Reseting a mutable transparent image

[keithmarsh]

I have a mutable transparent image on a series 40 (4444 native pixel).
FYI I use it for a scrolling terrain buffer that's going to be drawn onto the screen over some background image.

I create the buffer using DirectUtils.createImage(w, h, 0x00000000) to set all the pixels to fully transparent.

Every frame I draw the terrain into my terrain image buffer and drawImage it over the background.


Now, I want to reset part of that terrain image to be fully transparent so I can draw some more stuff into it. I can't!
There appears to be no way to set a transparent image pixel back
to being 0x0000.

If I use drawPixel it leaves the original image intact.

So my question is:
------------------
Has anyone successfully reset a mutable transparent dirty image
back to being fully transparent?

Regards

Keith Marsh

[LongSteve]

Hi,

I think I understand your problem, but forgive me if I've got it wrong.

Obviously, you can't draw transparent pixels over the top of opaque pixels to create resultant transparent ones!

I presume you're trying drawPixels with transparency set to false?

It isn't documented exactly how DrawPixels works if you set the transparency flag to false. I suspect that it's overwriting the RGB data for each pixel, but leaving the Alpha component untouched, whereas you want it set to 0.

You'll have to do a getPixels on the image into an array of shorts, then loop over the array setting the pixels as you want them.

Bit of a bummer that, sorry. Have you tried it on a real phone at all? It wouldn't surprise me if the behaviour was different to the emulator.

Cheers,

Steve