Graphics.drawRegion versus setClip and translate

[kruncher]

Hi guys,

I am scrolling a large image in a J2ME application on a regular Canvas, but have a question regarding performance and best practice.

In terms of readability and implementation, the g.translate and g.setClip approach is far simpler. But, will I notice significant (or even any) performance improvements with the g.drawRegion approach?

Many thanks,
Lea Hayes

[grahamhughes]

Hmmm... you might find that which performs better varies from device to device. For Nokias, I'd guess it would make no difference.

You might like to implement it both ways.

if (Device.USE_DRAWREGION) {
    // draw screen using drawRegion()
} else {
    // draw screen using setClip()/drawImage()
}

Then have a class like:

public class Device {
    public static final boolean USE_DRAWREGION = false;
}

You can have different versions of this class for different devices, kind of like having different .h files for a C program.

(Principle: when the expression in an "if" can be computed at compile time, because the values in it are either literal values or "static final", then the "if" is removed, and only the "true" code included in the compiler's output. This functions like conditional-compilation in C/C++ programs.)

Graham.

[kruncher]

Hi Graham,

I'll have to give it a try on some different phones. The clipping approach appears to work fine on my Nokia phone.

My concern was with the underlying API enumerating each pixel of the source image despite the clipping rectangle being considerably smaller.

Thanks for your advice, the macro-type approach may well be the way I need to go.

[grahamhughes]

My concern was with the underlying API enumerating each pixel of the source image despite the clipping rectangle being considerably smaller.

Painting through a clip region doesn't usually appear to be a problem. Most of the games I've worked on used setClip/drawImage in preference to drawRegion, since we usually wanted to support some MIDP-1 devices (drawRegion is new in MIDP-2). I have a feeling that some older Samsung devices (pre D500) might paint more slowly when painting through a clip region, but I never got time to validate this, and newer Samsung devices (D500 and later) perform much better.

I'm pretty sure you'll be safe either way, and I'd recommend doing whichever you're happy with. However, you can keep your options open easily enough.

You can read about several approaches to writing code for multiple devices in Java Porting in the wiki.

Graham.

[kruncher]

Thanks for the fantastic link, I hadn't realized how many different issues there were in terms of porting. I am going to spend some time reading through the different Wiki pages, there is a lot of interesting info there.