Don't rescale powerline or nerd fonts

Part of xtermjs#4969

src/browser/renderer/shared/RendererUtils.ts

@@ -23,23 +23,40 @@ export function isRestrictedPowerlineGlyph(codepoint: number): boolean {
   return 0xE0B0 <= codepoint && codepoint <= 0xE0B7;
 }
 
+function isNerdFontGlyph(codepoint: number): boolean {
+  return 0xE000 <= codepoint && codepoint <= 0xF8FF;
+}
+
 function isBoxOrBlockGlyph(codepoint: number): boolean {
   return 0x2500 <= codepoint && codepoint <= 0x259F;
 }
 
 export function isEmoji(codepoint: number): boolean {
   return (
     codepoint >= 0x1F600 && codepoint <= 0x1F64F || // Emoticons
-    codepoint >= 0x1F300 && codepoint <= 0x1F5FF ||  // Misc Symbols and Pictographs
-    codepoint >= 0x1F680 && codepoint <= 0x1F6FF ||  // Transport and Map
-    codepoint >= 0x2600 && codepoint <= 0x26FF ||    // Misc symbols
-    codepoint >= 0x2700 && codepoint <= 0x27BF ||    // Dingbats
-    codepoint >= 0xFE00 && codepoint <= 0xFE0F ||    // Variation Selectors
-    codepoint >= 0x1F900 && codepoint <= 0x1F9FF ||  // Supplemental Symbols and Pictographs
+    codepoint >= 0x1F300 && codepoint <= 0x1F5FF || // Misc Symbols and Pictographs
+    codepoint >= 0x1F680 && codepoint <= 0x1F6FF || // Transport and Map
+    codepoint >= 0x2600  && codepoint <= 0x26FF  || // Misc symbols
+    codepoint >= 0x2700  && codepoint <= 0x27BF  || // Dingbats
+    codepoint >= 0xFE00  && codepoint <= 0xFE0F  || // Variation Selectors
+    codepoint >= 0x1F900 && codepoint <= 0x1F9FF || // Supplemental Symbols and Pictographs
     codepoint >= 0x1F1E6 && codepoint <= 0x1F1FF
   );
 }
 
+export function allowRescaling(codepoint: number | undefined, width: number, glyphSizeX: number, deviceCellWidth: number): boolean {
+  return (
+    // Is single cell width
+    width === 1 &&
+    // Glyph exceeds cell bounds, + 1 to avoid hurting readability
+    glyphSizeX > deviceCellWidth + 1 &&
+    // Never rescale emoji
+    codepoint !== undefined && !isEmoji(codepoint) &&
+    // Never rescale powerline or nerd fonts
+    !isPowerlineGlyph(codepoint) && !isNerdFontGlyph(codepoint)
+  );
+}
+
 export function treatGlyphAsBackgroundColor(codepoint: number): boolean {
   return isPowerlineGlyph(codepoint) || isBoxOrBlockGlyph(codepoint);
 }