Unstructured carpet plot

Hello everyone,
I am trying to show a scalar field through a carpet plot with carpet contours too. The grid is unstructured, this mean that some elements do not share some vertexes with the adjacent elements. Here is an example.

My problem is the following: each element of the domain is a carpet plot itself, therefore the interactive plot is really slow. I would like to plot the whole domain as a single carpet, but the arrays ‘a’ and ‘b’ (coordinates of the plot) should be different for each row and columns in order to represent the irregularity of the mesh. Is there a way to have such an unstructured subgrid within a single carpet?