I have a problem while scaling and transforming QGraphicsPixmapItem. I have created graphics editor in which I am using QGraphicsItem of initial size 100,100 and after that I am resizing and rotating it by setTransform() method.
After that I am storing this transform and using these for my another application called player in which I am using those transform and showing images and videos on it, I am using QgraphicsPixmapItem to show images now if I set scaled and setTransform methods to image its clarity gets spoiled.
Is it possible to keep clarity as it is even if I scaled and transform it.The image I am using is of 2560x1440 pixels.
Any help will be appreciated.
The code is :
QGraphicsPixmapItem *pixitem = new QGraphicsPixmapItem;
pixitem->setFlags(QGraphicsItem::ItemIsMovable);
pixitem->setPos(50,50);
QTransform trans;
trans.setMatrix(4.20399,2.9286,0,-3.86601,0.761397,0,33.1015,-134.5,1);
pixitem->setPixmap(QPixmap("abc.jpg").scaled(100,100));
pixitem->setTransform(trans);
pixitem->setShapeMode(QGraphicsPixmapItem::MaskShape);
scene->addItem(pixitem);
You can use setTransformationMode function to set the pixmap item's transformation mode. The default value is Qt::FastTransformation. You should set the transform mode to Qt::SmoothTransformation to enable bilinear filtering which results in a better quality when scaled :
pixitem->setTransformationMode(Qt::SmoothTransformation);
Related
I use QtQuickControls 2 together with QQuickItem-derived class in my app. After I set AA_EnableHighDpiScaling attribute and all QQuickControls 2 components look correctly on my smartphone but object of my custom class is scaled incorrectly. Here is the app without HighDpi scaling with minimum zoom(the way it is meant to work):
And here is the one with scaling with minimum zoom:
It seems that on the second screen the object is scaled too much and I can see square pixels of all textures that I draw with QPixmap or QImage. However, the images that I load from external memory and nodes like QSGGeometryNode look correct. Can I switch off scaling for just one particular QQuickItem? If no, what should I set to render it correctly?
Also, when I try to set opacity on QQuickItem with a lot of QSGOpacityNodes in scene graph node tree I get segmentation fault. What can cause this?
So I solved this problem by dividing the size of QSGTexture by QQuickWindow::effectiveDevicePixelRatio() and also multiplying the size of the image from which texture is created by this ratio.
If you are drawing the text using on QImage you should also multiply your font's size by this ratio. The same thing should be done with geometrical shapes and QPixmap::scaled().
I am trying to rotate am image around its origin(center) in QT using QWidgts in C++. I experimented a lot of things here, but no matter what I do, the image keeps rotating around some arbitrary position I have no clue of. Kindly, help me out here. I am new to QT.
void gaugeWithRedZoneImage::rotate()
{
QPixmap pixmap(*gaugeMainScreen->pixmap());
QMatrix rm;
rm.translate(0, 0);
rm.rotate(-360);
pixmap = pixmap.transformed(rm);
gaugeMainScreen->setPixmap(pixmap);
/*QTransform rotate_disc;
rotate_disc.translate(pixmap.width()/2.0 , pixmap.height()/2.0);
rotate_disc.rotate(-60);
rotate_disc.translate(-(pixmap.width()/2.0) , -(pixmap.height()/2.0));
pixmap = pixmap.transformed(rotate_disc);
gaugeMainScreen->setPixmap(pixmap);*/
}
Form the documentation of QPixmap::transformed():
The transformation transform is internally adjusted to compensate for unwanted translation; i.e. the pixmap produced is the smallest pixmap that contains all the transformed points of the original pixmap.
This means that the method ensures no clipping takes place by appending the canvas. No matter what your rotation center was, the automatic extension of canvas will almost always result in a perceived shift.
Image examples might help to further diagnose the problem.
As ypnos said, your problem isn't the rotation center. When you rotate your image, its width and height will most likely change and no longer fit your container (gaugeMainScreen) dimensions.
You have some possibilities to overcome this problem. One of them is to set your container to scale its contents (you can use the method setScaledContents()). In this case, you have to keep the original image around and use it whenever you apply a rotation, otherwise your image will appear increasingly smaller.
I am new to Qt. I am representing events from my application as polygons in my scene, using a custom class that inherits QGraphicsPolygomItem. The polygon dimensions are (event duration, fixed height), using 1s : 1px. Event duration can be as low as 1E-6, so I simply scale my view so that the smaller polygon is scaled up to MIN_POLY_WIDTH (10px):
view->scale(qreal(MIN_POLY_WIDTH/min_event_duration), qreal(1.0));
So far so good. However, I have a QGraphicsTextItem child for each polygon, which get stretched by the scale operation to a point they get way outside the polygon boundaries:
The text item is created as follows:
void EventPolygon::setId(QString id) {
if (!this->id) {
this->id = new QGraphicsTextItem(id, this);
} else {
this->id->setPlainText(id);
}
this->id->setPos(0, this->polygon().boundingRect().height() / 2 - this->id->boundingRect().height() / 2);
}
That function is usually called by EventPolygon constructor. I though that was the issue, since scale is done after all items are added to the scene, so it would affect the text items. So I tried calling setId after the scale operation, by iterating over all items in the scene. That way I though only the polygons would be stretched. That was not the case, and the text remained stretched.
I also tried using the following instead of scale:
QTransform t = QTransform();
t.scale(qreal(MIN_POLY_WIDTH/min_event_duration), qreal(1.0));
view->setTransform(t, false);
I thought "false" would avoid the transformation being applied to the polygons children, however it seems that is not the case. Is there any way I can scale the polygons to 10px width min and have a readable text inside them?
The QGraphicsScene forms a scenegraph hierarchy based upon the parent-child relationships, transformations are inherited down this hierarchy - there is no way round this (see the Transformations section here).
So to fix your issue, you will need to make the child QGraphicsTextItem invert the scaling transformation of the parent multiplied by the scaling of your view.
In fact I really recommend that you never set view transformations that are not for simulating a camera operation (pan, zoom, etc.) for this reason. I would simply allow for the seconds per pixel ratio to vary and allow the child items to be able to query this from the view - in other words have the progress items take care of their own size on screen.
That was not the case, and the text remained stretched.
Changing the transformation stack will cause a redraw, that's why it doesn't matter when you set the scale.
I thought "false" would avoid the transformation being applied to the
polygons children
No, the combine argument when false just overrides the existing transformation matrix with the one you are providing.
I am writing a GUI application that works on Mac and Win and there is one little problem, which i do not know how to solve.
In my application I have a small (250 x 250 px) preview window (let' call it SW) in which placed the image. Image can be much bigger, than SW. Somewhere I have a slider which implements zoom function of image inside SW. My main problem is implement zoom function on this image.
On enter I have:
source image and it's width and height;
view image - it is zoomed copy of source image;
position of zoomed image
size of viewport is 250 x 250 px
It should works like zoom in image processing programs. When we changing our zoom value image becomes smaller or bigger relative to viewport center and position of image inside it. We can move image inside of viewport.
For correct implementation of that problem we need to calculate images size and position inside our view. I'm already wrote some "algo" that implements image size modification.
It is looks like:
float one = (source_original_size - thumbnail_size) / 100;
int bigger_side_size = qRound((100-value) * one) + thumbnail_size;
But I can not imagine how I can calculate position on scene of that zoomed image.
Can anybody help me with ideas?
If it is important I am using Qt framework and QGraphicsView, QGraphicsScene and QGraphicsPixmapItem.
Take a look at the Image Viewer Example, it has some features that you are looking for.
Hi i want to develop game like 'Doodle jump'.But i have some problem with the following features-
1.How to move background scene/image.
2.How to detect collision between object.Is it needed a physics engine like box2d or i should just use manual collision.
3.what should be the size of the background image.
4.In fact i have no idea how does background move .So i need a explanation from someone.
Background Movement
A) You could create a TMX Tilemap and then make a very high Tiled-Map.
B) You could create one texture and then cycle the texture coords instead of really moving it.
Detect it manually. Best is detect it via "Point in Boundingbox" or "Rect in Rect".
For more detail visit my blog entry for collision detection with cocos2d : http://www.anima-entertainment.de/?p=262
Size of an Image
Keep in Mind that textures are always at power of 2 in the memory. If you want to create one Background-Image at retina highresolution (960x640 Pixel) in the memory will be a texture of 1024x1024. If possible use smaller Background-Images and stretch them. (like 512x512). But I really would recommend for big scrolling images the TMX Support.
CCTMXTiledMap * tmxNode = [CCTMXTiledMap tiledMapWithGMXFile:#"Level.tmx"];
// lets say you want to move it 50 pixels down in 1 second :
[tmxNode runAction:[CCMoveBy actionWithDuration:1.0 position:ccp(0,-50)];
To create a tilemap : http://www.mapeditor.org/
In the folder of cocos2d, you could get many demos of tilemap.
TileMapTest.h
TileMapTest.m
refer this tutorial this will helpful for you.
http://www.raywenderlich.com/2343/how-to-drag-and-drop-sprites-with-cocos2d
this is used screen movement with pan recognizer