Re: [platform-swt-dev] GTK graphics status

[Mike_Wilson@xxxxxxx]

For comparison purposes, we re-coded the PNG image decoder code in C. On the particular benchmark we were running, the C code version took 2 seconds. The same benchmark run without the native (but with JIT enabled in the Java VM) took 3 seconds. So... The C code was faster, but not thrillingly so. Interestingly, if you run the Java code non-JIT, the time jumped to 36 seconds.

Note: I'm not claiming that code can't be made faster with natives, just that Java may not be as bad as you suspect.

McQ.

"Randy Hudson" <hudsonr@xxxxxxxxxx> Sent by: platform-swt-dev-admin@xxxxxxxxxxx 03/19/2002 02:09 PM Please respond to platform-swt-dev

To:        platform-swt-dev@xxxxxxxxxxx         cc:                 Subject:        Re: [platform-swt-dev] GTK graphics status

Scaling an Image should be fast.  Developers shouldn't be subject to a
10-100x performance hit because they are using Java.
If you are looping over every pixel, would you consider doing this in
natives?  I know the SWT philisophy, but I don't think the average
developer will benefit from stepping through such code in a Java debugger.



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  |       To:       platform-swt-dev@xxxxxxxxxxx                                                                                        |
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  |       Subject:  Re: [platform-swt-dev] GTK graphics status                                                                          |
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Silenio_Quarti@xxxxxxx writes:
> When a image has transparency (e.g. icons, gifs with transparent pixel),
> SWT creates
> a GdkPixmap for the color part of the image and a GdkBitmap for the mask.
>

I guess the hard bit is "Image implements Drawable" - otherwise you
could just implement Image as a pixbuf instead of a pixmap.

> We are using GdkPixBuf to scale the GdkPixmap. If we use a different
> algorithm to scale the GdkBitmap, we might have problems, since different
> algorithms might replicate different pixels.

Good point.

> So if we use our own algorithm the scale a GdkBitmap, I believe we will
> have to
> use it the scale its associated GdkPixmap too.

As you probably know that's a world of pain, since you have around 20
common GdkImage pixel formats to deal with, each in two possible byte
orders...

> Right now, we are getting a GdkPixBuf with alha channel from the
> GdkPixmap,
> getting the mask data using GdkImage, combining them by replacing the
> alpha
> channel with appropriate values (e.g. 1 -> 255, 0 -> 0), scaling the
> GdkPixBuf and
> then redering to the destination drawable by calling
> gdk_pixbuf_render_to_drawable_alpha.
>
> This is somewhat inneficient though.

Yeah it's pretty ugly, but I can't think of anything much better.  It
will be slow but not _that_ bad, as long as you don't do it on every
expose event or something.

There's a gdk_pixbuf_render_pixmap_and_mask() convenience function
too, FWIW, which you can use to generate a new pixmap/mask after
scaling the pixbuf.

Havoc
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