a few questions about using QwtMatrixRasterData (and other classes)

[Uwe]

I have 4 colors. in my case it's very necessary to have only clear colors without smooth gradient between each color.
can I achieve it with this component? and how... may be try another alternative?

How to map values to colors is the job of the color map. You can write your own one, but I guess setting QwtLinearColorMap::FixedColors mode is all what needs to be done.

hereby we have coordinates in the hint near cursor (x, y)
how to add here the third value of z axis?

pos is the position in plot coordinates. All you need to do is to ask the matrix raster data object for the z value at the position.

How to disable zooming out below a certain value (for example when the pic fit to width)?

Depends on how you have implemented zooming.

F.e. QwtPlotZoomer never zooms out of the initial scale ranges, that have been set by the application. Here the answer would be simply: don't assign scale ranges you don't want to have.

Uwe