Frame Buffer, DMA Question

[Johan]

[j.edwards]

[j.edwards]

Johan: That page about PocketHAL compared "flip times" between GAPI and PocketHAL...



1) Does GAPI mean GapiDraw?
2) Is "flip time" to flip between back buffer and front buffer?
3) Why does both GAPI and PocketHAL take so long on the iPaq, ie 17ms? I have an iPaq 1940 and can do it in 3ms etc and thought the 2210 was a few models up from mine.
4) You say an iPaq should be able to do it in 2.1ms, why doesn't that relate to any of the figures on that webpage?

The memory on the MediaQ is only 256kb which is enough to hold only 1 full screen display worth. How is it possible to have a backbuffer anywhere else but in normal ram?

PocketHAL says "Buffered access to the display. Blitting from the backbuffer to the frontbuffer is blazing fast."

However, to get data onto the backbuffer it would be just as slow as writing to the frontbuffer wouldn't it? In which case how is this an advantage if you have the additional overhead of having to copy from the backbuffer to the frontbuffer? Wouldn't it be better to build everything in ram then do one copy to the display memory?

PocketHAL says "Synchronization with the VSYNC signal to eliminate tearing (available for most devices)." - there must be a way to talk directly to the display ports as I mentioned in a previous post as this is the only way to get hands on VSYNC info. If PocketHAL can do that then it can also read the frame buffer address from the display io ports as well which explains why it doesn't need to rely on gx.dll.

Support for GDI surfaces is no worries...probably just using CreateDIBSection etc, but wonder how he can transpose to any other pixel format without speed loss.

Another thing...you have used speeds like "2.1ms" - how is it you measure in speeds less than 1ms? I am using GetTickCount().

[Johan]

[Kzinti]

[denthorq]

[j.edwards]

denthorg: You are right. I got a bit confused in my quest for answers. Apologies Thierry. Anyhow, not sure if wine is required anymore as I am starting to understand things and realise there is no point trying to redo everything Thierry has done with PocketHAL.

I have found it quite a learning curve though. A few weeks ago I began learning C++, and was therefore focused on speed to see just how well you could get things performing. I have found both the emulator and debugging on the iPaq really slow and tedious so am now building solely on the PC using MS VC++ using the same code in most cases, but with compatible classes for iPaq where there are differences - such as graphics - and occasionaly testing on iPaq. This has been going really well.

The game I am building is a RTS variant and I will publish it in the forums once a beta is ready. I also plan to publish code for some of the algorithms such as pathfinding and AI (for 2 not entirely unselfish reasons: because I've benefited hugely from other's sample code, and because there will no doubt be people who could help optimise them).

Must say, this is a really good developer community. Who actually runs the website?

[mlepage]

I do. BTW your first payment is due, I sent an invoice to your account. Also, no more flaming or I'll ban you.

[j.edwards]

mlepage: Are you just being smart? No idea what you're talking about. Care to explain?

[ppcStudios]

This forum's administrator is Johan Sanneblad, the originator of GapiDraw.

[mlepage]

Just a joke, I'm a bit ill today and likely exercising bad judgement. I should have added a smiley.

My understanding is that the site itself is run by a couple of individuals, and that others run individual forums. I believe it says at the top of each forum who moderates it.

[j.edwards]

mlepage: I was going to say! I mistakenly identified Thierry as Italian instead of French-Canadian - didn't realise the emotion such a "flame" could stir. :)

[mlepage]