Cache compiles in the macOS build script, including Xcode builds (#16553)

# Description

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> Please provide a summary of the changes made in this PR. Include
details such as:
  > * What issue does this PR address or fix?
  > * What new features or enhancements does this PR introduce?
> * Are there any breaking changes or dependencies that need to be
considered?
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Windows traditionally limits many file operations to `MAX_PATH` (260
characters). Deeply nested plugin packages can exceed this limit during
`.whl` extraction, leaving files missing and causing the plugin to fail
to load.

This change adds a shared extended_path helper that prepares paths for
Windows file operations using the extended-length prefixes `\\?\` or
`\\?\UNC\`. The helper is used for ZIP archive I/O and extraction
destinations, including plugin wheel extraction. This avoids relying on
the Windows long-path setting, which changes machine-wide settings.

Paths remain unprefixed outside file operations. Code that bypasses the
shared ZIP helpers may still require separate long-path handling.

See [Microsoft's documentation on path length
limitation](https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation?tabs=registry)

# Screenshots/Recordings/Graphs

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> Please attach relevant screenshots to showcase the UI changes.
> Please attach images that can help explain the changes.
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## Tests

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> Please describe the tests that you have conducted to verify the
changes made in this PR.
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Tested on Windows 11 by using a portable installation of OrcaSlicer and
placing it in some really long filepath length e.g.
`C:/somename/<240 characters long folder path>/OrcaSlicer` and then
running and trying to install any plugin locally or on OrcaCloud.

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> A guide for users on how to download the artifacts from this PR.
-->

[How to Download Pull Requests Artifacts for
Testing](https://www.orcaslicer.com/wiki/how_to_download_pr_artifacts)

CMakeLists.txt

@@ -288,6 +288,19 @@ if (APPLE)
     # Type"); Ninja/-Wall does not, and under -Werror it fails Xcode builds on code CI accepts.
     set(CMAKE_XCODE_ATTRIBUTE_GCC_WARN_64_TO_32_BIT_CONVERSION "NO")
 
+    # The Xcode generator ignores CMAKE_<LANG>_COMPILER_LAUNCHER, so hand the launcher to
+    # Xcode's own Compiler Launcher setting, which wraps every clang compile (C, C++,
+    # Objective-C++ and the precompiled header) with one program: the C++ launcher wins when
+    # both are set. The setting takes a single program path, not a CMake launcher list.
+    # Xcode versions without it ignore it and build uncached.
+    if (CMAKE_GENERATOR STREQUAL "Xcode")
+        if (CMAKE_CXX_COMPILER_LAUNCHER)
+            set(CMAKE_XCODE_ATTRIBUTE_C_COMPILER_LAUNCHER "${CMAKE_CXX_COMPILER_LAUNCHER}")
+        elseif (CMAKE_C_COMPILER_LAUNCHER)
+            set(CMAKE_XCODE_ATTRIBUTE_C_COMPILER_LAUNCHER "${CMAKE_C_COMPILER_LAUNCHER}")
+        endif ()
+    endif ()
+
     message(STATUS "Orca: IS_CROSS_COMPILE: ${IS_CROSS_COMPILE}")
 elseif (CMAKE_SYSTEM_NAME STREQUAL "Linux")
     set(CMAKE_INSTALL_RPATH "$ORIGIN")

build_release_macos.sh

@@ -111,6 +111,54 @@ else
   export CMAKE_POLICY_COMPAT=""
 fi
 
+# Compiler cache, as in build_linux.sh. The program comes from CMAKE_CCACHE, else from a
+# launcher already set in the environment (the CI build sets ccache there), else sccache or
+# ccache from PATH; one program serves both languages. Each run applies its own choice to the
+# build directories, replacing a launcher an earlier run or a hand-run configure recorded.
+CMAKE_CCACHE_ARGS=()
+CCACHE_VAR=""
+for var in CMAKE_CCACHE CMAKE_CXX_COMPILER_LAUNCHER CMAKE_C_COMPILER_LAUNCHER; do
+    if [ -n "${!var:-}" ]; then
+        CCACHE_VAR=$var
+        break
+    fi
+done
+if [ -n "$CCACHE_VAR" ]; then
+    CCACHE_PROGRAM=${!CCACHE_VAR}
+    echo "Checking ${CCACHE_VAR} environment variable for compiler cache program..."
+    CMAKE_CCACHE=$(command -v "${CCACHE_PROGRAM}") || {
+        echo "${CCACHE_VAR} environment variable is set to '${CCACHE_PROGRAM}' but it was not found in PATH."
+        CMAKE_CCACHE=""
+    }
+elif command -v sccache >/dev/null 2>&1 ; then
+    CMAKE_CCACHE=$(command -v sccache)
+elif command -v ccache >/dev/null 2>&1 ; then
+    CMAKE_CCACHE=$(command -v ccache)
+fi
+if [ -n "${CMAKE_CCACHE}" ] ; then
+    echo "${CMAKE_CCACHE} found, enabling compiler caching..."
+    CMAKE_CCACHE_ARGS=(-DCMAKE_C_COMPILER_LAUNCHER="${CMAKE_CCACHE}" -DCMAKE_CXX_COMPILER_LAUNCHER="${CMAKE_CCACHE}")
+    # The same ccache settings as the CI build. Without this sloppiness ccache refuses every
+    # compile that uses the precompiled header, which is most of OrcaSlicer, and skips headers
+    # a checkout has just written. It is added to the sloppiness already configured, and
+    # CCACHE_SLOPPINESS or CCACHE_(NO)DEPEND set in the environment win.
+    if [[ "$(basename "${CMAKE_CCACHE}")" == ccache ]] ; then
+        if [[ -z "${CCACHE_SLOPPINESS+x}" ]] ; then
+            CCACHE_SLOPPINESS=$("${CMAKE_CCACHE}" --get-config sloppiness 2>/dev/null || true)
+            export CCACHE_SLOPPINESS="${CCACHE_SLOPPINESS:+${CCACHE_SLOPPINESS},}pch_defines,time_macros,include_file_mtime,include_file_ctime"
+        fi
+        # Hash the includes the compiler reports instead of preprocessing every miss.
+        if [[ -z "${CCACHE_DEPEND+x}${CCACHE_NODEPEND+x}" ]] ; then
+            export CCACHE_DEPEND=1
+        fi
+    fi
+else
+    echo "Note: ccache or sccache are not found. Install either of them for faster rebuilds."
+    # Clear a launcher recorded by an earlier configure. The entries must be set empty rather
+    # than removed: CMake fills a missing launcher entry from the environment.
+    CMAKE_CCACHE_ARGS=(-DCMAKE_C_COMPILER_LAUNCHER:STRING= -DCMAKE_CXX_COMPILER_LAUNCHER:STRING=)
+fi
+
 echo "Build params:"
 echo " - ARCH: $ARCH"
 echo " - BUILD_CONFIG: $BUILD_CONFIG"
@@ -162,6 +210,7 @@ function build_deps() {
                         -DCMAKE_OSX_ARCHITECTURES:STRING="${_ARCH}" \
                         -DCMAKE_OSX_DEPLOYMENT_TARGET="${OSX_DEPLOYMENT_TARGET}" \
                         -DCMAKE_IGNORE_PREFIX_PATH="${CMAKE_IGNORE_PREFIX_PATH}" \
+                        "${CMAKE_CCACHE_ARGS[@]}" \
                         ${CMAKE_POLICY_COMPAT}
                 fi
                 cmake --build . --config "$BUILD_CONFIG" --target deps
@@ -264,6 +313,7 @@ function build_slicer() {
                     -DCMAKE_OSX_ARCHITECTURES="${_ARCH}" \
                     -DCMAKE_OSX_DEPLOYMENT_TARGET="${OSX_DEPLOYMENT_TARGET}" \
                     -DCMAKE_IGNORE_PREFIX_PATH="${CMAKE_IGNORE_PREFIX_PATH}" \
+                    "${CMAKE_CCACHE_ARGS[@]}" \
                     ${CMAKE_POLICY_COMPAT}
             fi
             cmake --build . --config "$BUILD_CONFIG" --target "$SLICER_BUILD_TARGET"

src/libslic3r/PNGReadWrite.cpp

@@ -211,6 +211,35 @@ bool decode_colored_png(const ReadBuf &in_buf, ImageColorscale &out_img)
     return decode_colored_png(stream, out_img);
 }
 
+bool is_decodable_8bit_png(const ReadBuf &pngbuf)
+{
+    static const constexpr int PNG_SIG_BYTES = 8;
+
+    struct ReadBufStream stream{pngbuf};
+    std::vector<png_byte> sig(PNG_SIG_BYTES, 0);
+    stream.read(sig.data(), PNG_SIG_BYTES);
+    if (!png_check_sig(sig.data(), PNG_SIG_BYTES))
+        return false;
+
+    PNGDescr dsc;
+    dsc.png = png_create_read_struct(PNG_LIBPNG_VER_STRING, nullptr, nullptr, nullptr);
+    if (!dsc.png)
+        return false;
+    dsc.info = png_create_info_struct(dsc.png);
+    if (!dsc.info)
+        return false;
+
+    if (!png_read_header_guarded(dsc.png, dsc.info, &stream, PNG_SIG_BYTES))
+        return false;
+
+    const size_t color_type = png_get_color_type(dsc.png, dsc.info);
+    const size_t bit_depth  = png_get_bit_depth(dsc.png, dsc.info);
+    const bool   grey       = color_type == PNG_COLOR_TYPE_GRAY;
+    const bool   colour     = color_type == PNG_COLOR_TYPE_RGB || color_type == PNG_COLOR_TYPE_RGB_ALPHA;
+    return png_get_image_width(dsc.png, dsc.info) > 0 && png_get_image_height(dsc.png, dsc.info) > 0 &&
+           bit_depth == 8 && (grey || colour);
+}
+
 
 // Down to earth function to store a packed RGB image to file. Mostly useful for debugging purposes.
 // Based on https://www.lemoda.net/c/write-png/

src/libslic3r/PNGReadWrite.hpp

@@ -50,6 +50,9 @@ struct ReadBuf { const void *buf = nullptr; const size_t sz = 0; };
 
 bool is_png(const ReadBuf &pngbuf);
 
+// True if decode_png() or decode_colored_png() would accept these bytes, judged from the header alone.
+bool is_decodable_8bit_png(const ReadBuf &pngbuf);
+
 struct ReadBufStream: public IStream {
     const ReadBuf &rbuf_ref;
     size_t pos = 0;

src/libslic3r/TextureDisplacement.cpp

@@ -283,7 +283,7 @@ bool height_texture_has_color(const TextureDisplacementLayer &layer)
     return decode_height_texture(layer).has_color();
 }
 
-DecodedHeightTexture decode_height_texture(const TextureDisplacementLayer &layer)
+DecodedHeightTexture decode_height_texture(const TextureDisplacementLayer &layer, bool keep_decoded)
 {
     DecodedHeightTexture result;
     if (layer.empty())
@@ -351,13 +351,15 @@ DecodedHeightTexture decode_height_texture(const TextureDisplacementLayer &layer
                 }
         }
 
-        std::lock_guard<std::mutex> lock(g_decoded_texture_cache.mutex);
-        // Opportunistically drop entries for image_data that no longer exists anywhere, so the
-        // cache doesn't grow without bound across many add/remove-texture cycles in a long session.
-        auto &entries = g_decoded_texture_cache.entries;
-        for (auto it = entries.begin(); it != entries.end();)
-            it = it->second.first.expired() ? entries.erase(it) : std::next(it);
-        entries[key] = { std::weak_ptr<const std::vector<unsigned char>>(layer.image_data), result };
+        if (keep_decoded) {
+            std::lock_guard<std::mutex> lock(g_decoded_texture_cache.mutex);
+            // Opportunistically drop entries for image_data that no longer exists anywhere, so the
+            // cache doesn't grow without bound across many add/remove-texture cycles in a long session.
+            auto &entries = g_decoded_texture_cache.entries;
+            for (auto it = entries.begin(); it != entries.end();)
+                it = it->second.first.expired() ? entries.erase(it) : std::next(it);
+            entries[key] = { std::weak_ptr<const std::vector<unsigned char>>(layer.image_data), result };
+        }
     }
 
     // The image-adjustment panel's live edits, on top of the decode and before the smoothing. Before,

src/libslic3r/TextureDisplacement.hpp

@@ -599,8 +599,9 @@ DecodedHeightTexture downscale_height_texture(const DecodedHeightTexture &src, i
 // colour PNGs are accepted; for a colour source the height is its luminance, using the same
 // coefficients wxImage::ConvertToGreyscale() uses, so a texture imported as colour displaces exactly
 // as it did when the importer flattened it to grey on the way in. Returns an empty
-// DecodedHeightTexture if image_data is empty or is not a PNG at all.
-DecodedHeightTexture decode_height_texture(const TextureDisplacementLayer &layer);
+// DecodedHeightTexture if image_data is empty or is not a PNG at all. keep_decoded = false leaves the
+// result out of the decode cache, for one-off reads such as a picker thumbnail that must not hold full-size pixels.
+DecodedHeightTexture decode_height_texture(const TextureDisplacementLayer &layer, bool keep_decoded = true);
 
 // decode_height_texture(layer).has_color(), answered from the decode cache rather than from a copy of the
 // texture - cheap enough to ask every frame. Smoothing does not change it, so the raw decode is what is read.

src/libslic3r/Utils.hpp

@@ -842,6 +842,13 @@ void load_string_file(const boost::filesystem::path& p, std::string& str);
 
 bool check_layer_id_pattern(const std::string& pattern, int layer_id);
 
+// On Windows, return an equivalent path carrying the extended-length ("\\?\" / "\\?\UNC\")
+// prefix so the Win32 APIs accept it past MAX_PATH even when LongPathsEnabled is off. The path
+// is made absolute and lexically normalized first, because the prefix disables normalisation.
+// A path that is already extended (or a device path) is returned unchanged; on other platforms,
+// or when an absolute path cannot be formed, the input is returned unchanged.
+boost::filesystem::path extended_path(const boost::filesystem::path& path);
+
 } // namespace Slic3r
 
 #if WIN32

src/libslic3r/miniz_extension.cpp

@@ -17,6 +17,7 @@
 
 #if defined(_MSC_VER) || defined(__MINGW64__)
 #include "boost/nowide/cstdio.hpp"
+#include "boost/nowide/convert.hpp"
 #endif
 
 #include "I18N.hpp"
@@ -62,7 +63,11 @@ bool open_zip(mz_zip_archive *zip, const char *fname, bool isread)
 
     FILE *f = nullptr;
 #if defined(_MSC_VER) || defined(__MINGW64__)
-    f = boost::nowide::fopen(fname, mode);
+    // fname is UTF-8 (the nowide contract). Route it through the shared extended-path helper so an
+    // archive stored past MAX_PATH opens even with LongPathsEnabled off.
+    const std::wstring wide_path = boost::nowide::widen(fname);
+    const std::string  extended  = boost::nowide::narrow(Slic3r::extended_path(boost::filesystem::path(wide_path)).wstring());
+    f = boost::nowide::fopen(extended.c_str(), mode);
 #elif defined(__GNUC__) && defined(_LARGEFILE64_SOURCE)
     f = fopen64(fname, mode);
 #else
@@ -101,6 +106,14 @@ bool close_zip(mz_zip_archive *zip, bool isread)
     }
     return ret;
 }
+
+#ifdef WIN32
+// mz_file_write_func writing an extracted entry into an already-open FILE*.
+size_t mz_write_to_cfile(void *opaque, mz_uint64 /*file_ofs*/, const void *buffer, size_t size)
+{
+    return std::fwrite(buffer, 1, size, static_cast<FILE *>(opaque));
+}
+#endif
 }
 
 bool open_zip_reader(mz_zip_archive *zip, const std::string &fname)
@@ -116,6 +129,36 @@ bool open_zip_writer(mz_zip_archive *zip, const std::string &fname)
 bool close_zip_reader(mz_zip_archive *zip) { return close_zip(zip, true); }
 bool close_zip_writer(mz_zip_archive *zip) { return close_zip(zip, false); }
 
+bool extract_zip_entry_to_file(mz_zip_archive *zip, mz_uint file_index, const boost::filesystem::path &dest_path)
+{
+    if (!zip)
+        return false;
+#ifdef WIN32
+    // Open the destination ourselves with a Windows extended-length path: miniz's narrow
+    // extract_to_file cannot be relied on past MAX_PATH with LongPathsEnabled off, and its wide
+    // variant takes a plain (unprefixed) path and a text-mode stream. This keeps the write binary.
+    FILE *file = ::_wfopen(Slic3r::extended_path(dest_path).wstring().c_str(), L"wb");
+    if (!file) {
+        zip->m_last_error = MZ_ZIP_FILE_OPEN_FAILED;
+        return false;
+    }
+
+    const bool written = mz_zip_reader_extract_to_callback(zip, file_index, mz_write_to_cfile, file, 0) != 0;
+    const bool closed  = std::fclose(file) == 0;
+    if (!written || !closed) {
+        if (written && !closed)
+            zip->m_last_error = MZ_ZIP_FILE_CLOSE_FAILED;
+        // Drop the partial entry rather than leave a truncated file behind.
+        boost::system::error_code ec;
+        boost::filesystem::remove(Slic3r::extended_path(dest_path), ec);
+        return false;
+    }
+    return true;
+#else
+    return mz_zip_reader_extract_to_file(zip, file_index, dest_path.string().c_str(), 0) != 0;
+#endif
+}
+
 std::string decode_archive_entry_path(mz_zip_archive *zip, const mz_zip_archive_file_stat &stat)
 {
     if (stat.m_is_utf8)
@@ -156,10 +199,13 @@ bool extract_archive_confined(const std::string &zip_path_utf8, const std::strin
         }
         const std::string dest_file = dest_dir + "/" + stat.m_filename;
         try {
+            // Use the extended-length form for every filesystem call so entries under a destination
+            // past MAX_PATH are created even with LongPathsEnabled off.
+            const boost::filesystem::path dest_path(dest_file);
+            const boost::filesystem::path io_dest = extended_path(dest_path);
             if (stat.m_is_directory) {
-                const boost::filesystem::path dest_path(dest_file);
-                if (!boost::filesystem::exists(dest_path))
-                    boost::filesystem::create_directories(dest_path);
+                if (!boost::filesystem::exists(io_dest))
+                    boost::filesystem::create_directories(io_dest);
                 continue;
             }
             if (stat.m_uncomp_size == 0) {
@@ -167,10 +213,9 @@ bool extract_archive_confined(const std::string &zip_path_utf8, const std::strin
                 continue;
             }
             // Replace a symlink at the destination rather than writing through it.
-            const boost::filesystem::path dest_path(dest_file);
-            if (boost::filesystem::is_symlink(boost::filesystem::symlink_status(dest_path)))
-                boost::filesystem::remove(dest_path);
-            if (!mz_zip_reader_extract_to_file(&archive, stat.m_file_index, dest_file.c_str(), 0)) {
+            if (boost::filesystem::is_symlink(boost::filesystem::symlink_status(io_dest)))
+                boost::filesystem::remove(io_dest);
+            if (!extract_zip_entry_to_file(&archive, stat.m_file_index, dest_path)) {
                 BOOST_LOG_TRIVIAL(error) << "Unzip: extract file " << stat.m_filename << " to dest " << dest_file << " failed";
                 close_zip_reader(&archive);
                 return false;

src/libslic3r/miniz_extension.hpp

@@ -1,6 +1,7 @@
 #ifndef MINIZ_EXTENSION_HPP
 #define MINIZ_EXTENSION_HPP
 
+#include <boost/filesystem/path.hpp>
 #include <string>
 #include <miniz.h>
 
@@ -13,6 +14,10 @@ bool close_zip_writer(mz_zip_archive *zip);
 std::string decode_archive_entry_path(mz_zip_archive *zip, const mz_zip_archive_file_stat &stat);
 // Extracts every entry of the archive under dest_dir. Nothing is written if any entry would resolve outside dest_dir.
 bool extract_archive_confined(const std::string &zip_path_utf8, const std::string &dest_dir);
+// Extracts one entry into dest_path, binary-safe and overwriting. On Windows the destination is
+// opened through an extended-length path so it works past MAX_PATH even with LongPathsEnabled off;
+// a partial file is removed if the write fails. False for a directory/unsupported entry or on error.
+bool extract_zip_entry_to_file(mz_zip_archive *zip, mz_uint file_index, const boost::filesystem::path &dest_path);
 
 class MZ_Archive {
 public:

src/libslic3r/utils.cpp

@@ -2254,5 +2254,45 @@ bool check_layer_id_pattern(const std::string& pattern, int layer_id){
     return mod >= 0 && mod < count;
 }
 
+boost::filesystem::path extended_path(const boost::filesystem::path& path) {
+#ifdef WIN32
+    namespace fs = boost::filesystem;
+
+    // Already extended, or an explicit device path (which is not subject to MAX_PATH and must not
+    // be absolutized or normalized): leave it alone.
+    {
+        fs::path prefix_candidate = path;
+        const std::wstring native = prefix_candidate.make_preferred().wstring();
+        if (native.rfind(L"\\\\?\\", 0) == 0 || native.rfind(L"\\\\.\\", 0) == 0)
+            return fs::path(native);
+    }
+
+    fs::path absolute = path;
+    if (!absolute.is_absolute()) {
+        boost::system::error_code ec;
+        absolute = fs::absolute(absolute, ec);
+        if (ec)
+            return path; // can't form a valid prefixed path from a relative one
+    }
+
+    // A trailing separator is redundant to the Win32 APIs, but lexically_normal() would rewrite it
+    // as a "." element, which the "\\?\" prefix (normalisation off) takes literally. Drop it first.
+    while (absolute.has_relative_path() && absolute.filename() == ".")
+        absolute = absolute.parent_path();
+
+    // The "\\?\" prefix turns off Win32 normalisation, so do it here first.
+    absolute = absolute.lexically_normal();
+
+    // Extended paths only recognize backslash separators.
+    const std::wstring native = absolute.make_preferred().wstring();
+    if (native.empty())
+        return path;
+    if (native.rfind(L"\\\\", 0) == 0)
+        return fs::path(L"\\\\?\\UNC\\" + native.substr(2)); // \\server\share\... -> \\?\UNC\server\share\...
+    return fs::path(L"\\\\?\\" + native);                    // C:\dir\... -> \\?\C:\dir\...
+#else
+    return path;
+#endif
+}
 
 }; // namespace Slic3r

src/slic3r/GUI/Gizmos/GLGizmoTextureDisplacement.cpp

@@ -174,6 +174,10 @@ constexpr int HEIGHT_TEX_MAX_PX = 2048;
 // The full-size image is only ever adjusted once, on commit.
 constexpr int ADJUST_PREVIEW_MAX_PX = 384;
 
+// Library textures the texture picker decodes per frame. Each decode runs on the GUI thread, so the
+// rest of the visible tiles fill in over the following frames instead of in one stall.
+constexpr int PICKER_LOADS_PER_FRAME = 2;
+
 // How many rings of vertex-adjacent triangles either side of the paint's edge join the border refine
 // band (see collect_paint_region()). Two is enough to grade the size change without the band's own
 // cost growing to matter: it is a ring around a perimeter, not an area.
@@ -4118,7 +4122,7 @@ const GLGizmoTextureDisplacement::LibraryTexture *GLGizmoTextureDisplacement::ge
     if (entry.image_data) {
         TextureDisplacementLayer probe;
         probe.image_data = entry.image_data;
-        entry.thumbnail  = upload_height_thumbnail(decode_height_texture(probe));
+        entry.thumbnail  = upload_height_thumbnail(decode_height_texture(probe, /* keep_decoded */ false));
         if (!entry.thumbnail)
             entry.image_data.reset(); // decoded to nothing usable - treat it as a failed load
     } else {
@@ -4331,6 +4335,8 @@ void GLGizmoTextureDisplacement::render_texture_library_popup(const ImVec2 &pane
     std::optional<TextureLibraryEntry> to_remove;
     bool                               import_clicked = false;
     bool                               download_clicked = false;
+    int                                loads_left       = PICKER_LOADS_PER_FRAME;
+    bool                               loads_deferred   = false;
 
     // Tiles are placed on the four-column grid explicitly rather than flowed with SameLine(): a user tile
     // overlays a remove button on its corner, and that button would otherwise be "the previous item" the
@@ -4348,11 +4354,30 @@ void GLGizmoTextureDisplacement::render_texture_library_popup(const ImVec2 &pane
     };
     // One section's tiles, in the order the section holds them (shipped alphabetically, pack textures by
     // name, the user's own most recently used first - the order texture_library() produced); a user tile
-    // carries a remove button on hover. Returns how many it drew.
+    // carries a remove button on hover. Returns how many tiles it laid out, drawn or not.
     const auto grid = [&](const ImVec2 &origin, const std::vector<const TextureLibraryEntry *> &entries, bool removable) {
         int n = 0;
         for (const TextureLibraryEntry *entry : entries) {
-            ImGui::SetCursorScreenPos(tile_pos(origin, n++));
+            const ImVec2 rect_min = tile_pos(origin, n++);
+            const ImVec2 rect_max = ImVec2(rect_min.x + tile, rect_min.y + tile);
+            const bool   current  = entry->path == layer->path;
+            // The selected tile is centred even when it is off screen, so it is drawn and loaded next frame.
+            if (current && m_picker_reveal_selected) {
+                ImGui::SetScrollFromPosY(0.5f * (rect_min.y + rect_max.y) - ImGui::GetWindowPos().y, 0.5f);
+                m_parent.request_extra_frame();
+            }
+            if (!ImGui::IsRectVisible(rect_min, rect_max))
+                continue;
+            // Thumbnails decode on this thread, so only a few per frame; the rest fill in on later frames.
+            const bool cached = m_library_textures.count(entry->path) != 0;
+            if (!cached && loads_left == 0) {
+                loads_deferred = true;
+                dl->AddRectFilled(rect_min, rect_max, ImGui::GetColorU32(ImGuiCol_FrameBg), style.FrameRounding);
+                continue;
+            }
+            if (!cached)
+                --loads_left;
+            ImGui::SetCursorScreenPos(rect_min);
             ImGui::PushID(entry->path.c_str());
             const LibraryTexture *tex     = get_library_texture(entry->path);
             GLTexture            *thumb   = tex != nullptr ? tex->thumbnail.get() : nullptr;
@@ -4375,7 +4400,6 @@ void GLGizmoTextureDisplacement::render_texture_library_popup(const ImVec2 &pane
             if (removable)
                 ImGui::SetItemAllowOverlap(); // the remove button drawn over its corner takes its own clicks
             const ImVec2 a       = ImGui::GetItemRectMin(), b = ImGui::GetItemRectMax();
-            const bool   current = entry->path == layer->path;
             const bool   hovered = ImGui::IsItemHovered();
             // The layer's current texture carries an accent ring, and the tile under the pointer a thinner,
             // fainter one. Both are drawn inside the tile, where the grid's clip rect never cuts them.
@@ -4384,9 +4408,6 @@ void GLGizmoTextureDisplacement::render_texture_library_popup(const ImVec2 &pane
                 dl->AddRect(ImVec2(a.x + 0.5f * w, a.y + 0.5f * w), ImVec2(b.x - 0.5f * w, b.y - 0.5f * w),
                             ImGui::GetColorU32(current ? orca : ImVec4(orca.x, orca.y, orca.z, 0.6f)), 0.f, 0, w);
             }
-            // Centred, as far as the scroll range allows, so the textures around it are in view too.
-            if (current && m_picker_reveal_selected)
-                ImGui::SetScrollFromPosY(0.5f * (a.y + b.y) - ImGui::GetWindowPos().y, 0.5f);
             if (hovered)
                 panel_tooltip(entry->name);
 
@@ -4575,6 +4596,8 @@ void GLGizmoTextureDisplacement::render_texture_library_popup(const ImVec2 &pane
         ImGui::TextDisabled("%s", _u8L("PNG, JPG or BMP - converted to a height map on import. Hover one of yours to remove it.").c_str());
         ImGui::PopTextWrapPos();
     }
+    if (loads_deferred)
+        m_parent.request_extra_frame();
     // Done whether or not the current texture was drawn: one in a collapsed section stays where it is.
     m_picker_reveal_selected = false;
     ImGui::EndChild();

src/slic3r/GUI/TextureLibrary.cpp

@@ -223,23 +223,11 @@ std::vector<unsigned char> read_file_bytes(const std::string &path)
     return std::vector<unsigned char>(std::istreambuf_iterator<char>(ifs), std::istreambuf_iterator<char>());
 }
 
-// True if these bytes are a PNG libslic3r can decode, i.e. can be stored on a layer as-is. Mirrors
-// exactly what decode_height_texture() accepts: 8-bit grayscale, or 8-bit colour (whose luminance is
-// the height and whose RGB is available to colour the model). Anything else is converted on load.
+// True if decode_height_texture() can read these bytes, so they can be stored on a layer as-is.
+// Anything else is converted on load.
 bool is_supported_height_map(const std::vector<unsigned char> &bytes)
 {
-    if (bytes.empty())
-        return false;
-    const png::ReadBuf rbuf{ bytes.data(), bytes.size() };
-    if (!png::is_png(rbuf))
-        return false;
-    png::ImageGreyscale gray;
-    if (png::decode_png(rbuf, gray) && gray.cols > 0 && gray.rows > 0)
-        return true;
-    png::ImageColorscale color;
-    return png::decode_colored_png(rbuf, color) && color.cols > 0 && color.rows > 0 &&
-           color.bytes_per_pixel >= 3 &&
-           color.buf.size() == color.cols * color.rows * size_t(color.bytes_per_pixel);
+    return !bytes.empty() && png::is_decodable_8bit_png(png::ReadBuf{ bytes.data(), bytes.size() });
 }
 
 std::vector<TextureLibraryEntry> g_library;

src/slic3r/plugin/PluginFsUtils.cpp

@@ -34,10 +34,6 @@
 #include <unordered_set>
 #include <vector>
 
-#ifdef WIN32
-#include <boost/locale/encoding_utf.hpp>
-#endif
-
 namespace Slic3r {
 
 const char* const INSTALL_STATE_FILE = ".install_state.json";
@@ -665,7 +661,7 @@ bool extract_zip_to_directory(const boost::filesystem::path& zip_path, const boo
     namespace fs = boost::filesystem;
 
     boost::system::error_code ec;
-    fs::create_directories(destination, ec);
+    fs::create_directories(extended_path(destination), ec);
     if (ec) {
         error = "Failed to create plugin staging directory: " + ec.message();
         return false;
@@ -709,7 +705,7 @@ bool extract_zip_to_directory(const boost::filesystem::path& zip_path, const boo
 
         const fs::path output_path = destination / relative_path;
         if (stat.m_is_directory || mz_zip_reader_is_file_a_directory(&reader.archive, stat.m_file_index)) {
-            fs::create_directories(output_path, ec);
+            fs::create_directories(extended_path(output_path), ec);
             if (ec) {
                 error = "Failed to create plugin zip directory " + output_path.string() + ": " + ec.message();
                 return false;
@@ -717,26 +713,19 @@ bool extract_zip_to_directory(const boost::filesystem::path& zip_path, const boo
             continue;
         }
 
-        fs::create_directories(output_path.parent_path(), ec);
+        fs::create_directories(extended_path(output_path.parent_path()), ec);
         if (ec) {
             error = "Failed to create plugin zip parent directory " + output_path.parent_path().string() + ": " + ec.message();
             return false;
         }
 
-        if (fs::exists(output_path, ec) && fs::is_directory(output_path, ec)) {
+        if (fs::exists(extended_path(output_path), ec) && fs::is_directory(extended_path(output_path), ec)) {
             error = "Plugin zip file conflicts with an existing directory: " + output_path.string();
             return false;
         }
 
-        const std::string encoded_output_path = encode_path(output_path.string().c_str());
-        mz_bool extracted = mz_zip_reader_extract_to_file(&reader.archive, stat.m_file_index, encoded_output_path.c_str(), 0);
-#ifdef WIN32
-        if (!extracted) {
-            const std::wstring wide_output_path = boost::locale::conv::utf_to_utf<wchar_t>(output_path.generic_string());
-            extracted = mz_zip_reader_extract_to_file_w(&reader.archive, stat.m_file_index, wide_output_path.c_str(), 0);
-        }
-#endif
-        if (!extracted) {
+        // Shared with the rest of the archive code: long-path capable and binary-safe.
+        if (!extract_zip_entry_to_file(&reader.archive, stat.m_file_index, output_path)) {
             error = "Failed to extract plugin zip entry " + relative_key + ": " +
                     MZ_Archive::get_errorstr(mz_zip_get_last_error(&reader.archive));
             return false;

src/slic3r/plugin/PythonInterpreter.cpp

@@ -584,19 +584,6 @@ bool PythonInterpreter::initialize()
         }
         BOOST_LOG_TRIVIAL(debug) << "Program name set successfully";
 
-        // Keep bytecode out of the Python home. The shipped .pyc files are stale against their
-        // sources, so a writable install would rewrite them inside the app (breaking a signed
-        // macOS bundle's seal) and a read-only one would recompile them on every launch.
-        const std::string pycache_prefix = data_dir() + "/python/pycache";
-#ifdef _WIN32
-        status = PyConfig_SetString(&config, &config.pycache_prefix, boost::nowide::widen(pycache_prefix).c_str());
-#else
-        status = PyConfig_SetBytesString(&config, &config.pycache_prefix, pycache_prefix.c_str());
-#endif
-        if (PyStatus_Exception(status))
-            BOOST_LOG_TRIVIAL(warning) << "Failed to set the Python bytecode cache to " << pycache_prefix << ": "
-                                       << (status.err_msg ? status.err_msg : "unknown error");
-
         // Use pybind11's scoped_interpreter which properly initializes
         // pybind11 internals for multi-threaded use — raw Py_InitializeFromConfig
         // does not set up thread state tracking that pybind11 requires.

tests/libslic3r/test_miniz_extension.cpp

@@ -18,6 +18,7 @@
 #include <fstream>
 #include <ios>
 #include <iterator>
+#include <libslic3r/Utils.hpp>
 #include <miniz.h>
 #include <string>
 #include <utility>
@@ -176,6 +177,55 @@ TEST_CASE("Confined extraction writes nothing outside the target for Windows-spe
     CHECK(list_dir(tmp.path()) == std::vector<std::string>{"bundle.zip", "cache"});
 }
 
+TEST_CASE("Confined extraction writes files under a target path longer than MAX_PATH", "[MinizExtension]")
+{
+    ScopedTemporaryDir tmp;
+    const fs::path     zip_file = tmp.path() / "bundle.zip";
+    // Directory entries are explicit: extract_archive_confined recreates directories only for them.
+    write_zip(zip_file, {{"vendor/", ""}, {"vendor/machine/", ""}, {"vendor.json", "{\"a\":1}"},
+                         {"vendor/machine/printer.json", "{\"b\":2}"}});
+
+    // One 240-char component keeps every name below the NTFS 255 limit while pushing the full
+    // target path past the 260-char MAX_PATH the Win32 APIs enforce when LongPathsEnabled is off.
+    const fs::path target = tmp.path() / std::string(240, 'd');
+    REQUIRE(target.string().size() > 260);
+    fs::create_directories(extended_path(target));
+
+    REQUIRE(extract_archive_confined(zip_file.string(), target.string()));
+    // Verify through extended-length paths, otherwise the checks themselves are bounded by MAX_PATH.
+    CHECK(fs::is_directory(extended_path(target / "vendor")));
+    CHECK(read_file(extended_path(target / "vendor.json")) == "{\"a\":1}");
+    CHECK(read_file(extended_path(target / "vendor" / "machine" / "printer.json")) == "{\"b\":2}");
+
+    // The temporary dir guard cannot remove a deep tree on Windows, so drop it here.
+    boost::system::error_code ec;
+    fs::remove_all(extended_path(target), ec);
+    CHECK_FALSE(ec);
+}
+
+TEST_CASE("A zip archive under a path longer than MAX_PATH can be written and read", "[MinizExtension]")
+{
+    ScopedTemporaryDir tmp;
+
+    // Create the long directory with the extended-length path, then exercise the archive
+    // reader/writer against an archive whose own path is past MAX_PATH.
+    const fs::path long_dir = tmp.path() / std::string(240, 'z');
+    fs::create_directories(extended_path(long_dir));
+    const fs::path zip_file = long_dir / "bundle.zip";
+    REQUIRE(zip_file.string().size() > 260);
+
+    write_zip(zip_file, {{"vendor.json", "{\"a\":1}"}});
+
+    const fs::path target = tmp.path() / "out";
+    fs::create_directories(target);
+    REQUIRE(extract_archive_confined(zip_file.string(), target.string()));
+    CHECK(read_file(target / "vendor.json") == "{\"a\":1}");
+
+    boost::system::error_code ec;
+    fs::remove_all(extended_path(long_dir), ec);
+    CHECK_FALSE(ec);
+}
+
 #ifndef _WIN32
 TEST_CASE("Confined extraction replaces a symlink at the destination instead of writing through it", "[MinizExtension]")
 {

tests/libslic3r/test_utils.cpp

@@ -521,3 +521,49 @@ TEST_CASE("ascii_iequals compares ASCII letters regardless of case", "[Utils]")
     CHECK_FALSE(ascii_iequals("[", "{"));
     CHECK_FALSE(ascii_iequals("@", "`"));
 }
+
+TEST_CASE("extended_path turns a Windows path into its long-path form", "[Utils]") {
+#ifdef _WIN32
+    namespace fs = boost::filesystem;
+
+    SECTION("a normal absolute drive path is prefixed") {
+        CHECK(extended_path(fs::path(R"(C:\models\model.3mf)")).wstring() == LR"(\\?\C:\models\model.3mf)");
+    }
+    SECTION("separators are made native") {
+        CHECK(extended_path(fs::path("C:/models/model.3mf")).wstring() == LR"(\\?\C:\models\model.3mf)");
+    }
+    SECTION("dot segments are collapsed before prefixing") {
+        // The "\\?\" prefix disables Win32 normalisation, so "." and ".." must be gone beforehand.
+        CHECK(extended_path(fs::path(R"(C:\models\..\model.3mf)")).wstring() == LR"(\\?\C:\model.3mf)");
+    }
+    SECTION("a trailing separator is dropped, not turned into a dot element") {
+        CHECK(extended_path(fs::path(R"(C:\models\)")).wstring() == LR"(\\?\C:\models)");
+    }
+    SECTION("a UNC path becomes an extended UNC path") {
+        CHECK(extended_path(fs::path(R"(\\server\share\model.3mf)")).wstring() == LR"(\\?\UNC\server\share\model.3mf)");
+    }
+    SECTION("an already extended path is returned unchanged") {
+        const fs::path extended(R"(\\?\C:\models\model.3mf)");
+        CHECK(extended_path(extended) == extended);
+    }
+    SECTION("a device path is returned unchanged") {
+        const fs::path device(R"(\\.\C:\models\model.3mf)");
+        CHECK(extended_path(device) == device);
+    }
+    SECTION("a bare device path without a root directory is returned unchanged") {
+        // Not "absolute" by Boost's rules, so it must be recognized before absolutizing.
+        const fs::path device(R"(\\.\PhysicalDrive0)");
+        CHECK(extended_path(device) == device);
+    }
+    SECTION("a relative path is completed against the working directory") {
+        const fs::path result = extended_path(fs::path("model.3mf"));
+        CHECK(result.wstring().rfind(L"\\\\?\\", 0) == 0);
+        CHECK(result.filename() == fs::path("model.3mf"));
+    }
+#else
+    SECTION("non-Windows returns the path unchanged") {
+        const boost::filesystem::path p = boost::filesystem::temp_directory_path() / "model.3mf";
+        CHECK(extended_path(p) == p);
+    }
+#endif
+}

tests/slic3rutils/test_plugin_install.cpp

@@ -3,6 +3,7 @@
 #include <catch2/catch_all.hpp>
 
 #include <ios>
+#include <libslic3r/Utils.hpp>
 #include <slic3r/plugin/PluginLoader.hpp>
 #include <slic3r/plugin/PluginDescriptor.hpp>
 #include <slic3r/plugin/PluginFsUtils.hpp>
@@ -10,13 +11,17 @@
 #include <catch2/catch_test_macros.hpp>
 #include <catch2/matchers/catch_matchers.hpp>
 #include <catch2/matchers/catch_matchers_string.hpp>
+#include "catch2/catch_message.hpp"
 #include "plugin_test_utils.hpp"
+#include "test_utils.hpp"
 
 #include <boost/filesystem.hpp>
 
 #include <fstream>
 #include <string>
 
+#include <libslic3r/Zipper.hpp>
+
 using namespace Slic3r;
 namespace fs = boost::filesystem;
 
@@ -31,6 +36,14 @@ fs::path write_py_file(const fs::path& dir, const std::string& filename, const s
     return p;
 }
 
+// The shared production helper: makes the path absolute and lexically normalized and, on
+// Windows, prefixes it with the extended-length "\\?\" form, so the test can create, verify and
+// clean up a tree past MAX_PATH even with LongPathsEnabled off. Identity on other platforms.
+fs::path to_extended_path(const fs::path& p)
+{
+    return Slic3r::extended_path(p);
+}
+
 } // namespace
 
 TEST_CASE("install_plugin rejects a cloud UUID containing path traversal", "[PluginInstall]")
@@ -184,3 +197,59 @@ TEST_CASE("an unsubscribed cloud plugin follows its header version", "[PluginIns
     REQUIRE(read_install_state(plugin_dir, scanned));
     CHECK(scanned.installed_version == "1.0.0");
 }
+
+TEST_CASE("extract_zip_to_directory writes entries under a destination longer than MAX_PATH",
+          "[PluginInstall][PluginFsUtils]")
+{
+    ScopedTemporaryDir dir("deep-extract");
+
+    const fs::path wheel = dir.path() / "deep_pkg-1.0-py3-none-any.whl";
+    const std::string payload = "print('hello from a deep path')\n";
+    {
+        Zipper zipper(wheel.string(), Zipper::NO_COMPRESSION);
+        zipper.add_entry("pkg/", "", 0); // explicit directory entry
+        zipper.add_entry("pkg/module.py", payload.data(), payload.size());
+        zipper.finalize();
+    }
+
+    // A single 240-char component keeps every filename below the NTFS 255 limit while pushing the
+    // full destination (temp dir + component) past the 260-char MAX_PATH the Win32 APIs enforce
+    // when LongPathsEnabled is off.
+    const fs::path destination = dir.path() / std::string(240, 'd');
+    REQUIRE(destination.string().size() > 260);
+
+    std::string error;
+    REQUIRE(extract_zip_to_directory(wheel, destination, error));
+    INFO("extract error: " << error);
+    CHECK(error.empty());
+
+    // Verify through a long-path-capable path, otherwise the check itself is bounded by MAX_PATH.
+    const fs::path module_py = destination / "pkg" / "module.py";
+    REQUIRE(fs::exists(to_extended_path(module_py)));
+    REQUIRE(fs::is_regular_file(to_extended_path(module_py)));
+
+    // Remove the deep subtree here: ScopedTemporaryDir's plain remove_all cannot reach past
+    // MAX_PATH on Windows.
+    boost::system::error_code ec;
+    fs::remove_all(to_extended_path(destination), ec);
+    CHECK_FALSE(ec);
+}
+
+TEST_CASE("extract_zip_to_directory rejects an entry that escapes the destination",
+          "[PluginInstall][PluginFsUtils]")
+{
+    ScopedTemporaryDir dir("escape-extract");
+
+    const fs::path wheel = dir.path() / "evil-1.0-py3-none-any.whl";
+    {
+        Zipper zipper(wheel.string(), Zipper::NO_COMPRESSION);
+        zipper.add_entry("pkg/module.py", "print('ok')\n", 12);
+        zipper.add_entry("../escape.txt", "escaped\n", 8);
+        zipper.finalize();
+    }
+
+    std::string error;
+    CHECK_FALSE(extract_zip_to_directory(wheel, dir.path() / "out", error));
+    CHECK_THAT(error, Catch::Matchers::ContainsSubstring("escapes the plugin package"));
+    CHECK_FALSE(fs::exists(dir.path() / "escape.txt"));
+}

tests/slic3rutils/test_plugin_lifecycle.cpp

@@ -615,22 +615,8 @@ TEST_CASE("Python module release removes package submodules and owned sys.path",
 
     // Ensure the next import executes the new submodule rather than reusing a stale package child.
     write_package("'new'");
-    {
-        // The rewrite can keep the old mtime and size, so drop the bytecode wherever the
-        // interpreter caches it.
-        PythonGILState gil;
-        REQUIRE(gil);
-        PyObjectPtr util(PyImport_ImportModule("importlib.util"));
-        REQUIRE(util);
-        for (const char* file : {"__init__.py", "sub.py"}) {
-            PyObjectPtr source(PyUnicode_DecodeFSDefault((package_root / file).string().c_str()));
-            REQUIRE(source);
-            PyObjectPtr cached(PyObject_CallMethod(util.get(), "cache_from_source", "O", source.get()));
-            REQUIRE(cached);
-            boost::system::error_code ec;
-            fs::remove(fs::path(PyUnicode_AsUTF8(cached.get())), ec);
-        }
-    }
+    boost::system::error_code ec;
+    fs::remove_all(package_root / "__pycache__", ec);
 
     paths.clear();
     modules.clear();