Hide unicode directional control characters

They shouldn't be looked up in the font and displayed under any
circumstances.

desktop_version/src/Font.cpp

@@ -1074,6 +1074,12 @@ static int print_char(
 {
     /* Draws the glyph for a codepoint at x,y.
      * Returns the amount of pixels to advance the cursor. */
+    if (is_directional_character(codepoint) || is_joiner(codepoint))
+    {
+        // Some characters should be completely invisible
+        return 0;
+    }
+
     const Font* f_glyph;
     GlyphInfo* glyph = find_glyphinfo(f, codepoint, &f_glyph);
     if (glyph == NULL)

desktop_version/src/FontBidi.cpp

@@ -263,6 +263,25 @@ void bidi_destroy(void)
 }
 
 
+bool is_directional_character(const uint32_t codepoint)
+{
+    // LEFT-TO-RIGHT MARK and RIGHT-TO-LEFT MARK
+    if (codepoint == 0x200E || codepoint == 0x200F) return true;
+
+    // Some other directional formatting: LRE, RLE, PDF, RLO, LRO
+    if (codepoint >= 0x202A && codepoint <= 0x202E) return true;
+
+    // The more recent isolates: LRI, RLI, FSI, PDI
+    if (codepoint >= 0x2066 && codepoint <= 0x2069) return true;
+
+    return false;
+}
+
+bool is_joiner(const uint32_t codepoint)
+{
+    return codepoint == 0x200C || codepoint == 0x200D;
+}
+
 bool bidi_should_transform(const char* text)
 {
     /* Just as an optimization, only run the whole bidi machinery if the
@@ -278,14 +297,8 @@ bool bidi_should_transform(const char* text)
         // Extended Arabic B and A
         if (ch >= 0x870 && ch <= 0x8FF) return true;
 
-        // LEFT-TO-RIGHT MARK and RIGHT-TO-LEFT MARK
-        if (ch == 0x200E || ch == 0x200F) return true;
-
-        // Some other directional formatting: LRE, RLE, PDF, RLO, LRO
-        if (ch >= 0x202A && ch <= 0x202E) return true;
-
-        // The more recent isolates: LRI, RLI, FSI, PDI
-        if (ch >= 0x2066 && ch <= 0x2069) return true;
+        // Any directional control character
+        if (is_directional_character(ch)) return true;
 
         // Hebrew presentation forms
         if (ch >= 0xFB1D && ch <= 0xFB4F) return true;

desktop_version/src/FontBidi.h

@@ -1,11 +1,15 @@
 #ifndef FONTBIDI_H
 #define FONTBIDI_H
 
+#include <stdint.h>
+
 namespace font
 {
 
 void bidi_init(void);
 void bidi_destroy(void);
+bool is_directional_character(uint32_t codepoint);
+bool is_joiner(uint32_t codepoint);
 bool bidi_should_transform(const char* text);
 const char* bidi_transform(const char* text);