Fix outline for connected text

For any font where glyphs are connected (any font could
have this, but specifically Arabic and Indic fonts will
typically always connect glyphs, as it is required to
express the language correctly), we would draw the outline
on a per-glyph basis, thus getting outlines that disconnect
the glyphs.

In order to fix this, we have to draw the fill of the glyphs
in a separate pass after the outline has been drawn.

Note that in order for this to look correct, we have to
disable subpixel antialiasing on the fill, which required
some plumbing in the native rendering glyph node. The
outline shaders have also been changed to only draw the
outline and not the fill.

[ChangeLog][QtQuick][Text] Fixed Outline style on connected glyphs,
especially visible in e.g. Arabic and Indic writing systems.

Pick-to: 5.15
Fixes: QTBUG-69301
Fixes: QTBUG-83358
Change-Id: If52a940bfb0267384ea002120655aed1310458a1
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

1 files changed, 29 insertions, 1 deletions

diff --git a/src/quick/scenegraph/qsgdefaultglyphnode.cpp b/src/quick/scenegraph/qsgdefaultglyphnode.cpp
index 5bd5cc4891..d3e0d5a7c5 100644
--- a/src/quick/scenegraph/qsgdefaultglyphnode.cpp
+++ b/src/quick/scenegraph/qsgdefaultglyphnode.cpp
@@ -40,12 +40,15 @@
 #include "qsgdefaultglyphnode_p.h"
 #include "qsgdefaultglyphnode_p_p.h"
 
+#include <private/qrawfont_p.h>
+
 QT_BEGIN_NAMESPACE
 
 QSGDefaultGlyphNode::QSGDefaultGlyphNode(QSGRenderContext *context)
     : m_context(context)
     , m_glyphNodeType(RootGlyphNode)
     , m_dirtyGeometry(false)
+    , m_preferredAntialiasingMode(DefaultAntialiasing)
 {
     setFlag(UsePreprocess);
 }
@@ -59,6 +62,11 @@ QSGDefaultGlyphNode::~QSGDefaultGlyphNode()
     m_nodesToDelete.clear();
 }
 
+void QSGDefaultGlyphNode::setPreferredAntialiasingMode(AntialiasingMode mode)
+{
+    m_preferredAntialiasingMode = mode;
+}
+
 void QSGDefaultGlyphNode::setMaterialColor(const QColor &color)
 {
     static_cast<QSGTextMaskMaterial *>(m_material)->setColor(color);
@@ -76,7 +84,27 @@ void QSGDefaultGlyphNode::update()
     QMargins margins(0, 0, 0, 0);
 
     if (m_style == QQuickText::Normal) {
-        m_material = new QSGTextMaskMaterial(m_context, QVector4D(m_color.redF(), m_color.greenF(), m_color.blueF(), m_color.alphaF()), font);
+        QFontEngine::GlyphFormat glyphFormat;
+
+        // Don't try to override glyph format of color fonts
+        if (QRawFontPrivate::get(font)->fontEngine->glyphFormat == QFontEngine::Format_ARGB) {
+            glyphFormat = QFontEngine::Format_None;
+        } else {
+            switch (m_preferredAntialiasingMode) {
+            case GrayAntialiasing:
+                glyphFormat = QFontEngine::Format_A8;
+                break;
+            case HighQualitySubPixelAntialiasing:
+            case LowQualitySubPixelAntialiasing:
+                glyphFormat = QFontEngine::Format_A32;
+                break;
+            default:
+                glyphFormat = QFontEngine::Format_None;
+                break;
+            }
+        }
+
+        m_material = new QSGTextMaskMaterial(m_context, QVector4D(m_color.redF(), m_color.greenF(), m_color.blueF(), m_color.alphaF()), font, glyphFormat);
     } else if (m_style == QQuickText::Outline) {
         QSGOutlinedTextMaterial *material = new QSGOutlinedTextMaterial(m_context, font);
         material->setStyleColor(m_styleColor);