QwtPlotSpectrogram and QwtRasterData

[Uwe]

x/y are values from the scales. How your values are related to the scale coordinates is something I can't tell you.

The implementation of "value()" you have posted will be way to slow. It will be called for each pixel of the canvas ( when there is no pixelHint() ). You can't have an operation like indexOf() there.

Also indexOf() will fail for almost all values as the position of the pixels usually never meet the position, where you have a value. So you usually have a to do something called resampling. Mostly it is a nearest neighbor algorithm, but you might use some sort of interpolation as well.

F.e. QwtMatrixRasterData offers nearest neighbor and bilinear interpolation.

Uwe

PS: If all you want to do is to map values at a specific position to a colored dot QwtPlotSpectroCurve might be what you are looking for.

[jesse_mark]

QwtPlotSpectroCurve was close to what I want to do, but as I have too many points QwtPlotSpectroCurve is a bit slow when zooming or when dropping it after panning.

about QwtMatrixRasterData, so to use it we just assign a matrix of values to it.
how does it assign these values to the points ???
what is the affect of number of columns ??
other thing is as a I have -1 means no color, I tried the addColorStop(-1,qRgba(0,0,0,0)) but the colors still show even with QwtPlotSpectroCurve.


Thanks