Problems with QwtPlotRenderer from Qwt 6

[mariposa]

The image has only 10% in size of the image I have created on my box with your parameters. Guess it gets scaled/compressed by the Forum software ?

Please recall that a QImage is simply a matrix of rgb values. If you want something scalable you need to use a scalable vector graphics format like PDF or SVG.

Yes, the size of the image is decreased by the forum software. But this doesn't matter with respect to the relative size of the plot elements. It is a fact that the axes/labels are getting smaller with increasing resolution. To proove it, I uploaded the original output image to an image hosting service:

http://img80.imageshack.us/img80/5470/bode300.jpg

I just changed line 216 of the mainwindow.cpp from the bode example and entered 300 dpi instead of 85 dpi. It is clearly visible that the axes are so small that they are barely visible if the whole image displayed on screen. Is this the desired behaviour of the function?

In an older version of my application I used the print() function and rendered the plot on a QImage. No matter how large the pixel size of the QImage was, the axes were rendered with the same relative dimension compared to the plot canvas. Meaning a picture of 300*200 pixels looked exactly the same as a picture of 3000*2000 pixels (of course extremely zoomed out to fit the screen). But of course the latter one had a higher resolution.

How can I achieve this result with the rendering implementation of Qwt 6? I just want the user to be able to export high-res pixel images.

The curve is fitted and painted using logical coordinates ( = screen resolution ) and translated to "physical" coordinates using painter transformations. Most ( all ? ) sizes in Qwt are in screen coordinates.

If you want to have the tolerance depending the target device resolution you could modify it according to the painter transformation f.e. at the beginning of an overloaded YourCurve::drawCurve().

Uwe

Many thanks for this hint, I will give it a try