Do I need WaitBlit before releasing image buffers?

PeterK · 09 September 2018, 21:15

I want to use BltBitMapRastPort() or BltMaskBitMapRastPort() and when these functions return I would like to release the bitmap plane buffers (the planar image) as soon as possible without wasting time.

Do I need to call WaitBlit() before using FreeMem() or is it guaranteed that the blitting is already finished when these two functions return?

Samurai_Crow · 09 September 2018, 21:33

I would imagine you would need to call WaitBlit() because the allocation scheme would have no knowledge of custom chip usage and could end up with a race condition between the blitter and CPU.

mark_k · 09 September 2018, 21:48

Yes, the RKM says:
"The graphics library rendering and data movement routines generally wait to get access to the blitter, start their blit, and then exit without waiting for the blit to finish. Therefore, you must WaitBlit() after a graphics rendering or data movement call if you intend to immediately deallocate, examine, or perform order-dependent processor operations on the memory used in the call."

PeterK · 09 September 2018, 22:22

Many thanks, that's exactly what I wanted to know. So I better keep the WaitBlit() in my code.

09 September 2018, 21:15	#1
PeterK Registered User Join Date: Apr 2005 Location: digital hell, Germany, after 1984, but worse Posts: 3,365	Do I need WaitBlit before releasing image buffers? I want to use BltBitMapRastPort() or BltMaskBitMapRastPort() and when these functions return I would like to release the bitmap plane buffers (the planar image) as soon as possible without wasting time. Do I need to call WaitBlit() before using FreeMem() or is it guaranteed that the blitting is already finished when these two functions return?

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09 September 2018, 21:33	#2
Samurai_Crow Total Chaos forever! Join Date: Aug 2007 Location: Waterville, MN, USA Age: 49 Posts: 2,186	I would imagine you would need to call WaitBlit() because the allocation scheme would have no knowledge of custom chip usage and could end up with a race condition between the blitter and CPU.

09 September 2018, 21:48	#3
mark_k Registered User Join Date: Aug 2004 Location: Posts: 3,335	Yes, the RKM says: "The graphics library rendering and data movement routines generally wait to get access to the blitter, start their blit, and then exit without waiting for the blit to finish. Therefore, you must WaitBlit() after a graphics rendering or data movement call if you intend to immediately deallocate, examine, or perform order-dependent processor operations on the memory used in the call."

09 September 2018, 22:22	#4
PeterK Registered User Join Date: Apr 2005 Location: digital hell, Germany, after 1984, but worse Posts: 3,365	Many thanks, that's exactly what I wanted to know. So I better keep the WaitBlit() in my code.

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