feat: add optional improved text wrapping (Chatterino#6265)

See the cmake flag `CHATTERINO_ALLOW_PRIVATE_QT_API` for details on how to test this.

Author: Nerixyz

.clang-tidy

@@ -19,6 +19,7 @@ Checks: "-*,
   -cppcoreguidelines-owning-memory,
   -cppcoreguidelines-avoid-magic-numbers,
   -cppcoreguidelines-avoid-const-or-ref-data-members,
+  -cppcoreguidelines-avoid-do-while,
   -readability-magic-numbers,
   -performance-noexcept-move-constructor,
   -misc-non-private-member-variables-in-classes,

CHANGELOG.md

@@ -82,6 +82,7 @@
 - Dev: Emoji style / set is now stored lowercase (and matched case-insensitively). Changing emoji style from this point on and then running an old version might mean you will use the Twitter emoji style by default. (#6300)
 - Dev: Refactored `OnceFlag`. (#6237, #6316)
 - Dev: Bumped clang-format requirement to 19. (#6236)
+- Dev: Added optional improved text wrapping through private Qt APIs. (#6265)
 - Dev: Factored out AUMID to `Version`. (#6321)
 - Dev: Silenced some warnings when compiling with clang-cl. (#6331)
 - Dev: Added some commands for forcing a relayout (and related things) in channel views. (#6342)

CMakeLists.txt

@@ -30,6 +30,7 @@ option(BUILD_SHARED_LIBS "" OFF)
 option(CHATTERINO_LTO "Enable LTO for all targets" OFF)
 option(CHATTERINO_PLUGINS "Enable ALPHA plugin support in Chatterino" ON)
 option(CHATTERINO_USE_GDI_FONTENGINE "Use the legacy GDI fontengine instead of the new DirectWrite one on Windows (Qt 6.8.0 and later)" ON)
+option(CHATTERINO_ALLOW_PRIVATE_QT_API "Allow uses of Qt's private API - when enabling this, Chatterino must use the EXACT Qt version it was compiled against" OFF)
 
 option(CHATTERINO_UPDATER "Enable update checks" ON)
 mark_as_advanced(CHATTERINO_UPDATER)

src/CMakeLists.txt

@@ -874,6 +874,12 @@ if (CHATTERINO_PLUGINS)
     target_link_libraries(${LIBRARY_PROJECT} PUBLIC lua sol2::sol2)
 endif()
 
+if (CHATTERINO_ALLOW_PRIVATE_QT_API)
+    target_link_libraries(${LIBRARY_PROJECT} PUBLIC Qt${MAJOR_QT_VERSION}::GuiPrivate)
+    target_compile_definitions(${LIBRARY_PROJECT} PUBLIC 
+        CHATTERINO_WITH_PRIVATE_QT_API)
+endif()
+
 if (BUILD_WITH_QTKEYCHAIN)
     target_link_libraries(${LIBRARY_PROJECT}
             PUBLIC

src/messages/MessageElement.cpp

@@ -20,6 +20,10 @@
 #include <QJsonObject>
 #include <QJsonValue>
 
+#ifdef CHATTERINO_WITH_PRIVATE_QT_API
+#    include <QtGui/private/qtextengine_p.h>
+#endif
+
 namespace chatterino {
 
 using namespace literals;
@@ -621,13 +625,93 @@ void TextElement::addToContainer(MessageLayoutContainer &container,
                 }
             }
 
-            // we done goofed, we need to wrap the text
+            // We done goofed, we need to wrap the text.
+            // If we allow the use of private Qt APIs, we can use Qt's text
+            // engine to accurately calculate the width of the text. Otherwise,
+            // we have to fall back to using horizontalAdvance which has some
+            // corner cases when processing whole words (see #5944).
+#ifdef CHATTERINO_WITH_PRIVATE_QT_API
+            auto font =
+                app->getFonts()->getFont(this->style_, container.getScale());
+
+            // This code is similar to the one from QTextEngine::elidedText in
+            // the mode Qt::ElideRight (because that's essentially what we're
+            // doing here): https://github.com/qt/qtbase/blob/560bf5a07720eaa8cc589f424743db8ed1f1d902/src/gui/text/qtextengine.cpp#L3145
+            // A difference is that, once we detected EOL, we start again.
+
+            // The start of the current line in `word`
+            qsizetype actualStart = 0;
+            // This is treated like a view (from `actualStart`) over the word.
+            // It's a QString because QStackTextEngine doesn't support
+            // QStringViews as arguments.
+            QString view = word;
+
+            // This is essentially a loop over every line of text.
+            do
+            {
+                QStackTextEngine engine(view, font);
+                engine.validate();  // initialize the internal state
+
+                int pos = 0;
+                int nextBreak = 0;
+                QFixed currentWidth = 0;
+                int to = static_cast<int>(view.size());
+                bool needsBreak = false;
+
+                // Find the next grapheme boundary (`nextBreak`) at which we
+                // need to break because the text wouldn't fit into the
+                // container anymore.
+                do
+                {
+                    pos = nextBreak;
+
+                    ++nextBreak;
+                    while (nextBreak < engine.layoutData->string.size() &&
+                           !engine.attributes()[nextBreak].graphemeBoundary)
+                    {
+                        ++nextBreak;
+                    }
+
+                    auto nextWidth =
+                        currentWidth + engine.width(pos, nextBreak - pos);
+                    if (!container.fitsInLine(nextWidth.toReal()))
+                    {
+                        needsBreak = true;
+                        if (pos == 0)
+                        {
+                            // Make sure that we consume at least one glyph.
+                            // So this element will overflow
+                            currentWidth = nextWidth;
+                        }
+                        else
+                        {
+                            // We didn't consume the glyph, it's for the next line
+                            nextBreak = pos;
+                        }
+                        break;
+                    }
+                    currentWidth = nextWidth;
+                } while (nextBreak < to);
+                // Now we either processed the whole text or we need to break
+                container.addElementNoLineBreak(getTextLayoutElement(
+                    word.sliced(actualStart, nextBreak), currentWidth.toReal(),
+                    !needsBreak && this->hasTrailingSpace()));
+                if (needsBreak)
+                {
+                    container.breakLine();
+                }
+
+                actualStart += nextBreak;
+                // Update the view
+                view = QString::fromRawData(word.constData() + actualStart,
+                                            word.size() - actualStart);
+                assert(needsBreak || view.isEmpty());
+            } while (!view.isEmpty());
+#else
             auto textLength = word.length();
             int wordStart = 0;
             width = 0;
 
-            // QChar::isHighSurrogate(text[0].unicode()) ? 2 : 1
-
             for (int i = 0; i < textLength; i++)
             {
                 auto isSurrogate = word.size() > i + 1 &&
@@ -663,6 +747,7 @@ void TextElement::addToContainer(MessageLayoutContainer &container,
             //add the final piece of wrapped text
             container.addElementNoLineBreak(getTextLayoutElement(
                 word.mid(wordStart), width, this->hasTrailingSpace()));
+#endif
         }
     }
 }