source/blender/blenkernel/BKE_icons.h

@@ -20,6 +20,7 @@ extern "C" {
 #endif
 
 #include "BLI_compiler_attrs.h"
+#include "BLI_sys_types.h"
 
 #include "DNA_ID_enums.h"
 
@@ -110,6 +111,9 @@ struct ImBuf *BKE_icon_imbuf_get_buffer(int icon_id) ATTR_WARN_UNUSED_RESULT;
  */
 struct Icon *BKE_icon_get(int icon_id);
 
+bool BKE_icon_is_preview(int icon_id);
+bool BKE_icon_is_image(int icon_id);
+
 /**
  * Set icon for id if not already defined.
  * Used for inserting the internal icons.

source/blender/blenkernel/intern/icons.cc

@@ -860,6 +860,18 @@ Icon *BKE_icon_get(const int icon_id)
   return icon;
 }
 
+bool BKE_icon_is_preview(const int icon_id)
+{
+  const Icon *icon = BKE_icon_get(icon_id);
+  return icon->obj_type == ICON_DATA_PREVIEW;
+}
+
+bool BKE_icon_is_image(const int icon_id)
+{
+  const Icon *icon = BKE_icon_get(icon_id);
+  return icon->obj_type == ICON_DATA_IMBUF;
+}
+
 void BKE_icon_set(const int icon_id, Icon *icon)
 {
   void **val_p;

source/blender/editors/asset/ED_asset_handle.h

@@ -37,6 +37,7 @@ struct AssetHandle;
 AssetRepresentationHandle *ED_asset_handle_get_representation(const struct AssetHandle *asset);
 ID_Type ED_asset_handle_get_id_type(const struct AssetHandle *asset);
 int ED_asset_handle_get_preview_icon_id(const struct AssetHandle *asset);
+int ED_asset_handle_get_preview_or_type_icon_id(const struct AssetHandle *asset);
 void ED_asset_handle_get_full_library_path(
     const struct AssetHandle *asset,
     /* `1024` for #FILE_MAX,

source/blender/editors/asset/ED_asset_list.h

@@ -66,6 +66,8 @@ blender::asset_system::AssetRepresentation *ED_assetlist_asset_get_by_index(
     const AssetLibraryReference &library_reference, int asset_index);
 #endif
 
+bool ED_assetlist_asset_image_is_loading(const AssetLibraryReference *library_reference,
+                                         const AssetHandle *asset_handle);
 struct ImBuf *ED_assetlist_asset_image_get(const AssetHandle *asset_handle);
 
 /**

source/blender/editors/asset/intern/asset_handle.cc

@@ -18,6 +18,8 @@
 
 #include "DNA_space_types.h"
 
+#include "ED_fileselect.h"
+
 #include "RNA_prototypes.h"
 
 #include "ED_asset_handle.h"
@@ -38,6 +40,11 @@ int ED_asset_handle_get_preview_icon_id(const AssetHandle *asset)
   return asset->file_data->preview_icon_id;
 }
 
+int ED_asset_handle_get_preview_or_type_icon_id(const AssetHandle *asset)
+{
+  return ED_file_icon(asset->file_data);
+}
+
 void ED_asset_handle_get_full_library_path(const AssetHandle *asset_handle,
                                            char r_full_lib_path[FILE_MAX])
 {

source/blender/editors/asset/intern/asset_list.cc

@@ -122,6 +122,7 @@ class AssetList : NonCopyable {
 
   bool needsRefetch() const;
   bool isLoaded() const;
+  bool isAssetPreviewLoading(const AssetHandle &asset) const;
   asset_system::AssetLibrary *asset_library() const;
   void iterate(AssetListHandleIterFn fn) const;
   void iterate(AssetListIterFn fn) const;
@@ -194,6 +195,11 @@ bool AssetList::isLoaded() const
   return filelist_is_ready(filelist_);
 }
 
+bool AssetList::isAssetPreviewLoading(const AssetHandle &asset) const
+{
+  return filelist_file_is_preview_pending(filelist_, asset.file_data);
+}
+
 asset_system::AssetLibrary *AssetList::asset_library() const
 {
   return reinterpret_cast<asset_system::AssetLibrary *>(filelist_asset_library(filelist_));
@@ -533,6 +539,13 @@ asset_system::AssetRepresentation *ED_assetlist_asset_get_by_index(
   return reinterpret_cast<asset_system::AssetRepresentation *>(asset_handle.file_data->asset);
 }
 
+bool ED_assetlist_asset_image_is_loading(const AssetLibraryReference *library_reference,
+                                         const AssetHandle *asset_handle)
+{
+  const AssetList *list = AssetListStorage::lookup_list(*library_reference);
+  return list->isAssetPreviewLoading(*asset_handle);
+}
+
 ImBuf *ED_assetlist_asset_image_get(const AssetHandle *asset_handle)
 {
   ImBuf *imbuf = filelist_file_getimage(asset_handle->file_data);

source/blender/editors/asset/intern/asset_shelf_asset_view.cc

@@ -118,7 +118,12 @@ void AssetView::build_items()
     const bool show_names = (shelf_.settings.display_flag & ASSETSHELF_SHOW_NAMES);
 
     const StringRef identifier = asset->get_identifier().library_relative_identifier();
-    const int preview_id = ED_asset_handle_get_preview_icon_id(&asset_handle);
+    const int preview_id = [this, &asset_handle]() -> int {
+      if (ED_assetlist_asset_image_is_loading(&library_ref_, &asset_handle)) {
+        return ICON_TEMP;
+      }
+      return ED_asset_handle_get_preview_or_type_icon_id(&asset_handle);
+    }();
 
     AssetViewItem &item = add_item<AssetViewItem>(
         asset_handle, identifier, asset->get_name(), preview_id);

source/blender/editors/interface/interface_intern.hh

@@ -1191,13 +1191,18 @@ void ui_draw_preview_item(const uiFontStyle *fstyle,
 /**
  * Version of #ui_draw_preview_item() that does not draw the menu background and item text based on
  * state. It just draws the preview and text directly.
+ *
+ * \param draw_as_icon: Instead of stretching the preview/icon to the available width/height, draw
+ *                      it at the standard icon size. Mono-icons will draw with \a text_col or the
+ *                      corresponding theme override for this type of icon.
  */
 void ui_draw_preview_item_stateless(const uiFontStyle *fstyle,
                                     rcti *rect,
                                     const char *name,
                                     int iconid,
                                     const uchar text_col[4],
-                                    eFontStyle_Align text_align);
+                                    eFontStyle_Align text_align,
+                                    bool draw_as_icon = false);
 
 #define UI_TEXT_MARGIN_X 0.4f
 #define UI_POPUP_MARGIN (UI_SCALE_FAC * 12)

source/blender/editors/interface/interface_widgets.cc

@@ -1344,6 +1344,32 @@ static void widget_draw_preview(BIFIconID icon, float alpha, const rcti *rect)
   }
 }
 
+static void widget_draw_icon_centered(const BIFIconID icon,
+                                      const float aspect,
+                                      const float alpha,
+                                      const rcti *rect,
+                                      const uchar mono_color[4])
+{
+  if (icon == ICON_NONE) {
+    return;
+  }
+
+  const float size = ICON_DEFAULT_HEIGHT / (aspect * UI_INV_SCALE_FAC);
+
+  if (size > 0) {
+    const int x = BLI_rcti_cent_x(rect) - size / 2;
+    const int y = BLI_rcti_cent_y(rect) - size / 2;
+
+    const bTheme *btheme = UI_GetTheme();
+    const float desaturate = 1.0 - btheme->tui.icon_saturation;
+    uchar color[4] = {mono_color[0], mono_color[1], mono_color[2], mono_color[3]};
+    const bool has_theme = UI_icon_get_theme_color(int(icon), color);
+
+    UI_icon_draw_ex(
+        x, y, icon, aspect * UI_INV_SCALE_FAC, alpha, desaturate, color, has_theme, nullptr);
+  }
+}
+
 static int ui_but_draw_menu_icon(const uiBut *but)
 {
   return (but->flag & UI_BUT_ICON_SUBMENU) && (but->emboss == UI_EMBOSS_PULLDOWN);
@@ -4202,8 +4228,17 @@ static void widget_preview_tile(uiBut *but,
     widget_list_itembut(wcol, rect, state, roundboxalign, zoom);
   }
 
-  ui_draw_preview_item_stateless(
-      &UI_style_get()->widget, rect, but->drawstr, but->icon, wcol->text, UI_STYLE_TEXT_CENTER);
+  /* When the button is not tagged as having a preview icon, do regular icon drawing with the
+   * standard icon size. */
+  const bool draw_as_icon = !(but->flag & UI_BUT_ICON_PREVIEW);
+
+  ui_draw_preview_item_stateless(&UI_style_get()->widget,
+                                 rect,
+                                 but->drawstr,
+                                 but->icon,
+                                 wcol->text,
+                                 UI_STYLE_TEXT_CENTER,
+                                 draw_as_icon);
 }
 
 static void widget_optionbut(uiWidgetColors *wcol,
@@ -5570,18 +5605,36 @@ void ui_draw_preview_item_stateless(const uiFontStyle *fstyle,
                                     const char *name,
                                     int iconid,
                                     const uchar text_col[4],
-                                    eFontStyle_Align text_align)
+                                    eFontStyle_Align text_align,
+                                    bool draw_as_icon)
 {
   rcti trect = *rect;
   const float text_size = UI_UNIT_Y;
   const bool has_text = name && name[0];
 
+  float alpha = 1.0f;
+
+  {
+    /* Special handling: Previews often want to show a loading icon while the preview is being
+     * loaded. Draw this with reduced opacity. */
+    const bool is_loading_icon = iconid == ICON_TEMP;
+    if (is_loading_icon) {
+      alpha *= 0.5f;
+      draw_as_icon = true;
+    }
+  }
+
   if (has_text) {
     /* draw icon in rect above the space reserved for the label */
     rect->ymin += text_size;
   }
   GPU_blend(GPU_BLEND_ALPHA);
-  widget_draw_preview(BIFIconID(iconid), 1.0f, rect);
+  if (draw_as_icon) {
+    widget_draw_icon_centered(BIFIconID(iconid), 1.0f, alpha, rect, text_col);
+  }
+  else {
+    widget_draw_preview(BIFIconID(iconid), alpha, rect);
+  }
   GPU_blend(GPU_BLEND_NONE);
 
   if (!has_text) {

source/blender/editors/interface/views/grid_view.cc

@@ -9,6 +9,8 @@
 #include <limits>
 #include <stdexcept>
 
+#include "BKE_icons.h"
+
 #include "BLI_index_range.hh"
 
 #include "WM_types.h"
@@ -424,10 +426,16 @@ void PreviewGridItem::build_grid_tile(uiLayout &layout) const
                         0,
                         0,
                         "");
+  /* Draw icons that are not previews or images as normal icons with a fixed icon size. Otherwise
+   * they will be upscaled to the button size. Should probably be done by the widget code. */
+  const int is_preview_flag = (BKE_icon_is_preview(preview_icon_id) ||
+                               BKE_icon_is_image(preview_icon_id)) ?
+                                  UI_BUT_ICON_PREVIEW :
+                                  0;
   ui_def_but_icon(but,
                   preview_icon_id,
                   /* NOLINTNEXTLINE: bugprone-suspicious-enum-usage */
-                  UI_HAS_ICON | UI_BUT_ICON_PREVIEW);
+                  UI_HAS_ICON | is_preview_flag);
   UI_but_func_tooltip_label_set(but, [this](const uiBut * /*but*/) { return label; });
   but->emboss = UI_EMBOSS_NONE;
 }

source/blender/editors/space_file/file_draw.cc

@@ -361,7 +361,7 @@ static void file_draw_preview(const FileList *files,
   bool show_outline = !is_icon && (file->typeflag & (FILE_TYPE_IMAGE | FILE_TYPE_OBJECT_IO |
                                                      FILE_TYPE_MOVIE | FILE_TYPE_BLENDER));
   const bool is_offline = (file->attributes & FILE_ATTR_OFFLINE);
-  const bool is_loading = !filelist_is_ready(files) || file->flags & FILE_ENTRY_PREVIEW_LOADING;
+  const bool is_loading = filelist_file_is_preview_pending(files, file);
 
   BLI_assert(imb != nullptr);
 

source/blender/editors/space_file/filelist.cc

@@ -1160,6 +1160,14 @@ void filelist_file_get_full_path(const FileList *filelist,
   BLI_path_join(r_filepath, FILE_MAX_LIBEXTRA, root, file->relpath);
 }
 
+bool filelist_file_is_preview_pending(const FileList *filelist, const FileDirEntry *file)
+{
+  /* Actual preview loading is only started after the filelist is loaded, so the file isn't flagged
+   * with #FILE_ENTRY_PREVIEW_LOADING yet. */
+  const bool filelist_ready = filelist_is_ready(filelist);
+  return !filelist_ready || file->flags & FILE_ENTRY_PREVIEW_LOADING;
+}
+
 static FileDirEntry *filelist_geticon_get_file(FileList *filelist, const int index)
 {
   BLI_assert(G.background == false);

source/blender/editors/space_file/filelist.hh

@@ -74,6 +74,7 @@ void filelist_free_icons(void);
 void filelist_file_get_full_path(const FileList *filelist,
                                  const FileDirEntry *file,
                                  char r_filepath[/*FILE_MAX_LIBEXTRA*/]);
+bool filelist_file_is_preview_pending(const FileList *filelist, const FileDirEntry *file);
 ImBuf *filelist_getimage(FileList *filelist, int index);
 ImBuf *filelist_file_getimage(const FileDirEntry *file);
 ImBuf *filelist_geticon_image_ex(const FileDirEntry *file);