Hi Doug and others
I had been thinking about contour performance recently. I noticed a significant
fall in performance when I applied a transform to a large data set when using
the wxWidgets wxGraphicsContext driver on Windows - although I never
benchmarked it. This driver uses GDI+ for drawing, which isn't hardware
accelerated, not that it would matter much on my laptop.
I put the reduced performance down to changing from rectilinear coordinated to
non-rectilinear. Someone with better knowledge than me might correct me but I
guess that this means that the code calls a general polygon drawing function
requiring that for each quadrilateral generated by each set of four data points
the renderer has to iterate over every pixel in the image to check if that
pixel is inside the polygon. It may be that the renderer is cleverer than that
but there is still a cost to drawing non-rectilinear grids. Similar problems
are likely when the number of contours is so high that almost every rectangular
cell is cut by a colour transition. I wonder if plplot can be cleverer by
merging adjacent non-rectangular cells reducing the number of polygons drawn or
if it already does something like this?
Unfortunately I haven't got time to look further into this at the moment as I'm
working on some other wxWidgets driver things. I don't know if anyone else has
any thoughts?
Phil
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