Hi Jonathan,
If you can't use Java 2 APIs (introduced in version 1.2) then there are
going to be performance losses with having to deal with the ImageConsumer
and ImageProducer system, but there's not anything you can do about that.
(We created BufferedImages in 1.2 to facilitate the kinds of things that you
are trying to do.)
I'd say that 57,600 array accesses per refresh should be reasonably within
a good JIT's capabilities on any recent computer (say Pentium 3 or better).
It may be that with the overhead of the ImageSource having to feed the
pixels to the Image object that it pushes you over the edge. A couple of
things might be making different parts of this worse:
- What kind of ColorModel are you using? The default would be best if you
have int pixels and need alpha (which you presumably do to get the non-rect
image outline). The same ColorModel without alpha (i.e. the same red,
green, and blue masks) would be best if you can get away without alpha (i.e.
if you have a constant background color you could use).
- What does your inner loop look like? Maybe there are some inefficiencies
that are cropping up there. Many of the same rules of writing efficient
C code apply to Java as well, but there are some unique gotchas. Such as:
- Java requires array bounds checking on every array access so
try to use only one array load and store per inner loop:
// inefficient
dst[i] = r << redmask;
dst[i] += g << grnmask;
dst[i] += b << blmask;
// better
dst[i] = (r << redmask) + (g << grnmask) + (b << blmask);
(Work is being done in HotSpot to reduce array bounds checks,
but it isn't yet up to the task that image processing loops
tend to need and I don't know of any 1.1 JITs that did this.)
- Java has strict memory access requirements. If you use a
member field in the inner loop, copy it to a local variable
if you know it won't change (or if you want to protect yourself
from changes). This saves a field access per iteration.
Other tips and tricks may apply, but those are common pitfalls that I
can think of...
...jim
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