There is a Theme system setting variable...but...

[cyrille de brébisson]

Hello,

Prime came after the 39GII+ which was extremly memory limited (<256KB). So when we started the prime development, we were in a "memory is rare" mind set. Add to this the fact that we did not know when we started how large the Prime memory was going to be and you will understand the decision of using the RGB555 format.

RGB555 is, in lots of ways, slower than 888 because it requires more computations as soon as alpha blending comes in (which is very frequent). Prety much the only time where 555 is faster is when there is a pure erase as pixels can be erased 2 at a time.

Windows does support 555 blitting on a window, so it was not an issue.

However, most other OS do not support 555 color schemes, especially handhelds, which meant expensive (power wise) conversions all the time as the screen was refresh. QT (which we now use on PC and MAC) does not support 555 either.

Add to this the fact that we have reclaimed a lot of memory in Prime and you will understand why we are switching to 888.


About sprites and the like. Remember that we have also added jpg and png support to the system. Although I have not tested it with 4 bpp, you will be surprised to see that png (the most appropriate in this case), will compress a 16 color sprite encoded in 888 just as well as it will compress the same picture encoded in 4bpp (which is normal). So there is little extra cost in using 888 here.
The only cost is in the memory used when the program is actually running and that the decoded graphic is in RAM. But then, you want speed and 888 to 888 blits go faster than 4 to 888...

Cyrille