My reimplemented QGraphicsItem draws a circle. It has flag ItemIgnoresTransformations, so it has always the same size when scaling. Should I set transformations manually for item's shape function to be accurate or there exists easy way? I need shape function for processing mouse events for this circle in QGraphicsScene.
Related
Let's say you have a resizable window with child scrollbar controls, and the scrollbars come and go depending on whether the window contents are large enough to require scrolling.
When both scrollbars are present, a small rectangle is effectively created in the bottom right corner of the window, at their intersection. Is there a clean strategy for clipping that rectangle when drawing on the window, so that you don't paint on it?
I guess my current approach is to obtain the rectangles for each scrollbar, and if those rectangles are not null, then use the rectangles' locations to determine the rectangle that we want to clip. And then call ExcludeClipRect for that rectangle. I guess a similar approach could be used, except with GetSystemMetrics(SM_CXVSCROLL) and GetSystemMetrics(SM_CYVSCROLL) to get the rectangle dimensions.
But is there a more accepted way of doing this, perhaps using some helpful clipping API functions? Thank you for any input.
I am trying to limit the movement of QGraphicsItem inside of a parent object inherited from QGraphicsPathItem that has an arbitrary complex shape (not square).
As I understand, I should extract each point of the moving object and check whether each of them is not contained in the parent QPainterPath. Then split the parent QPainterPath into small rectangle-shaped polygons and restrict movement area in the bounding box of each sub polygon.
So, I would like to know if there are any other options to exist. Thanks.
Maybe you can check on QGraphicsItem move event if it is still inside QGraphicsPathItem.
The check itself, you can do it with this QGraphicsItem method:
bool QGraphicsItem::collidesWithItem(const QGraphicsItem * other, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const
And to be sure that item is still fully enclosed inside its parent, set the mode to Qt::ContainsItemShape
If it is false, return QGraphicsItem to its previous position
EDIT: this check returns if QGraphicsItems shape is inside other QGraphicsItems shape, not its bounding box.
I am using Qt Graphics Framework for displaying an image. I have opened a raw image in subclassed QGraphicsScene in QGraphicsView using addPixmap(). I have added zoom feature by using scale function and drag mode is set as scroll hand drag. Now, I need to get the pixel coordinates within the scene on mouse hover such that the x and y value show the pixel in the image (drawn by pixmap) the mouse is currently pointing to. I tried using pos() but it didn't work.
Here is the code from Widget.cpp:
img = openImage(dirPath2.toLocal8Bit().data(),
sizeX,sizeY,file_heade,scan_heade,bpp,sign);
QPixmap x = QPixmap(sizeX,sizeY);
x.convertFromImage(img,Qt::AutoColor);
scene->addPixmap(x);
ui->disp_img->setDragMode(QGraphicsView::ScrollHandDrag);
GraphicsScene.h:
class GraphicsScene : public QGraphicsScene {
public:
GraphicsScene(QWidget *parent) : QGraphicsScene(parent){}
};
(preferably the pixmap coordinates but even that doesn't happen and if the values change when zoomed I will use scale factor to get the original values)
I suggest you start by reading about Qt's Graphics Coordinate System.
There are various layers of coordinate systems and you need to think about those with which you dealing with. At the top layer is the screen (or view), which is where the mouse coordinates reside.
The next layer from the view is the graphics scene. Graphics items, such as the QGraphicsPixmapItem which you added with addPixmap, reside here. The graphics scene can be visualised as a world of items, each with there own position and orientation.
Moving to the last coordinate system is an item's local coordinate system. If, for example, we take a rectangle, it may have local coordinates of (-5, -5, 10, 10) for (x, y, w, h). This item is then placed in the scene at some position. If its position is the origin of the scene (0,0), then the item's local coordinates would read the same as its scene coordinates.
However, if we move the rectangle +5 units in x-axis, its local coordinates are the same, but its scene coordinates would now be (0, -5, 10, 10).
Likewise, the view (QGraphicsScene) is a window into the scene and can be looking at the whole scene, or just part of it. As the view's top left coordinate is (0,0), it may map onto (0,0) of the scene, or may not, depending on what area of the scene the view is looking at.
So, by getting a mouse position you're starting in the view's coordinates and need to convert to the scene's coordinate system. Fortunately, Qt provides lots of useful functions for this at every level.
To convert the mouse coordinates from the view to the scene, you can use the view's mapToScene function.
Using the scene coordinates you can then get an item and map that to the local coordinate's of the item with the item's mapFromScene.
I inherited from the QGraphicsObject and created a new class that has a pixmap and sets its transform origin point to:
setTransformOriginPoint(boundingRect().center());
But when I call setRotation() on the my class (which is added to a QGraphicsView using the scene), the rotation doesn't use the center as the rotation anchor. How can I set the center to be the anchor of the rotation ? Thanks !
More information: calling setRotation() outside of a sceneEvent function it works, but inside a sceneEvent, upon a pinch gesture, the origin point doesn't work.
Draw pixmap at QRect(0, 0, pixmap.width(), pixmap.height(). Use this rectangle for bounding rect also. Use setPos to move the item around the scene. Use setTransformOriginPoint(pixmap.width() / 2, pixmap.height() / 2) to set the origin point. These coordinates are in the item coordinates, so they should point at the pixmap's center regardless of the item's position.
QT 4.7
I have a QGraphicsView / QGraphicsScene. The scene has a custom QGraphicsItem the whole scene is not displayed at one time, so it has a viewport.
I'm overriding the paint() method of my QGraphicsItem as follows:
void paint(QPainter *painter,
const QStyleOptionGraphicsItem *option,
QWidget *widget)
{
painter->setClipRect(option->exposedRect);
painter->save();
// Default identity matrix
QTransform transform;
// Apply some transform later
// The next line breaks stuff
painter->setTransform(transform);
// m_image is just a preloaded pixmap (i.e. watermark on all of these items).
painter->drawImage(QPoint(0,0), this->m_image);
painter->restore();
// Snip, do more drawing...
}
If I ever try to setTransform on the QPainter (i.e. if I'm trying to rotate the item), the view stops repainting the scene as a response to the horizontal or vertical scrollbars used to pan. The view also stops resizing the scene when I zoom in or zoom out.
The view will refresh if I resize the window or drag the window offscreen and then back onscreen. I've been looking over the QPainter Documentation as well as the examples and I can't quite figure out what I'm doing wrong. I'm assuming it's something to do with the coordinate system.
A guess:
The QPainter that comes to your paint method already has a transform on it that takes into account the viewport attributes (scale, rotation, etc.). When you call setTransform within your paint method you are blowing all that away. You probably want to perform a matrix operation on the existing transform rather than creating a new one.
Since you are calling setClipRect on your painter but then trying to paint under a completely different transform, you are painting outside your clip rect and nothing is happening.
It works when you resize or drag the window off screen because that forces a "redraw everything," so your clip rect includes your painting area in your alternate transform. Although I'm surprised it would appear in the correct location.