board and the lost hiker).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

changes/render3d-bc-not-a-target.md

@@ -0,0 +1,9 @@
+bump: patch
+type: fix
+**A compressed texture is never drawn into.** On Vulkan, binding a texture to a sampler by name
+did not make it the bound texture, as it did on OpenGL, so a following `gpu_tex_param` or
+`gpu_tex_mips` acted on whatever was bound last. The water's reflection asked for its mip chain
+that way and, once kit textures came as BC7 (23.3), built one into a kit texture: MoltenVK blits
+through a render pass, and Metal aborted ("BC7 is not color renderable"). Binding for a sampler
+now binds, as OpenGL's did; mip generation leaves a compressed texture alone (its levels came with
+it); and a pass that would have a compressed image as a colour attachment leaves it out and says so.

packages/ludic.render3d/env.ludic

@@ -200,6 +200,7 @@ export state Render3dState {
   gvk_labels: bool = false          # R3D_VK_LABELS: each profiled pass is a debug label (Metal System Trace)
   gvk_inflight: int = -1
   gvk_nopool: bool = false
+  gvk_bc_said: int = 0              # attachments refused for being compressed, said so far
   gvk_has_bc: bool = false          # textureCompressionBC: .dds textures are uploaded compressed
   # R3D_VK_PROF: Vulkan objects made and destroyed, reported every 120 frames
   gvk_mk_img: int = 0

packages/ludic.render3d/gpu.ludic

@@ -608,6 +608,10 @@ function gpu_tex_free(render3d_st: mut Render3dState, tex: int) -> void {
 # a texture on a unit for a program's sampler, by the sampler's name
 function gpu_bind_sampler(render3d_st: mut Render3dState, prog: int, name: string, unit: int, kind: int, tex: int) -> void {
   gvk_bind_texture(render3d_st, prog, name, tex)
+  # as OpenGL's did, binding a texture for a sampler makes it the one a following gpu_tex_param or
+  # gpu_tex_mips acts on: render3d was written that way, and without it they reached whatever was
+  # bound last (a BC7 kit texture, which a mip blit then drew into)
+  if kind == GPU_TEX2D_ARRAY { render3d_st.gpu_bound_array = tex } else { render3d_st.gpu_bound_2d = tex }
 }
 
 # ---- render targets and passes -------------------------------------------------------------

packages/ludic.render3d/gpu_vk_draw.ludic

@@ -1094,10 +1094,29 @@ function gvk_pass_collect(render3d_st: mut Render3dState, fb: int, rec: words, r
   render3d_st.gvk_pass_dep[1] = rec[rec_o + 3]
 }
 
+# A block-compressed image cannot be drawn into (Metal aborts, "BC7 is not color renderable"):
+# an attachment that is one is dropped from the pass, and said, with what it was
+function gvk_pass_no_compressed(render3d_st: mut Render3dState) -> void {
+  var w = 0
+  for c in 0 .. render3d_st.gvk_pass_ncolor {
+    let tex = render3d_st.gvk_pass_col[c * 2]
+    if tex > 0 and tex < len(render3d_st.gvk_tex_glfmt) and gvk_is_compressed(render3d_st.gvk_tex_glfmt[tex]) {
+      if render3d_st.gvk_bc_said < 8 {
+        render3d_st.gvk_bc_said += 1
+        print(`r3d: vulkan: framebuffer {render3d_st.gvk_fb_cur} would draw into compressed texture {tex} ({gvk_tex_w(render3d_st, tex)}x{gvk_tex_h(render3d_st, tex)}); left out`)
+      }
+    } else {
+      render3d_st.gvk_pass_col[w * 2] = tex;  render3d_st.gvk_pass_col[w * 2 + 1] = render3d_st.gvk_pass_col[c * 2 + 1]
+      w += 1
+    }
+  }
+  render3d_st.gvk_pass_ncolor = w
+}
 function gvk_pass_begin(render3d_st: mut Render3dState, rec: words, rec_o: int) -> void {
   if render3d_st.gvk_in_pass { return }
   let cb = gvk_frame_cb(render3d_st)
   gvk_pass_collect(render3d_st, render3d_st.gvk_fb_cur, rec, rec_o)
+  gvk_pass_no_compressed(render3d_st)
   let aw = VkRenderingAttachmentInfo_sizeof
   let catt = gvk_tmp(render3d_st, aw * 3)
   Vk.zero(catt, aw * 3)
@@ -1818,6 +1837,7 @@ function gvk_resize_check(render3d_st: mut Render3dState) -> bool {
 # smallest level every frame): recorded into the open frame after its pass, so they cost no submit.
 # A chain that has to grow first still goes through its one-shot path.
 function gvk_mips_now(render3d_st: mut Render3dState, tex: int, w: int, h: int) -> void {
+  if gvk_is_compressed(render3d_st.gvk_tex_glfmt[tex]) { return }        # its levels came with it
   if render3d_st.gvk_cb == null or render3d_st.gvk_tex_levels[tex] <= 1 { gvk_flush(render3d_st);  gvk_tex_mips(render3d_st, tex, w, h);  return }
   gvk_pass_end(render3d_st)
   gvk_tex_mips_into(render3d_st, render3d_st.gvk_cb, tex, w, h)

packages/ludic.render3d/gpu_vk_res.ludic

@@ -356,6 +356,8 @@ function gvk_tex_grow_mips(render3d_st: mut Render3dState, tex: int, w: int, h:
 }
 
 function gvk_tex_mips(render3d_st: mut Render3dState, tex: int, w: int, h: int) -> bool {
+  # a block-compressed texture brought every level with it, and cannot be blitted into
+  if gvk_is_compressed(render3d_st.gvk_tex_glfmt[tex]) { return true }
   if render3d_st.gvk_tex_levels[tex] <= 1 and (w > 1 or h > 1) and not gvk_is_depth(render3d_st.gvk_tex_glfmt[tex]) {
     if not gvk_tex_grow_mips(render3d_st, tex, w, h) { return false }
   }

packages/ludic.render3d/water.ludic

@@ -324,6 +324,10 @@ function water_draw(render3d_st: mut Render3dState, depth_tex: int) -> void {
     # bind on its own unit first: generating the mip chain re-binds the texture on the active unit,
     # and it must not displace the depth texture the shader reads for the shore
     r3d_bind_2d(render3d_st, p, "u_refl", 1, render3d_st.water_refl.color);  ron = 1.0
+    # the parameter and the chain are the BOUND texture's, and binding a sampler by name does not
+    # bind it: without this they went to whatever was bound last - a BC7 kit texture since 23.3,
+    # which the mip blits then drew into (Metal: "BC7 is not color renderable")
+    gpu_tex_bind(render3d_st, GPU_TEX2D, render3d_st.water_refl.color)
     gpu_tex_param(render3d_st, GPU_TEX2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR)
     gpu_tex_mips(render3d_st, GPU_TEX2D)
   }