I am working on a qwtPlot and have implemented custom scrollbars to illustrate the position of things on the plot when zooming in (in regards to the whole thing - so basically the percentage).
Now, everything works fine, apart from the moment, when I do any zooming or panning right at the beginning (or simply when I see the whole plot and then I want to zoom in).
This is a slot I am using to refresh the appearance of the scrollbar:
void ScrollHorizontal::refreshAfterChanges() {
setValue(myPlot->getLowerBound(QwtPlot::xBottom));
setPageStep(myPlot->get_X_delta());
setSingleStep(myPlot->get_X_delta()/10);
setMaximum(myPlot->dataFromSources->lastTimeValMicro()-pageStep());
update();
printV("HorizontalScroll::setValue",myPlot->getLowerBound(QwtPlot::xBottom));
printV("value", value());
printV("pageStep", pageStep());
in the constructor I set the maximum to 0 (just in case, but it doesn't change anything)
The last 3 lines print out some values useful for debugging. What I found out thanks to them is that the slot is executed correctly, but the setValue(int) function doesn't work as I would expect it to:
//printed values right after starting the program
HorizontalScroll::setValue=0
value=0
pageStep=7320
//printed values after using the zoomer once
HorizontalScroll::setValue=956.316
value=0
pageStep=2225
Then, when I move the plot a tiny bit, e.g. zoom it 1.1 times, the setValue works properly and value() return the same thing I set. But if I go to the 100% view (the starting point) I get the same problems again.
Just to illustrate it, here are some screenshots:
http://tinypic.com/view.php?pic=2znph7s&s=8#.UvNkDoZhauY
(100% view, right before zooming in)
http://tinypic.com/view.php?pic=ke7nn9&s=8#.UvNkYIZhauY
(badly set qscrollbar)
Ok - problem was caused by the line
setMaximum(myPlot->dataFromSources->lastTimeValMicro()-pageStep());
It was setting the maximum to 0 sometimes. why? I wanted the slider to take up the whole length of the scrollbar so that at the beginning when the plot was shown in 100% view, you couldn't scroll it and I could achieve that by setting the pagestep to my plot's maximum value and the maximum to 0.
But that caused the setValue(int)problem - you can't set a value bigger than the maximum.
So what finally worked for me is:
double valueToSet=myPlot->getLowerBound(QwtPlot::xBottom);
if(valueToSet>maximum())
setMaximum(valueToSet);
setValue(myPlot->getLowerBound(QwtPlot::xBottom));
setPageStep(myPlot->get_X_delta());
setSingleStep(myPlot->get_X_delta()/10);
setMaximum(myPlot->dataFromSources->lastTimeValMicro()-pageStep());
update();
Related
I'm trying to make a subclass of QSlider that allows the user to insert "bookmarks" so they can remember significant locations on the slider. I've run into a problem painting the tabs on the slider - using QStyle.sliderPositionFromValue, I get a value but it is slightly inaccurate. If I'm on the left side of the slider, the tab is painted too far left, and on the right side it is painted too far right. I believe this is because QSlider.width() returns the width of the whole object, including the small offsets at the left and right. So width() might return 630 pixels, when the length of the slider itself is really 615.
This is the code I'm using to get the pixel position and draw a line across the slider.
pos = QStyle.sliderPositionFromValue(self.minimum(),self.maximum(),sliderIndex,self.width())
painter.drawLine(pos,0,pos,self.height())
I've been looking at the QT Source here starting on line 2699 and it seems like I need to be using the PixelMetric class from QStyle. I've tried using:
self.style().pixelMetric(QStyle.PM_SliderSpaceAvailable)
But that returns 0, which is clearly not the value I need.
I'd appreciate any advice.
Edit: As suggested in the comments, I changed the call to:
self.style().pixelMetric(QStyle.PM_SliderSpaceAvailable, QStyleOption(1,QStyleOption.SO_Slider),self)
This however, returns -14, which also doesn't match for the value of the offsets (I tried using self.width()-14 but the offset remains.
When using anti-aliasing rendering in Qt's QGraphicsScene, there is a behavior that makes drawings appear not as expected: overlapping lines become darker. I could not see any description of this behavior in the documentation, and I cannot find a way to disable it.
For example if I want to draw such a polygon:
Because of the number of points, it is impossible not to have overlapping lines - fine. But because anti-aliasing is activated, some borders appear 'thicker' than others.
Is there any way to avoid this and have anti-aliased lines that can overlap and yet at the same time be rendered without getting darker?
I know of course that I can redefine the paint() function and draw manually individual lines that do not overlap, but this is what I want to avoid. I am using Pyside and this would significantly slow down the application, due to the high frequency at which paint() is being called.
EDIT Fixed by defining the object shape using QPainterPath / QGraphicsPathItem instead of QPolygon / QGraphicsPolygonItem. In that case the moveTo function allows to avoid lines that overlap.
Another thing you could try is adding half a pixel to your coordinates (not dimensions). This fixed the anti-aliasing issue for me.
XCoord = int(XValue) + 0.5
YCoord = int(XValue) + 0.5
Also make sure that before that you have integer pixel values.
I'm working on a Qt based application (actually in PyQt but I don't think that's relevant here), part of which involves plotting a potentially continuous stream of data onto a graph in real time.
I've implemented this by creating a class derived from QWidget which buffers incoming data, and plots the graph every 30ms (by default). In __init__(), a QPixmap is created, and on every tick of a QTimer, (1) the graph is shifted to the left by the number of pixels that the new data will take up, (2) a rectangle painted in the space, (3) the points plotted, and (4) update() called on the widget, as follows (cut down):
# Amount of pixels to scroll
scroll=penw*len(points)
# The first point is not plotted now, so don't shift the graph for it
if (self.firstPoint()):
scroll-=1
p=QtGui.QPainter(pm)
# Brush setup would be here...
pm.scroll(0-scroll, 0, scroll, 0, pm.width()-scroll, pm.height())
p.drawRect(pm.width()-scroll, 0, scroll, pm.height())
# pen setup etc happens here...
offset=scroll
for point in points:
yValNew = self.graphHeight - (self.scalePoint(point))
# Skip first point
if (not(self.firstPoint())):
p.drawLine(pm.width()-offset-penw, self.yVal, pm.width()-offset, yValNew)
self.yVal = yValNew
offset-=penw
self.update()
Finally, the paintEvent simply draws the pixmap onto the widget:
p = QtGui.QPainter(self)
p.drawPixmap(0, 0, self.graphPixmap)
As far as I can see, this should work correctly, however, when data is received very fast (i.e. the entire graph is being plotted on each tick), and the widget is larger than a certain size (approx 700px), everything to the left of the 700px area lags considerably. This is perhaps best demonstrated in this video: http://dl.dropbox.com/u/1362366/keep/Graph_bug.swf.html (the video is a bit laggy due to the low frame rate, but the effect is visible)
Any ideas what could be causing this or things I could try?
Thanks.
I'm not 100% sure if this is the problem or not, but I thought I might make at least some contribution.
self.update() is an asynchronous call, which will cause a paint event at some point later when the main event loop is reached again. So it makes me wonder if your drawing is having problems because of the sync issue between when you are modifying your pixmap vs when its actually getting used in the paintEvent. Almost seems like what you would need for this exact code to work is a lock in your paintEvent, but thats pretty naughty sounding.
For a quick test, you might try forcing the event loop to flush right after your call to update:
self.update()
QtGui.QApplication.processEvents()
Not sure that will fix it, but its worth a try.
This actually might be a proper situation to be using repaint() and causing a direct paint event, since you are doing an "animation" using a controlled framerate: self.repaint()
I noticed a similar question to yours, by someone trying to graph a heart monitor in real time: http://qt-project.org/forums/viewthread/10677
Maybe you could try restructuring your code similar to that. Instead of splitting the painting into two stages, he is using a QLabel as the display widget, setting the pixmap into the QLabel, and painting the entire graph immediately instead of relying on calls to the widget.update()
I want to draw a tick mark for a qslider in paintEvent, so I should get the exact position of each tick mark. As you know, the handle of slider takes some space, so the first tick mark does not sit at the left/top position of the slider, there is offset of several pixels. Same thing happens to the last tick mark which indicates the maximum value. I want to know how many pixels of the space? (On win and mac, the handle are not in the same width)
If you have not yet done so, download the Qt source code and copy how they do it. You will want to look in the various Q...Style classes, i.e QMacStyle, QWindowsXPStyle, etc. Some of the key calculations come from:
QStyle::sliderPositionFromValue() method
QStyle::pixelMetric(QStyle::PM_SliderTickmarkOffset, ...)
Look in the various drawComplexControl methods for case CC_Slider:, where slider controls are drawn. In the Qt 4.7 code, this starts on line 2699 in qwindowsxpstyle.cpp, for example.
I have a problem with scaling an image in QT. I have a GraphicsView that has an image displayed and I have put in a slider to be able to allow the user to zoom in and out. For this, I've been using the scale function of the QTransform class to achieve this. It generally works if I zoom in, ie, if value gets bigger and bigger. However, when I go the opposite direction (making value smaller and smaller), the entire image disappears. Zooming back in doesn't fix the problem either; the entire image is no longer present no matter how much I zoom in or out. So the following are snippets of my code.
void MainWindow::on_ZoomSlider_valueChanged(int value)
{
QTransform transformer;
transformer.scale(scaler(value),scaler(value));
ui->graphicsView->setTransform(transformer);
}
qreal MainWindow::scaler(int value)
{
if(value < 0)
return 1/(-(value-1));
else if(value >0)
return value+1;
else
return value+1;
}
I'd be happy to offer any more clarification on my problem if it'd help you help me figure out what's wrong.
The 1/(-(value-1)) expression evaluates as an INTEGER, which is always zero in your case. Try using 1.0/(-(value-1)).
Also, I'm not really familiar with sliders, but I don't understand why could the value be negative. The valueChanged signal comes with the actual value, not the delta.