When i move a QGraphicsItem, weird artifacts stay behind.Some parts of the item dont render,other render...
In the note.cpp i have a shape
QPainterPath Note::shape()const{
QPainterPath path;
// path.addRect(0, 0, 50, 20);
path.moveTo(0, -80.0);
path.lineTo(0.0, 80.0);
path.lineTo(80.0, 0.0);
// path.lineTo(75.0, -30.0);
path.closeSubpath();
return path;
}
In the paint function
QPointF *points = new QPointF[3];
points[0] = QPointF(0,-80);
points[1] = QPointF(0,80);
points[2] = QPointF(80,0);
painter->drawPolygon(points,3);
The first picture shows that all are fine when i start the app.
The second picture shows that when i move a triangle with the mouse, it gets sliced.Other times it leaves some trails and doesn't render all parts of the triangle
Here is the github link for the project.
Github link
To reproduce, just move a triangle.
QGraphicsItem for efficiency only repaint the section that returns boundingRect() method, in your case QRect(0, 0, 80, 80) only returns half the necessary area since the coordinate (0, -80) is outside the boundingRect. The solution is:
QRectF Note::boundingRect() const {
return QRectF(0, -80, 80, 160) ;
// or
// return shape().boundingRect();
}
Related
I'm trying to draw text inside a qgraphicswidget. The scale of the scene is -180 to 180 in the horizontal and -90 to +90 in the vertical (it's a world map).
When i zoom in to individual items on the map, i want some text to show up. My code for the paint function of one particular item looks like this:
void AirportGraphicsWidget::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget) {
QPen pen;
pen.setStyle(Qt::PenStyle::NoPen);
painter->setBrush(Qt::lightGray);
painter->setPen(pen);
if (m_curr_lod <= LevelOfDetail::MEDIUM) {
painter->setBrush(QColor(206, 211, 219));
painter->drawEllipse(m_airport_significance_rect);
} else if(m_curr_lod == LevelOfDetail::HIGH) {
painter->setBrush(QColor(56, 55, 52, 150));
painter->drawEllipse(m_airport_boundary);
DrawRunways(painter, option, widget);
} else {
painter->setBrush(QColor(56, 55, 52));
painter->drawEllipse(m_airport_boundary);
pen.setStyle(Qt::PenStyle::SolidLine);
pen.setColor(Qt::black);
painter->setPen(pen);
DrawRunways(painter, option, widget);
DrawILS(painter, option, widget);
DrawCOM(painter, option, widget);
QPen pen;
pen.setStyle(Qt::PenStyle::SolidLine);
pen.setColor(Qt::white);
pen.setWidth(0);
QFont font("Arial");
font.setPixelSize(15);
painter->setFont(font);
painter->setPen(pen);
painter->drawText(m_airport_boundary, "TEST");
}
}
The drawText call does not seem to be working at all. My scale at this zoom level is very small. The m_airport_boundary QRectF variable has the following values:
{ x = -0.010286252057250001, y = -0.010286252057250001, width = 0.020572504114500002, height = 0.020572504114500002 }
the drawing of the m_airport_boundary rect is visible so I know im trying to draw in the correct location. Can anyone tell me what I'm doing wrong?
Screenshot of what is drawing... The dark circle is the m_airport_boundary ellipse. Green things are a result of DrawILS and the blue circle is DrawCOM
The current QTransform scale is affecting the font size.
I suggest to calculate the text position in screen space, reset the transform and then call drawText().
Here is a snippet (suppose you want to draw at the center):
QPointF pos = m_airport_boundary.center();
QTransform t = painter->transform();
painter->resetTransform();
pos = t.map(pos);
painter->drawText(pos, "TEST");
How can I draw rounded line shape using QT. like this image.I need to design a rounded line when the button click.
void MainWindow::on_btnCreateRoundedLine_clicked()
{
}
Updated Image:
In this code which creates rectangle shape when the button click,likewise I need to create rounded line when the button click.And also which can able to rotate.
void Widget::on_btnCreateRect_clicked()
{
QBrush blueBrush(Qt::green);
QPen blackPen(Qt::black);
blackPen.setWidth(2);
rect = ui->graphicsView->scene()->addRect(-10,-10,250,100,blackPen);
rect->setFlag(QGraphicsItem::ItemIsMovable, true);
rect->setFlag(QGraphicsItem::ItemIsSelectable,true);
}
If you want to graph curves, a recommended option is to use QGraphicsPathItem, to that object you have to pass a QPainterPath:
QPainterPath path;
path.moveTo(10, 20);
path.lineTo(10, 40);
path.arcTo(QRectF(10, 20, 40, 40), 180, 180);
path.moveTo(50, 40);
path.lineTo(50, 20);
QPen redPen(Qt::red);
redPen.setWidth(2);
QGraphicsPathItem* item = ui->graphicsView->scene()->addPath(path, redPen);
/*
QGraphicsPathItem* item = new QGraphicsPathItem(path);
item->setPen(redPen);
*/
Output:
You can find a complete example in the following link.
I have the following code:
QGraphicsScene* pScene = new QGraphicsScene(this);
ui->graphicsView->setScene(pScene);
pScene->addRect(0, 0, 200, 200);
QGraphicsRectItem* pRect1 = pScene->addRect(40, 40, 100, 100);
QGraphicsRectItem* pRect2 = new QGraphicsRectItem(20, 20, 19, 19, pRect1);
QPointF pf1 = pRect1->pos();
QPointF pf2 = pRect2->pos();
QPointF pf3 = pRect2->mapFromParent(pRect1->pos());
QPointF pf4 = pRect2->mapToParent(pRect2->pos());
QPointF spf1 = pRect1->scenePos();
QPointF spf2 = pRect2->scenePos();
Nothing special, just a QGraphicsView with QGraphicsScene and a few QGraphicsRectItem(s).
Question: Why do all the points (pf1, pf2, pf3, pf4 and even spf1, spf2) equal QPointF(0.0, 0.0) after execution?
I'm using Qt 5.4.1.
From my understanding spf1 must be QPointF(40.0, 40.0) and spf2 must be QPointF(20.0, 20.0).
If you will look in the documentation then you will find:
QGraphicsRectItem *QGraphicsScene::addRect(const QRectF &rect, const
QPen &pen = QPen(), const QBrush &brush = QBrush())
Creates and adds a rectangle item to the scene, and returns the item
pointer. The geometry of the rectangle is defined by rect, and its pen
and brush are initialized to pen and brush. Note that the item's
geometry is provided in item coordinates, and its position is
initialized to (0, 0). For example, if a QRect(50, 50, 100, 100) is
added, its top-left corner will be at (50, 50) relative to the origin
in the items coordinate system
.As result, the coordinate of the Item is (0,0) but you can set it with:
pRect1->setPos(QPoint(30,30));
and look what will happen. Hope it will help you to understand QGraphicsScene coordinate system!
P.S.:
QGraphicsRectItem* pRect1 = pScene->addRect(0, 0, 100, 100);
QGraphicsRectItem* pRect2 = pScene->addRect(0, 0, 20, 20);
pRect1->setPos(QPoint(40,40));
pRect2->setPos(QPoint(20,20));
I need to position a top-level object so that it always remains in a position relative to another top-level object. As an example, the rectangle in the image below should stick to the "front" of the ellipse:
When rotated 180 degrees, it should look like this:
Instead, the position of the rectangle is incorrect:
Please run the example below (the use of QGraphicsScene is for demonstration purposes only, as the actual use case is in physics).
#include <QtWidgets>
class Scene : public QGraphicsScene
{
Q_OBJECT
public:
Scene()
{
mEllipse = addEllipse(0, 0, 25, 25);
mEllipse->setTransformOriginPoint(QPointF(12.5, 12.5));
QGraphicsLineItem *line = new QGraphicsLineItem(QLineF(0, 0, 0, -12.5), mEllipse);
line->setPos(12.5, 12.5);
mRect = addRect(0, 0, 10, 10);
mRect->setTransformOriginPoint(QPointF(5, 5));
line = new QGraphicsLineItem(QLineF(0, 0, 0, -5), mRect);
line->setPos(5, 5);
connect(&mTimer, SIGNAL(timeout()), this, SLOT(timeout()));
mTimer.start(5);
}
public slots:
void timeout()
{
mEllipse->setRotation(mEllipse->rotation() + 0.5);
QTransform t;
t.rotate(mEllipse->rotation());
qreal relativeX = mEllipse->boundingRect().width() / 2 - mRect->boundingRect().width() / 2;
qreal relativeY = -mRect->boundingRect().height();
mRect->setPos(mEllipse->pos() + t.map(QPointF(relativeX, relativeY)));
mRect->setRotation(mEllipse->rotation());
}
public:
QTimer mTimer;
QGraphicsEllipseItem *mEllipse;
QGraphicsRectItem *mRect;
};
int main(int argc, char** argv)
{
QApplication app(argc, argv);
QGraphicsView view;
view.setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
view.setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
view.setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform);
view.setScene(new Scene);
view.resize(200, 200);
view.show();
return app.exec();
}
#include "main.moc"
Note that the position of the rectangle is not always the same, but it should always remain in the same position relative to the ellipse. For example, it may start off in this position:
But it should stay in that relative position when rotated:
If you want the two objects to keep the same relative position, they need to rotate around the same origin point.
Here your circle rotates around its center (the point 12.5, 12.5), but your rectangle rotates around another origin (5,5) instead of the circle's center (12.5, 12.5).
If you fix the origin, it'll work as you expect:
mRect->setTransformOriginPoint(QPointF(12.5, 12.5));
Even if the rectangle starts off with an offset:
mRect = addRect(-10, 0, 10, 10); // Start 10 units to the left
I'm trying to make a Paint application in C++ with Qt. Everytime I click or click & drag the mouse, the program will draw something on a pixmap. After that, it updates the window calling paintEvent(), which will draw the pixmap onto the window.
void QPaintArea::mousePressEvent(QMouseEvent *event){
startpoint = event->pos();
drawPoint(startpoint);
is_pressed = true;
}
void QPaintArea::mouseReleaseEvent(QMouseEvent *event){
is_pressed = false;
}
void QPaintArea::mouseMoveEvent(QMouseEvent *event){
if(is_pressed == true){
endpoint = event->pos();
drawLine(startpoint, endpoint);
startpoint = endpoint;
}
else{
return;
}
}
void QPaintArea::paintEvent(QPaintEvent *event){
QDesktopWidget *desktop = QApplication::desktop();
int x = (desktop->width() - 800) / 2;
int y = (desktop->height() - 600) / 2;
QPainter painter(this);
QRect target(QPoint(x, y - 35), QSize(800, 600));
QRect dirtyrect(QPoint(0,0), QSize(800, 600));
painter.drawPixmap(target, *pixmap, dirtyrect);
}
The problem is that, the program is not printing the pixmap onto the window as expected. For example, I press the mouse at x: 17, y: 82 trying to draw something. The program will print what I drew but at an offset location, like x + 20, y.
Maybe I don't fully understand how QRect or drawPixmap works, but the pixmap is 800x600. "dirtyrect" is supposed to save the entire pixmap (starting a x: 0, y: 0, and the size 800x600).
drawPixmap(target, pixmap, source) paints on target rect of painter area (QPaintArea in this case) source part of pixmap. So you paint whole pixmap (0,0,800,600) at some (x,y-35,800,600) rect of QPaintArea. If you want to paint whole pixmap on whole QPaintArea just use drawPixmap(QPoint(0,0), *pixmap).
// EDIT
But if you expected, that pixmap will be painted with some offset from QPaintArea top left corner, then your calculations are wrong, and if you wont explain what did you want to achieve we won't be able to help you. Explain us your calculations of x,y (and magic -35 for y), and maybe we will be able to figure something out
// EDIT
You don't have to use window offsets like -35 if you're painting on widget. 0,0 of the widget is not top left corner of window frame, but of widget contents. How do you expect it to behave on other platforms?
If you want to paint it in the middle of your window simply use:
void QPaintArea::paintEvent(QPaintEvent *event){
QPoint middle = geometry.center();
int x = middle.x() - 800/2; // probably best would be pixmap->width()/2
int y = middle.y() - 600/2; // probably best would be pixmap->height()/2
QPainter painter(this);
painter.drawPixmap(QPoint(x,y), *pixmap);
}