I have a QWidget inside a window. The window can be resized and the widget should stretch to cover the maximum area possible. I'm drawing a plot onto this QWidget and I want the plot to stretch with the window. Currently it works, but I feel I could be doing this way cleaner.
This is how it looks:
After resizing this is what I want it to look like:
Currently this works, but I'm doing it like this:
In the widgets paintEvent() I calculate the scale factor like this
double scaleFactorX = (double) width() / m_xAxis.last();
double scaleFactorY = (double) height() / m_yAxis.last();
*Note that m_xAxis.last() is the largest value that will be plotted. And width() and height() return the width and height of the QWidget.
Then when I'm drawing the elements I multiply each point with the scale factor to stretch it to the width of the QWidget. I feel like there's a better (more correct) way of doing this, but I'm not sure what to do.
Any help would be appreciated.
You can do this in an easier / more readable way using by setting a QTransform on your QPainter.
Example from the doc (of course you're probably more interested in .scale() than in .translate()):
void CombinedTransformation::paintEvent(QPaintEvent *)
{
QPainter painter(this);
painter.setPen(QPen(Qt::blue, 1, Qt::DashLine));
painter.drawRect(0, 0, 100, 100);
QTransform transform;
transform.translate(50, 50);
transform.rotate(45);
transform.scale(0.5, 1.0);
painter.setTransform(transform);
painter.setFont(QFont("Helvetica", 24));
painter.setPen(QPen(Qt::black, 1));
painter.drawText(20, 10, "QTransform");
}
Related
I'm trying to show a rounded avatar QPixMap with a white border around it. However, I have no clue as to how I could add the border... Is it even possible?
This is the function I have to draw the avatar image.
void AccountDropDownMenu::setAvatar(
const QByteArray& bytes)
{
QPixmap new_avatar;
new_avatar.loadFromData(bytes);
new_avatar = new_avatar.scaledToHeight(40, Qt::SmoothTransformation);
QBitmap map(new_avatar.size());
map.fill(Qt::color0);
QPainter painter(&map);
painter.setRenderHint(QPainter::Antialiasing);
painter.setBrush(Qt::color1);
painter.setPen(QPen(Qt::white, 10));
painter.drawRoundedRect(
m_avatar_label->x(),
m_avatar_label->y(),
new_avatar.width(),
new_avatar.height(),
45,
45);
new_avatar.setMask(map);
avatar_label->setPixmap(new_avatar);
}
Update
Thanks to dtech I was able to get the desired output using the following updated function.... Although it's a bit pixly (the border).
void AccountDropDownMenu::setAvatar(
const QByteArray& bytes)
{
QPixmap new_avatar;
new_avatar.loadFromData(bytes);
new_avatar = new_avatar.scaledToHeight(40, Qt::SmoothTransformation);
QBitmap map(new_avatar.size());
map.fill(Qt::color0);
QPainter painter(&map);
painter.setRenderHint(QPainter::Antialiasing);
painter.setBrush(Qt::color1);
painter.drawRoundedRect(
QRectF(
avatar_label->x(),
avatar_label->y(),
new_avatar.width(),
new_avatar.height()),
40,
40);
new_avatar.setMask(map);
QPainter painter2(&new_avatar);
painter2.setRenderHint(QPainter::Antialiasing);
painter2.setPen(QPen(Qt::white, 1));
painter2.drawRoundedRect(
QRectF(
avatar_label->x(),
avatar_label->y(),
new_avatar.width(),
new_avatar.height()),
40,
40);
avatar_label->setPixmap(new_avatar);
}
In Qt you draw fills with a brush, but outlines are drawn with a QPen.
I haven't used QPainter in a long time, but IIRC, the default pen is zero width, which would explain why you aren't getting anything - you are not setting a pen.
Also, you don't need "another" rounded rectangle, you can apply fill and outline to the same geometry, as demonstrated in this answer.
Update:
Your updated code sets a mask, which sets an alpha channel. That cuts away from what you already have, it could not possibly add anything. You have to paint on the pixmap. Simply use new_avatar as the paint device - QPainter painter(&new_avatar); and get rid of the rest.
I'm writing a gauge widget, using QT, that is constructed from 2 separate images, one as background and the other as Needle. I reimplement paintEvent function as follow:
void myGaugeWidget::paintEvent(QPaintEvent *pe)
{
QPainter painter(this);
QPixmap bkgImage(bkgImgPath);
painter.drawPixmap(0, 0, width(), height(), bkgImage);
const double thetaDeg = 30.0;
QPixmap needle(needles[i].imgPath);
int needleWidth = 200;
int needleHeight = 200;
int anchorX = 20;
int anchorY = 30;
const int centerX = width()/2;
const int centerY = height()/2;
QTransform rm = QTransform().translate(-anchorX,- anchorY).rotate(thetaDeg).translate(centerX,centerY);
needle = needle.transformed(rm);
painter.drawPixmap(0,0, needle);
}
this code rotates my needle correctly but its position is not correct.
can anybody help me?
thanks.
This most likely would depend on your images and widget size. I have tried your code and it seems to me that QTransform().translate() is not doing anything in a QPixmap. I tried to give extreme values for translate() and removed rotate() - the image does not move.
I already have have my own implementation for a gauge. This is with painter transformation instead of the image. My images are of dimensions:
Gauge Background: 252x252 (there is some external blurring effects around the circle boundaries, making the background image larger than it seems)
Needle: 7x72 ( the image dimensions wrap around the boundaries of the needle itself)
Needle roation center (with respect to the background): 126, 126 (divide background size by 2)
The needle image points upward
For this setup, here is my paintEvent() with some explanations:
void myGaugeWidget::paintEvent(QPaintEvent *)
{
QPainter painter(this);
painter.setRenderHint(QPainter::Antialiasing);
//draw the background which is same size as the widget.
painter.drawPixmap(0, 0, bg.width(), bg.height(), bg);
//Calculate the angle of rotation.
//The gauge I am using has a cutout angle of 120 degrees at the bottom (symmetric)
float needleAngle = -120/*offset for start rotation*/ + ((value-minValue)*240/*total sweep of the gauge*//(maxValue-minValue));
painter.save();
//translate the painter to the roation center and then perform the rotation
painter.translate(126, 126);
painter.rotate(needleAngle);
//translate the rotated canvas to adjust for the height of the needle.
//If you don't do this, your needle's tip will be at the rotation center
painter.translate(0, -72);
//draw the needle and adjust for the width with the x value
painter.drawPixmap(-needle.width()/2, 0, needle.width(), needle.height(), needle);
painter.restore();
}
I have overriden updatePaintNode in the following way to draw an OpenGL texture on a QQuickItem derived class called MyQQuickItem here.
QSGNode *MyQQuickItem::updatePaintNode(QSGNode * oldNode, QQuickItem::UpdatePaintNodeData * /*updatePaintNodeData*/)
{
QSGSimpleTextureNode * textureNode = static_cast<QSGSimpleTextureNode *>(oldNode);
if (!textureNode) {
textureNode = new QSGSimpleTextureNode();
}
QSize size(800, 800);
// myTextureId is a GLuint here
textureNode.reset(window()->createTextureFromId(myTextureId, size));
textureNode->setTexture(my_texture);
textureNode->markDirty(QSGBasicGeometryNode::DirtyMaterial);
QSizeF myiewport = boundingRect().size();
qreal xOffset = 0;
qreal yOffset = 10;
textureNode->setRect(xOffset, yOffset, myViewport.width(), myViewport.height());
return textureNode;
}
This renders the texture content well but covers the whole of my MyQQuickItem UI.
How can reduce the bottom margin of the texture to say fit 80% of the height of MyQQuickItem.
I want to render the texture to a portion of MyQQuickItem & leave the rest blank or black? Is that possible within updatePaintNode.
Note that the texture size is not the UI window size here. My texture size is 800 by 800. Whereas the UI window size is different and depends on the screen.
I found the answer to this:
Changing myViewport.height() gives the required end in Y direction one wishes to set. Similarly, changing myViewport.width() gives the required end in X direction one wishes to set.
4 parameters in TextureNode's setRect can stretch & fit the texture in the way one wishes within a portion of the QQuickItem.
I have a number of classes that inherit from QGraphicsItem, that get to be arranged in a certain way. For simplicity of calculations, I made the scenes, and items, centered in (0, 0) (with the boundingRect() having +/- coordinates).
QGraphicsTextItem subclass defies me, its pos() is relative to top left point.
I have tried a number of things to shift it so it centers in the text center (for example, the suggested solution here - the code referenced actually cuts my text and only shows the bottom left quarter).
I imagined that the solution should be something simple, like
void TextItem::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget)
{
painter->translate( -boundingRect().width()/2.0, -boundingRect().height()/2.0 );
QGraphicsTextItem::paint(painter, option, widget );
}
the above "sort of" works - but as I increase the item scale -> increase the font, the displayed item is cut off...
I tried to set the pos() - but the problem is, I still need to track the actual position on the scene, so I cannot just replace it.
A slightly unpleasant side effect - centering the QGraphicsView on the element does not work either.
How can I make my QGraphicsTextItem show its position relative to the center of the text ?
Edit: one of the experiments of changing the boundingRect():
QRectF TextItem::boundingRect() const
{
QRectF rect = QGraphicsTextItem::boundingRect();
rect.translate(QPointF(-rect.width()/2.0, -rect.height()/2.0));
return rect;
}
I had to shift the initial position, as well as the resize, to trigger a new position - I was unable to do it in paint() because, as I thought from the start, any repaint would continuously recalculate the position.
Only the initial position needs to be adjusted - but as the font size (or style...) changes, its bounding rectangle also changes, so the position must be recalculated - based on previous position.
In the constructor,
setPos(- boundingRect().width()/2, - boundingRect().height()/2);
in the function that modifies item (font) size,
void TextItem::setSize(int s)
{
QRectF oldRect = boundingRect();
QFont f;
f.setPointSize(s);
setFont(f);
if(m_scale != s)
{
m_scale = s;
qreal x = pos().x() - boundingRect().width()/2.0 + oldRect.width()/2.0;
qreal y = pos().y() - boundingRect().height()/2.0 + oldRect.height()/2.0;
setPos(QPointF(x, y));
}
}
I am using QGraphicsTextItem to paint the text on the scene. Text is painted along the path (QGraphicsPathItem), wich is parent of my QGraphicsTextItem - so the text rotation is changed to be along the path element and is sticked to it while zooming the view. But the font size of QGraphicsTextItem is also changing while zooming the view - this is what I am trying to avoid. Of I set QGraphicsItem::ItemIgnoresTransformations flag to the QGraphicsTextItem it stops rotating while it's parent (QGraphicsPathItem) does.
I do understand that I have to re-implement QGraphicsTextItem::paint function, but I am stuck with the coordination system. Here is the code (Label class inherits public QGraphicsTextItem):
void Label::paint( QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget )
{
// Store current position and rotation
QPointF position = pos();
qreal angle = rotation();
// Store current transformation matrix
QTransform transform = painter->worldTransform();
// Reset painter transformation
painter->setTransform( QTransform() );
// Rotate painter to the stored angle
painter->rotate( angle );
// Draw the text
painter->drawText( mapToScene( position ), toPlainText() );
// Restore transformation matrix
painter->setTransform( transform );
}
The position (and rotation) of my text on the screen is unpredictable :(
What am I doing wrong? Thank you very much in advance.
I solved a problem this way - for drawing a line/circle/rectangle/path, which I want to be transformed, I use an appropriate QGraphicsLine/Ellipse/Rect/PathItem. For drawing the text (which I do NOT want to be transformed) I use QGraphicsSimpleTextItem. I set text's flag to ignore transormations and set it's parent to Line/Ellipse/Rect/Path item. The Line/Ellipse/Rect/Path item transforms, but text does not - this is what I wanted. I can also rotate text and set it's position.
Thank you very much for answers.
The following solution worked perfectly for me:
void MyDerivedQGraphicsItem::paint(QPainter *painter, const StyleOptionGraphicsItem *option, QWidget *widget)
{
double scaleValue = scale()/painter->transform().m11();
painter->save();
painter->scale(scaleValue, scaleValue);
painter->drawText(...);
painter->restore();
...
}
We can also multiply the scaleValue by other mesures we want to keep its size constant outside the save/restore environment.
QPointF ref(500, 500);
QPointF vector = scaleValue * QPointF(100, 100);
painter->drawLine(ref+vector, ref-vector);
I had this issue once. Instead of ignoring transformations, you need to scale down the items you don't want to be zoomed in in your zoom-in function.
When you zoom in, if you change the scale by ds for example, scale the items by 1.0 / ds
You might need to change their positions though.
I hope this helps.
Edit: I hope I understood the question right.