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Workaround qt bug which causes word spacing to shrink to nothing
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when very large font sizes are rendered

Works around https://bugreports.qt.io/browse/QTBUG-98778
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@nyalldawson
nyalldawson committed Dec 1, 2021
1 parent e4e2451 commit fa5c53e
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Showing 4 changed files with 47 additions and 11 deletions.
34 changes: 27 additions & 7 deletions src/core/textrenderer/qgstextrenderer.cpp
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Expand Up @@ -307,7 +307,7 @@ double QgsTextRenderer::drawBuffer( QgsRenderContext &context, const QgsTextRend

const double penSize = context.convertToPainterUnits( buffer.size(), buffer.sizeUnit(), buffer.sizeMapUnitScale() );

const double scaleFactor = ( context.flags() & Qgis::RenderContextFlag::ApplyScalingWorkaroundForTextRendering ) ? FONT_WORKAROUND_SCALE : 1.0;
const double scaleFactor = calculateScaleFactorForFormat( context, format );

std::optional< QgsScopedRenderContextReferenceScaleOverride > referenceScaleOverride;
if ( mode == Label )
Expand Down Expand Up @@ -464,7 +464,7 @@ void QgsTextRenderer::drawMask( QgsRenderContext &context, const QgsTextRenderer
QPainterPath path;
path.setFillRule( Qt::WindingFill );

const double scaleFactor = ( context.flags() & Qgis::RenderContextFlag::ApplyScalingWorkaroundForTextRendering ) ? FONT_WORKAROUND_SCALE : 1.0;
const double scaleFactor = calculateScaleFactorForFormat( context, format );

// TODO: vertical text mode was ignored when masking feature was added.
// Hopefully Oslandia come back and fix this? Hint hint...
Expand Down Expand Up @@ -555,7 +555,7 @@ double QgsTextRenderer::textWidth( const QgsRenderContext &context, const QgsTex
double QgsTextRenderer::textWidth( const QgsRenderContext &context, const QgsTextFormat &format, const QgsTextDocument &document )
{
//calculate max width of text lines
const double scaleFactor = ( context.flags() & Qgis::RenderContextFlag::ApplyScalingWorkaroundForTextRendering ) ? FONT_WORKAROUND_SCALE : 1.0;
const double scaleFactor = calculateScaleFactorForFormat( context, format );

bool isNullSize = false;
const QFont baseFont = format.scaledFont( context, scaleFactor, &isNullSize );
Expand Down Expand Up @@ -639,7 +639,7 @@ double QgsTextRenderer::textHeight( const QgsRenderContext &context, const QgsTe

double QgsTextRenderer::textHeight( const QgsRenderContext &context, const QgsTextFormat &format, QChar character, bool includeEffects )
{
const double scaleFactor = ( context.flags() & Qgis::RenderContextFlag::ApplyScalingWorkaroundForTextRendering ) ? FONT_WORKAROUND_SCALE : 1.0;
const double scaleFactor = calculateScaleFactorForFormat( context, format );
bool isNullSize = false;
const QFont baseFont = format.scaledFont( context, scaleFactor, &isNullSize );
if ( isNullSize )
Expand Down Expand Up @@ -754,7 +754,7 @@ double QgsTextRenderer::textHeight( const QgsRenderContext &context, const QgsTe
document.applyCapitalization( format.capitalization() );

//calculate max height of text lines
const double scaleFactor = ( context.flags() & Qgis::RenderContextFlag::ApplyScalingWorkaroundForTextRendering ) ? FONT_WORKAROUND_SCALE : 1.0;
const double scaleFactor = calculateScaleFactorForFormat( context, format );

bool isNullSize = false;
const QFont baseFont = format.scaledFont( context, scaleFactor, &isNullSize );
Expand Down Expand Up @@ -881,7 +881,7 @@ void QgsTextRenderer::drawBackground( QgsRenderContext &context, QgsTextRenderer
component.rotationOffset = background.rotation();
}

const double scaleFactor = ( context.flags() & Qgis::RenderContextFlag::ApplyScalingWorkaroundForTextRendering ) ? FONT_WORKAROUND_SCALE : 1;
const double scaleFactor = calculateScaleFactorForFormat( context, format );

if ( mode != Label )
{
Expand Down Expand Up @@ -1409,7 +1409,7 @@ void QgsTextRenderer::drawTextInternal( TextPart drawType,
std::unique_ptr< QFontMetricsF > tmpMetrics;
if ( !fontMetrics )
{
fontScale = ( context.flags() & Qgis::RenderContextFlag::ApplyScalingWorkaroundForTextRendering ) ? FONT_WORKAROUND_SCALE : 1.0;
fontScale = calculateScaleFactorForFormat( context, format );

std::optional< QgsScopedRenderContextReferenceScaleOverride > referenceScaleOverride;
if ( mode == Label )
Expand Down Expand Up @@ -2071,3 +2071,23 @@ void QgsTextRenderer::drawTextInternalVertical( QgsRenderContext &context, const
}
}

double QgsTextRenderer::calculateScaleFactorForFormat( const QgsRenderContext &context, const QgsTextFormat &format )
{
if ( !( context.flags() & Qgis::RenderContextFlag::ApplyScalingWorkaroundForTextRendering ) )
return 1.0;

const double pixelSize = context.convertToPainterUnits( format.size(), format.sizeUnit(), format.sizeMapUnitScale() );

// THESE THRESHOLD MAY NEED TWEAKING!

// for small font sizes we need to apply a growth scaling workaround designed to stablise the rendering of small font sizes
if ( pixelSize < 50 )
return FONT_WORKAROUND_SCALE;
//... but for font sizes we might run into https://bugreports.qt.io/browse/QTBUG-98778, which messes up the spacing between words for large fonts!
// so instead we scale down the painter so that we render the text at 200 pixel size and let painter scaling handle making it the correct size
else if ( pixelSize > 200 )
return 200 / pixelSize;
else
return 1.0;
}

2 changes: 2 additions & 0 deletions src/core/textrenderer/qgstextrenderer.h
View file
Expand Up @@ -401,6 +401,8 @@ class CORE_EXPORT QgsTextRenderer
VAlignment vAlignment,
double rotation );

static double calculateScaleFactorForFormat( const QgsRenderContext &context, const QgsTextFormat &format );

friend class QgsVectorLayerLabelProvider;
friend class QgsLabelPreview;

Expand Down
22 changes: 18 additions & 4 deletions tests/src/python/test_qgstextrenderer.py
View file
Expand Up @@ -1438,9 +1438,10 @@ def checkRender(self, format, name, part=None, angle=0, alignment=QgsTextRendere
text=['test'],
rect=QRectF(100, 100, 50, 250),
vAlignment=QgsTextRenderer.AlignTop,
flags=Qgis.TextRendererFlags()):
flags=Qgis.TextRendererFlags(),
image_size=400):

image = QImage(400, 400, QImage.Format_RGB32)
image = QImage(image_size, image_size, QImage.Format_RGB32)

painter = QPainter()
ms = QgsMapSettings()
Expand Down Expand Up @@ -1492,8 +1493,9 @@ def checkRender(self, format, name, part=None, angle=0, alignment=QgsTextRendere

def checkRenderPoint(self, format, name, part=None, angle=0, alignment=QgsTextRenderer.AlignLeft,
text=['test'],
point=QPointF(100, 200)):
image = QImage(400, 400, QImage.Format_RGB32)
point=QPointF(100, 200),
image_size=400):
image = QImage(image_size, image_size, QImage.Format_RGB32)

painter = QPainter()
ms = QgsMapSettings()
Expand Down Expand Up @@ -1536,6 +1538,18 @@ def checkRenderPoint(self, format, name, part=None, angle=0, alignment=QgsTextRe
painter.end()
return self.imageCheck(name, name, image)

def testDrawMassiveFont(self):
"""
Test that we aren't bitten by https://bugreports.qt.io/browse/QTBUG-98778
This test should pass when there's a correct WORD space between the 'a' and 't' characters, or fail when
the spacing between these characters is nill or close to a letter spacing
"""
format = QgsTextFormat()
format.setFont(getTestFont('bold'))
format.setSize(1100)
assert self.checkRender(format, 'massive_font', rect=QRectF(-800, -600, 1000, 1000), text=['a t'], image_size=800)

@unittest.skipIf(int(QT_VERSION_STR.split('.')[0]) < 6 or (int(QT_VERSION_STR.split('.')[0]) == 6 and int(QT_VERSION_STR.split('.')[1]) < 3), 'Too old Qt')
def testDrawSmallCaps(self):
format = QgsTextFormat()
Expand Down
Binary file added tests/testdata/control_images/text_renderer/massive_font/massive_font.png
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