Qt: how do I make a field of 2d-interpolated colors?

问题

I'm quite a beginner with c++, especially graphically related. I would like to make an animated background for my graphicsview which looks kind of like this:

Gradient Field Airflow

The picture represents the turbulence of an airflow over an object. The colors must be based on a matrix of values.

I can only find how to do single-direction gradients with QT.

How do I set this up? How do I get two-directional gradients?

/*edit It has been pointed out well that technically speaking this is not a gradient, but an color interpolation on a 2d array of nodes. */

回答1:

Well you have not provided the input data so no one knows what you really want to achieve !

if you have the flow trajectories and mass

Then you can use some particle system + heavy blurring/smoothing filtering to achieve this. For any known point along the trajectory plot a dithered circle with color depend on the mass/temp/velocity... and color scale. It should be solid in the middle and transparent on the edges. After rendering just blur/smooth the image few times and that should be it. The less points used the bigger the circles must be to cover the area nicely also can do it in multi pass and change the points coordinates randomly to improve randomness in the image...
if you have field strength/speed/temp or what ever grid values

Then it is similar to #1 also you can instead of particle system do the rendering via QUADs/Squares. The 2D linear gradient is called Bilinear Filtering
```
    c00   -- x -->  c01

      |
      |
      y      c(x,y)
      |
      |
      V

    c10              c11
```

where:

c00,c01,c10,c11 are corner colors
c(x,y) is color on x,y position inside square
x,y are in range <0,1> for simplicity (but you can use any with appropriate equations scaling)

Bilinear interpolation is 3x linear interpolation:

        c0=c(x,0)=c00+((c01-c00)*x)
        c1=c(x,1)=c10+((c11-c10)*x)
        c(x,y)   =c0 +((c1 -c0 )*y)

so render all pixels of the square with above computed colors and that is what you seek. This kind of filtering usually produce artifacts on the edges between squares or on diagonals to avoid that use non linear filtering or blur/smooth the final image

回答2:

There is a tutorial on gradients in Qt: http://qt-project.org/doc/qt-4.8/demos-gradients.html and a class: http://harmattan-dev.nokia.com/docs/library/html/qt4/qgradient.html I have never used other than linear gradients and according to the docs, it seems there are only three basic types of gradients available in Qt: linear, radial and conical. If you cannot compose your desired gradient using these three types, then I am afraid you will need to program your image pixels by yourself. Not to forget, it might be worthy to explore if OpenGL somehow could help. Qt has some classes using OpenGL but I am not familiar with them to provide more advice.

来源：https://stackoverflow.com/questions/20655174/qt-how-do-i-make-a-field-of-2d-interpolated-colors

标签

c++

colors

interpolation