Can I construct a color gradient in a rectangular region with given colors at the cornes in Qt?-CodePudding

I have a matrix of values of colours evenly spread across a grid with some pixels in between them. Something like this:

r _ _ g _ _ r ......
_ _ _ _ _ _ _ .....
_ _ _ _ _ _ _ ....
b _ _ r _ _ g ....
_ _ _ _ _ _ _ ....
_ _ _ _ _ _ _ ....
g _ _ b _ _ r ....
. . . . . . . ....
. . . . . . . ....
. . . . . . . .....

How can I construct/draw/paint a gradient with smooth transition in between colours in Qt C ? What tools should I use to achieve this?

I feel that somehow if I interpolate the colour values in the following rectangle, I can do it for the whole grid. -

   r
  _ _ 
g _ _ r
  _ _
   b

But the classes QLinearGradient, QRadialGradient, and QConicGradient seem to be of no use in this scenario as they take only two points as arguments.

CodePudding user response：

You can use bilinear interpolation to calculate colors between points in each cell:

for any given point h find colors e and f
where r, g, and b chanel of e is equal to   
r(e) = r(a)   (r(b) - r(a)) * distance(a,e) / distance(a,b)
g(e) = ...
b(e) = ...

r(f) = r(c)   (r(d) - r(c)) * distance(c,f) / distance(c,d)
g(f) = ...
b(f) = ...

and then find r(h),g(h) and b(h) interpolating between e and f vertically

r(h) = r(e)   (r(f) - r(e)) * distance(e,h) / distance(e,f)
g(h) = ...
b(h) = ...

a-e---b
| h   |
| |   |
| |   |
c-f---d