Olivier DAVID wrote:
Phil,
What kind of algorithm did you use in software? I think a 90° rotate should
be something much easier than any rotation. I saw a piece of code in
xfree86, I hope it is optimised, but I didn't check it yet.
Nested loops, the obvious way. (No, I wasn't doing arbitrary-angle
rotation; just multiples of 90 degrees.) It could probably be
optimised a bit, but the fundamental problem is that you are passing a
lot of data through the CPU that would otherwise only go through the
graphics system.
Of course it all depends on your application: if all the data is going
through the CPU anyway then it won't make as much difference. In my
case, most of the content is either solid rectangles or blits from
cached images, so the graphics system is doing most of the work.
You might be able to estimate the slowdown: measure the bandwidth in
pixels/second to and from the framebuffer (being careful to allow for
the cache) and estimate how long a rotate will take from that. Then
add a sleep() somewhere in your program and see if it is still usable.
Maybe you will be lucky!
Regards,
Phil.
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