I have tested both 6.3 and 6.31 with your test, and the results are practically the same: 5422 fps for 6.3 and 309 fsp for 6.31.
17.54 times slower...
mIRC 6.3 took about 2 seconds to complete test, and mIRC 6.31 33 seconds.
I think that the diferences are different depending the system. In my core 2 duo are 17 times slower, but in a 1.6 ghz pentium M, the fps was 533 for 6.3 and 236 for 6.31. 2.2 times slower.
In Vista the diferences are minor too. In Vista the fps was 2475 for 6.3 and 1685 for 6.31. mIRC 6.3 is 50% slower in Vista respect XP, and 6.31 is the opposite, 5 times faster in Vista than XP (but always slower than 6.3 in XP and Vista). Curious.
In my example I used bitmaps from my pool game, the background is a bitmap of 450x248, and the sprites are the balls, 272x16.
I have tested the background in bmp and png format with the same result.
About PNG library, I think that mIRC, once time the bitmap, in every format, is loaded, cached and maped in RAM, the format doesn't matter, its a block of memory.
So, for me, mIRC 6.31 is 17 times slower in my core 2 duo, 2.2 times slower in mi Pentium mobile. In a medium 2 ghz pc perhaps is 2 or 3 times slower, a lot for a version with a few changes and bugs fixed.
