Abstract away semantics of char 0 as right half of double-wide char

src/Screen.cpp

@@ -1012,7 +1012,7 @@ void Screen::displayCharacter(uint c)
         }
 
         Character &ch = _screenLines[_cuY][_cuX + i];
-        ch.character = 0;
+        ch.setRightHalfOfDoubleWide();
         ch.foregroundColor = _effectiveForeground;
         ch.backgroundColor = _effectiveBackground;
         ch.rendition = _effectiveRendition;

src/characters/Character.h

@@ -227,6 +227,16 @@ public:
     {
         return hasSameColors(lhs) && hasSameRendition(lhs) && hasSameLineDrawStatus(lhs) && isSameScript(lhs);
     }
+
+    inline bool isRightHalfOfDoubleWide() const
+    {
+        return character == 0;
+    }
+
+    inline void setRightHalfOfDoubleWide()
+    {
+        character = 0;
+    }
 };
 
 constexpr bool operator==(const Character &a, const Character &b)

src/terminalDisplay/TerminalDisplay.cpp

@@ -580,11 +580,11 @@ void TerminalDisplay::updateImage()
                 // We also take the next one into account to handle the situation
                 // where characters exceed their cell width.
                 if (dirtyMask[x] != 0) {
-                    if (newLine[x + 0].character == 0u) {
+                    if (newLine[x + 0].isRightHalfOfDoubleWide()) {
                         continue;
                     }
                     const bool lineDraw = LineBlockCharacters::canDraw(newLine[x + 0].character);
-                    const bool doubleWidth = (x + 1 == columnsToUpdate) ? false : (newLine[x + 1].character == 0);
+                    const bool doubleWidth = (x + 1 == columnsToUpdate) ? false : newLine[x + 1].isRightHalfOfDoubleWide();
                     const RenditionFlags cr = newLine[x].rendition;
                     const CharacterColor clipboard = newLine[x].backgroundColor;
                     if (newLine[x].foregroundColor != cf) {
@@ -594,11 +594,11 @@ void TerminalDisplay::updateImage()
                     for (len = 1; len < lln; ++len) {
                         const Character &ch = newLine[x + len];
 
-                        if (ch.character == 0u) {
+                        if (ch.isRightHalfOfDoubleWide()) {
                             continue; // Skip trailing part of multi-col chars.
                         }
 
-                        const bool nextIsDoubleWidth = (x + len + 1 == columnsToUpdate) ? false : (newLine[x + len + 1].character == 0);
+                        const bool nextIsDoubleWidth = (x + len + 1 == columnsToUpdate) ? false : newLine[x + len + 1].isRightHalfOfDoubleWide();
 
                         if (ch.foregroundColor != cf || ch.backgroundColor != clipboard || (ch.rendition & ~RE_EXTENDED_CHAR) != (cr & ~RE_EXTENDED_CHAR)
                             || (dirtyMask[x + len] == 0) || LineBlockCharacters::canDraw(ch.character) != lineDraw || nextIsDoubleWidth != doubleWidth) {

src/terminalDisplay/TerminalPainter.cpp

@@ -79,7 +79,7 @@ void TerminalPainter::drawContents(Character *image,
         bool doubleHeightLinePair = false;
 
         // Search for start of multi-column character
-        if ((image[display->loc(rect.x(), y)].character == 0u) && (x != 0)) {
+        if (image[display->loc(rect.x(), y)].isRightHalfOfDoubleWide() && (x != 0)) {
             x--;
         }
 
@@ -100,14 +100,13 @@ void TerminalPainter::drawContents(Character *image,
                     }
                 }
             } else {
-                const uint c = char_value.character;
-                if (c != 0u) {
-                    univec << c;
+                if (!char_value.isRightHalfOfDoubleWide()) {
+                    univec << char_value.character;
                 }
             }
 
             // TODO: Move all those lambdas to Character, so it's easy to test.
-            const bool doubleWidth = (image[qMin(pos + 1, imageSize - 1)].character == 0);
+            const bool doubleWidth = image[qMin(pos + 1, imageSize - 1)].isRightHalfOfDoubleWide();
 
             const auto isInsideDrawArea = [rectRight = rect.right()](int column) {
                 return column <= rectRight;
@@ -115,7 +114,7 @@ void TerminalPainter::drawContents(Character *image,
 
             const auto hasSameWidth = [imageSize, image, doubleWidth](int nextPos) {
                 const int characterLoc = qMin(nextPos + 1, imageSize - 1);
-                return (image[characterLoc].character == 0) == doubleWidth;
+                return image[characterLoc].isRightHalfOfDoubleWide() == doubleWidth;
             };
 
             if (char_value.canBeGrouped(bidiEnabled, doubleWidth)) {
@@ -166,7 +165,7 @@ void TerminalPainter::drawContents(Character *image,
             }
 
             // Adjust for trailing part of multi-column character
-            if ((x + len < display->usedColumns()) && (image[display->loc(x + len, y)].character == 0u)) {
+            if ((x + len < display->usedColumns()) && image[display->loc(x + len, y)].isRightHalfOfDoubleWide()) {
                 len++;
             }