Fix font sub-pixel AA impacting character spacing when AA is disabled

source/blender/blenfont/BLF_api.h

@@ -375,7 +375,11 @@ enum {
   BLF_BAD_FONT = 1 << 16,
   /** This font is managed by the FreeType cache subsystem. */
   BLF_CACHED = 1 << 17,
-  /** At small sizes glyphs are rendered at multiple sub-pixel positions. */
+  /**
+   * At small sizes glyphs are rendered at multiple sub-pixel positions.
+   *
+   * \note Can be checked without checking #BLF_MONOSPACED which can be assumed to be disabled.
+   */
   BLF_RENDER_SUBPIXELAA = 1 << 18,
 };
 

source/blender/blenfont/intern/blf_glyph.cc

@@ -1322,7 +1322,7 @@ GlyphBLF *blf_glyph_ensure(FontBLF *font, GlyphCacheBLF *gc, const uint charcode
 #ifdef BLF_SUBPIXEL_AA
 GlyphBLF *blf_glyph_ensure_subpixel(FontBLF *font, GlyphCacheBLF *gc, GlyphBLF *g, int32_t pen_x)
 {
-  if (!(font->flags & BLF_RENDER_SUBPIXELAA) || (font->flags & BLF_MONOCHROME)) {
+  if (!(font->flags & BLF_RENDER_SUBPIXELAA)) {
     /* Not if we are in mono mode (aliased) or the feature is turned off. */
     return g;
   }

source/blender/editors/interface/interface_style.cc

@@ -460,8 +460,10 @@ void uiStyleInit()
     if (U.text_render & USER_TEXT_DISABLE_AA) {
       flag_enable |= BLF_MONOCHROME;
     }
-    if (U.text_render & USER_TEXT_RENDER_SUBPIXELAA) {
-      flag_enable |= BLF_RENDER_SUBPIXELAA;
+    else {
+      if (U.text_render & USER_TEXT_RENDER_SUBPIXELAA) {
+        flag_enable |= BLF_RENDER_SUBPIXELAA;
+      }
     }
 
     LISTBASE_FOREACH (uiFont *, font, &U.uifonts) {