I want to draw a HBITMAP onto HDC,
I used StretchDIBits. It works fine.
::StretchDIBits.
however, I only want a window to watch the drawing result, beside the window, I wish the stretchDIBits do not take any effect(It can not draw on other area), how can I do this?
When a child window is created, make sure the WS_CLIPSIBLINGS style is set to disallow painting outside the client area in WM_PAINT.
Other than that, SelectClipRegion is probably what you want.
Related
I am trying to make a simple program in which I have added a qgraphics scene and in this I have added a QGraphicsRectItem. I have implemented mouse press event, paint event, bounding rect. Now I have drawn a point on one side of rectangle because there can be multiple rectangle I can drop on screen so just to differentiate between them of different color. Now I can move my rectangle inside graphics seen and can increase the size of rectangle by moving it's one side at a time. The problem that I am facing is when I trying to draw point on one side of rectangle at the time of moving it, it leaves traces on graphics scene. can I remove the ghost lines?
This happens either because your boundingRect method isn't correct, or because you forgot to call prepareGeometryChange before making changes that affect the boundingRect result. Your boundingRect needs to include space for line widths, for example; that's a common mistake.
I'm using Qt's GraphicsView/GraphicsScene framework, and I have to draw some line items.
To be sure these items are always visible (independant of the zoom level) I use a cosmetic pen, with a size of 3 (for example) so I always get lines of 3 pixels width drawn on screen.
But these items doesn't receive mouse events (such as hoverEnterEvent/hoverLeaveEvent) when I'm zooming out a lot.
I've digged in the code, and it appears that all collisions tests are done with the return value of the shape() function.
So I've tried to re-implement "shape()" and also "contains()" and "collidesWithPath()" methods, but I still have problems to detect collisions (because when zoom is changed, I need to re-update the shape for example).
Is there any tricks to do that ?
In an efficient way ? (without re-updating the item's shape at every zoom change)
Thanks
I am able to paint a pixmap by using QPainter::drawPixmap, but I am having trouble with the sizing. The pixmap is being drawn onto many different scenes. Some of the scenes are very large, and some are very small. This results in the pixmap drawn being either looking very large or very small, depending on the size of the scene (or viewport, whatever its called). I need the pixmap to look the same size everytime, regardless of the dimensions of the scene it is being placed into.
Basically, I want it to work similar to drawPoint, where you can specify the length and width of the point in pixels, so the point looks the same size every time.
The following line of code is inside my paint function of the QGraphicsItem I subclassed:
painter_p->drawPixmap( pos(), MYPIXMAP );
with pos() returning the QPointF I need to draw the pixmap at.
Can't you use QGraphicsPixmapItem? It'd do exactly what you want.
I have an image that I show inside a canvas which I can zoom in on.
The problem is that when zoomed in, I try to drag the image, I can see the outline of the image in the foreground, (i.e.) outside the canvas boundary.
Is there anyway to tell the dragHandler to crop the "grabbed" image outside the canvas boundary?
In my experience using the built in drag/drop flex stuff is overkill for something that involves moving a component around in a canvas.
The easier way to do this (in my opinion) would be to listen for mouse down/up/move the image around in the canvas yourself.
When you detect a mouse down on your image, add a listener for mouse move (pro tip: make sure you set useCapture to true when calling addEventListener) and store the position of the mouse relative the origin of your image. Then whenever you get a mouse move, change the position of your image within your canvas taking into account the position of the mouse within the image (which you stored on mouse down). Keep doing this until mouse up occurs, then remove your mouse move listener.
There are some additional finer points to account for (what if the user drags outside of the canvas? Or outside of the browser window?), but this will get you started.
Hope that helps.
I'm working on an application where I'm drawing some rectangles on the screen, and then will need to manipulate the shapes (change their size, location). I tried to do something with .drawRect and clearing the shape each time I was manipulating it, but the RAM usage was spiking and then falling (presumeably because i keep reinitializing a new component and then removing it, and garbage collection was cleaning it out). This seems like its probably not the most efficient way to do it.
Is there a way for me to just create a shape once, and then move it around on a canvas (and change its width and height without all this RAM usage?
If all you're doing is changing it's offsets, and adjusting it's width and height without needing to fundamentally change the structure of the shape (such as rounding the corners of a rectangle of some such) you should be able to just maintain a reference to the Shape and adjust it's x, y, scaleX, scaleY properties to effect the changes.
You can try Degrafa to draw the rectangle.
To move the rectangle:
Changing the x and y or height and width property of the shape
Using the Flex Move Effect