My strategy when centering text on images is to get bounding rectangle for that text and divide width or height by two. I did the same in this case. This is example I have created:
void CanvasWidget::paintEvent(QPaintEvent*)
{
//Create image:
QImage image(rect().width(), rect().height(), QImage::Format_RGB32);
QPainter paint(&image);
// White background
image.fill(QColor("#FFF"));
// set some metrics, position and the text to draw
QFontMetrics metrics = paint.fontMetrics();
int yposition = 100;
QString text = "Hello world.";
// Draw gray line to easily see if centering worked
paint.setPen(QPen(QColor("#666"), 1, Qt::SolidLine, Qt::FlatCap, Qt::RoundJoin));
paint.drawLine(0, yposition, image.width(), yposition);
// Get rectangle
QRect fontRect = metrics.boundingRect(text);
// Black text
paint.setPen(QPen(QColor("#000"), 1, Qt::SolidLine, Qt::FlatCap, Qt::RoundJoin));
// Add half the height to position (note that Qt has [0,0] coordinates at the bottom of the image
paint.drawText(4, yposition+round(((double)fontRect.height())/2.0), text);
QPainter p(this);
p.drawImage(rect(), image, image.rect());
p.end();
}
This is the result - the text is under line instead centered on the line:
Android:
Windows:
I used lines to draw frame around the text based on metrics rectangle:
Intended result was to center visible text exactly around the given point/line:
To put you in perspective, this is the actual problem I am having:
The numbers should be in the middle of the lines, not so much below.
The function I am using returns size including accents and other big characters that aren't there. How do I get the rectangle in pixels only for characters that are there?
Not quite sure what you're asking, but if it's why does the bounding rect appear wrong, it's because you're not taking into account characters that have accents in the font such as é, å etc. The bounding rect returned from font metrics includes these.
As it states in the boundingRect documentation
The height of the bounding rectangle is at least as large as the value returned by height().
This is not the case for tightBoundingRect that will, I expect, provide the right result.
Related
I am required to create text items with exact width and height of text contents.
The height of the text is the most important requirement.
The position of the text should be relative to the text itself.
I also have to be able to place it on canvas in an exact spot.
Assuming a (printable) canvas (on a larger QGraphicsScene), say 5 inch width and 1 inch height, my text should be able to stretch top-bottom-left-right - and be placed on canvas, not part in part out.
I am sub-classing QGraphicsTextItem for my item type. I am resizing it, using QTransform(), to required size - in inches or mm or pixels (72*in).
Also setting the document() margin to 0, and anything inside (like QTextBlockFormat margins) also to 0.
I have implemented a setItemSize(QSizeF sz) (with sz in pixels), that resizes the QGraphicsTextItem as required.
The sz is initialized using the item bounding rect.
Assuming no wrap, single line text (multi-line could be solved separately once this issue is resolved).
When adding the item to canvas, I still see a top and bottom margin - and this varies based on font choice.
I drew a rectangle around the item to see it.
The top/bottom distances depend on font choices.
I have tried to use font metrics to determine these distances (in paint() I have been drawing lines to try to determine the position and rectangle in which the text fits).
I would be happy to at least be able to determine correct size to use for upper case, no accents or special characters fonts (it would be a start, though naturally I would need to be able to use any characters).
But at least some way to determine the size and position (relative to the (0,0) of item) of the text content even in the simplest case.....
The font metrics tightBoundingRect() seems the most accurate for size, but it seems impossible to determine its position so that I can somehow create my items correctly, and maybe resize/shift them correctly to fit on canvas.
Here are some examples of my struggle to determine at least exact size and position of text, relative to the (0,0) of the item (assuming that once I do that, I am able to expose that info to outside or include the shift in the item transform on resize).
Notice that the size of the text advertised by font metrics does not always cover the text, and for different fonts I am not able to position the tight bounding rect (magenta) around the text itself. (I did multiple guesses, the code below is just one - the lines are trying to show different font metrics sizes).
The above were experiments in paint function of the text item inheriting QGraphicsTextItem:
void paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget)
{
// draw text
QGraphicsTextItem::paint(painter, option, widget);
QPen p;
p.setWidthF(0);
QFontMetricsF fm(this->font());
qreal ascent = fm.ascent(),
descent = fm.descent(),
hheight = fm.height();
QRectF r = QGraphicsTextItem::boundingRect();
QRectF rFont= fm.tightBoundingRect(toPlainText());
qreal xmax = r.right();
painter->save();
painter->setBrush(Qt::NoBrush);
// where is "ascent + descent"
p.setColor(Qt::green);
painter->setPen(p);
painter->drawLine(QPointF(2, ascent), QPointF(2, ascent + descent));
painter->drawLine(QPointF(2, ascent + descent), QPointF(xmax/2, ascent + descent));
// where is "height"
p.setColor(Qt::red);
painter->setPen(p);
painter->drawLine(QPointF(xmax/2, 0), QPointF(xmax/2, hheight));
painter->drawLine(QPointF(xmax/2, ascent + descent), QPointF(xmax, ascent + descent));
// where is "ascent"
p.setColor(Qt::yellow);
painter->setPen(p);
painter->drawLine(QPointF(6, 0), QPointF(6, ascent));
painter->drawLine(QPointF(6, ascent), QPointF(xmax, ascent));
// something that may look like top of the text
p.setColor(Qt::blue);
painter->setPen(p);
qreal yyy = ascent + rFont.y() + 1;
painter->drawLine(QPointF(5, yyy), QPointF(xmax, yyy));
// this should be useful... should be the natural offset
qreal yoffset = (r.height() - rFont.height()) / 2;
// qDebug() << yoffset << r << rFont;
//qreal y0 = (r.height() - fm.height())/2;
p.setColor(Qt::darkGreen);
painter->drawEllipse(10, yoffset, 1, 1);
// where is the font rect
p.setColor(Qt::magenta);
painter->setPen(p);
yoffset = (r.height() + rFont.height()) / 2;
painter->translate(0, yoffset);
painter->drawRect(rFont);
painter->restore();
}
I have also tried not using QGraphicsTextItem, but paint text inside a rectangle. The same thing happens.
(Qt 4.7 - 5.x)
This is not a good solution. This is an attempt to solve my own problem - in a first iteration - of setting text with given width and height, using font metrics.
Reasons for not being good -
Even after resize, text is smaller than desired, I don't understand why
The position is incorrect, based on font style the text can be above or below the canvas, meaning it gets clipped.
I resize it using a factor calculated from the item bounding rect size and the font metrics bounding rect (I used the tight bounding rect for more accurate size).
myText->setItemFontSize(12); // If I use font metrics I need to reset text size on every change, because resizing loses font info
QFontMetricsF fm(myText->font());
QRectF fmRect = fm.tightBoundingRect(myText.toPlainText().toUpper());
// without toUpper() the size is too small - even so it is a bit small
// I read tightBoundingRect is slow - but boundingRect and height and ascent all give values that result in even smaller size
//qreal absH = fm.ascent();
qreal absH = fmRect.height();
qreal absW = fmRect.width();
qreal absHeightRatio = myText->getItemSize().height() / absH;
qreal absWidthRatio = myText->getItemSize().width() / absW;
Then setting size:
myText->setItemSize(QSizeF(absWidthRatio * textLength, absHeightRatio * fontHeight));
// This function scales the `QTransform` on item
// but since I request a final position dependent on item size
// (including blank space around it) - it has no chance of being accurate.....
// This is where my next effort will go, figuring out how to get rid of the fluff
// around the item inside the scaling
The function for setting position: trying to center text:
// leftShift = 10, rightShift = 10 in example
myText->setPos(0,0);
QRectF r = myText->mapToScene(myText->boundingRect()).boundingRect();
QSizeF sz = r.size();
qreal w = sz.width();
qreal h = sz.height();
qreal cx = (m_docLength - w + leftShift - rightShift)/2 - r.left();
qreal cy = (m_docHeight - h)/2 - r.top();
myText->setPos(cx, cy);
The images below are for fontHeight = m_docHeight -
Desirable:
- either the entire size of text (ascent + descent) equals doc height, and text is centered vertically based on content
- or the upper case size text equals doc height and the descent is below document (text centered based on only upper case) - this would seem easier based on how QGraphicsTextItem seems to position it
Actual:
- the text is smaller no matter which parameters I use to scale, and centered based on upper case text
As shown above - I have no idea how I could center vertically based on content (so for edge-to-edge text the descent would fit in) - and in lieu of that, all I really want is edge-to-edge uppercase letters, but I can't seem able to achieve that.
Oh and these are for Arial type font - one of the best-behaved. Other fonts jump all over the place, either above or below the canvas. And for some fonts, the resulting text is actually smaller - which is inexplicable to me, because how can the tight bounding rectangle be smaller than the item bounding rectangle...
Still this is as far as I got to getting my text as close to "true" size and placed on a canvas that matches its size.
1) How can I wrap text in a QGraphicsTextItem to fit a fixed rectangle, with width and height ?
Right now I am experimenting with creating a text, getting its bounding rectangle, and resizing it to fit the box - but I can't get wrapping.
class TTT: public QGraphicsTextItem {
TTT() {
{
setPlainText("abcd");
qreal x = m_itemSize.width()/boundingRect().width();
qreal y = m_itemSize.height()/boundingRect().height();
scale(x, y);
}
void paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget) {
// experiment with clip regions
// text gets covered by hole in clip
QRegion r0(boundingRect().toRect());
QRegion r1(QRect(5, 5, 10, 10), QRegion::Ellipse);
QRegion r2 = r0.subtracted(r1);
painter->setClipRegion(r2);
painter->setBrush(Qt::yellow);
painter->drawRect(boundingRect());
QGraphicsTextItem::paint(painter, option, widget);
}
}
What makes wrapping happen, how can I trigger it ?
Right now, as I keep typing, the box is automatically expanding.
2) Is it possible to wrap the text in a QGraphicsItem / QGraphicTextItem subclass in a shape that is not a rectangle ?
(Something like in the image above)
I tried to use clipRegion, see code above, but I guess it is not the right way to go, clipping cuts the text but did not wrap.
Maybe it would... If I could figure out how to wrap text in the first place ?
Qt 4.8
You did not specify Qt version but try:
void QGraphicsTextItem::setTextWidth(qreal width)
Sets the preferred width for the item's text. If the actual text is wider than >the specified width then it will be broken into multiple lines.
If width is set to -1 then the text will not be broken into multiple lines >unless it is enforced through an explicit line break or a new paragraph.
The default value is -1.
In answer to 1) I'd opt not to use the QGraphicsTextItem, but draw the text directly in your QGraphicsItem's paint function using the drawText overloaded function, which takes a QTextOption parameter.
Using this, you can set the WrapMode, for example, with a call to
QTextOption::setWrapMode(QTextOption:: WordWrap)
As for 2) with a non-rectangular shape, I don't think Qt will do this for you.
Doing it yourself you can use QFontMetrics, to work out just how much text would fit in each line, depending upon where it lies within its bounding item.
Alternatively, you could adapt the concept of a text-to-path method.
I am trying to customize a QPUshButton by subclassing it and overriding the paintEvent. I am writing the text, followed by the icon as below:
paintEvent(QPaintEvent *paint)
{
QStyleOption opt;
opt.init(this);
QPainter p(this);
//Draw the base
style()->drawPrimitive(QStyle::PE_Widget, &opt, &p, this);
//Draw the text
style()->drawItemText(&p,this->rect(),Qt::AlignCenter,(this->palette()), true, this->text());
//How do I make the image immediately follow the text
if(!this->icon().isNull())
//Draw the icon at 75% button height
style()->drawItemPixmap(&p, this->rect(),Qt::AlignRight|Qt::AlignVCenter, this->icon().pixmap(this->rect().height() * 0.75));
}
I am center aligning the text, and right aligning the icon. However, this causes a gap between the text and the icon. Is there any way for me to draw the icon immediately after the text, instead of aligning?
In other words, is there any way to get the position where the drawItemText finished?
QStyle::itemTextRect() will tell you where the text will be laid down with given rectangle, font metrics and alignment.
QFontMetrics will tell you how wide your text is. It doesn't know about your rectangle, so you will have to do the alignment calculation yourself.
I am rendering a QPixmap inside of a QThread. the code to paint is inside a function. If I declare the painter inside the drawChart function everything seems ok but if I declare the painter inside the run function the image is wrong in the sense that at the edge of a black and white area, the pixels at the interface are overlapped to give a grey. Does anyone know why this is so? Could it be because of the nature of the run function itself?
//This is ok
void RenderThread::run()
{
QImage image(resultSize, QImage::Format_RGB32);
drawChart(&image);
emit renderedImage(image, scaleFactor);
}
drawChart(&image)
{
QPainter painter(image);
painter.doStuff()(;
...
}
//This gives a image that seems to have artifacts
void RenderThread::run()
{
QImage image(resultSize, QImage::Format_RGB32);
QPainter painter(image);
drawChart(painter);
emit renderedImage(image, scaleFactor);
}
drawChart(&painter)
{
painter.doStuff();
...
}
//bad
.
//good
.
From C++ GUI Programming with Qt 4 by Jasmin Blanchette and Mark Summerfield:
One important thing to understand is
that the center of a pixel lies on
“half-pixel” coordinates. For example,
the top-left pixel covers the area
between points (0, 0) and (1, 1), and
its center is located at (0.5, 0.5).
If we ask QPainter to draw a pixel at,
say, (100, 100), it will approximate
the result by shifting the coordinate
by +0.5 in both directions, resulting
in the pixel centered at (100.5,
100.5) being drawn.
This distinction may seem rather
academic at first, but it has
important consequences in practice.
First, the shifting by +0.5 only
occurs if antialiasing is disabled
(the default); if antialiasing is
enabled and we try to draw a pixel at
(100, 100) in black, QPainter will
actually color the four pixels (99.5,
99.5), (99.5, 100.5), (100.5, 99.5), and (100.5, 100.5) light gray, to give
the impression of a pixel lying
exactly at the meeting point of the
four pixels. If this effect is
undesirable, we can avoid it by
specifying half-pixel coordinates, for
example, (100.5, 100.5).
I need to do some emulation of some old DOS or mainframe terminals in Flex. Something like the image below for example.
The different coloured text is easy enough, but the ability to do different background colours, such as the yellow background is beyond the capabilities of the standard Flash text.
I may also need to be able to enter text at certain places and scroll text up the "terminal". Any idea how I'd attack this? Or better still, any existing code/components for this sort of thing?
Use TextField.getCharBoundaries to get a rectangle of the first and last characters in the areas where you want a background. From these rectangles you can construct a rectangle that spans the whole area. Use this to draw the background in a Shape placed behind the text field, or in the parent of the text field.
Update you asked for an example, here is how to get a rectangle from a range of characters:
var firstCharBounds : Rectangle = textField.getCharBoundaries(firstCharIndex);
var lastCharBounds : Rectangle = textField.getCharBoundaries(lastCharIndex);
var rangeBounds : Rectangle = new Rectangle();
rangeBounds.topLeft = firstCharBounds.topLeft;
rangeBounds.bottomRight = lastCharBounds.bottomRight;
If you want to find a rectangle for a whole line you can do this instead:
var charBounds : Rectangle = textField.getCharBoundaries(textField.getLineOffset(lineNumber));
var lineBounds : Rectangle = new Rectangle(0, charBounds.y, textField.width, firstCharBounds.height);
When you have the bounds of the text range you want to paint a background for, you can do this in the updateDisplayList method of the parent of the text field (assuming the text field is positioned at [0, 0] and has white text, and that textRangesWithYellowBackground is an array of rectangles that represent the text ranges that should have yellow backgrounds):
graphics.clear();
// this draws the black background
graphics.beginFill(0x000000);
graphics.drawRect(0, 0, textField.width, textField.height);
graphics.endFill();
// this draws yellow text backgrounds
for each ( var r : Rectangle in textRangesWithYellowBackground )
graphics.beginFill(0xFFFF00);
graphics.drawRect(r.x, r.y, r.width, r.height);
graphics.endFill();
}
The font is fixed width and height, so making a background bitmap dynamically isn't difficult, and is probably the quickest and easiest solution. In fact, if you size it correctly there will only be one stretched pixel per character.
Color the pixel (or pixels) according to the background of the character.
-Adam