RE: Please review packaging of clanlib2

[Mark Page <rombust@hotmail.co.uk>]

My thoughts on ClanLib 2.3 Package with relation to SSE2 builds.


ClanLib main components are: (only including the ones relevant to this conversation)
  clanCore - (Contains SSE2 intrinsic that can be turned off by a #define)
  clanDisplay - (Contains SSE2 intrinsic that can be turned off by a #define)
  clanSound - (Contains SSE2 intrinsic that can be turned off by a #define)
  clanGL -  (Display Target: OpenGL 2.x and above)
  clanGL1 -  (Display Target: OpenGL 1.3)
  clanSWRender - (Display Target: Software renderer. Only supports SSE2 intrinsic)

 


Looking in detail at these components, disabling SSE2 would:
 clanCore and clanDisplay:  Gives only a very slight performance penalty. So we can ignore that
 clanSound: Runs at a slower speed.
 clanSWRender: This component is not available

 

For the average game without sound. This is not a problem.
For example, clanCore, clanDisplay with clanGL1 works nicely on the sparc platform (with minor fixes to some #includes)

 

All AMD64 builds should have SSE2 enabled. (Since AMD64 has always supported SSE2)

 

For the i386 platform the options are:
A) Disable SSE2 totally
B) Create 2 versions of the library ( something like /usr/lib and /usr/lib/sse2 - http://wiki.debian.org/Multiarch/LibraryPathOverview )
C) Enable GCC SSE2 only on the ".o" files that contain the SSE2 intrinsic. (The library chooses the correct code path at runtime)


Option A:
  clanSWRender is not available.
  There will not be any difference to games without sound running OpenGL.
  With sound, the speed difference depends on the CPU speed.

Option B:
  This adds extra complexity for little gain
  Application developers have to be aware that SSE2 may or may not be available
  A non-SSE2 clanSWRender would have to be implemented that throws a "not available" exception
  In the future ClanLib 2.4 may contains inline SSE2 intrinsic in the API. This might be an issue.

Option C:
  This requires someone changing the ClanLib source code tree
  Having a "if (sse2_enabled) func_sse() else func()" on matrix functions would have a performance penalty when called 10000's times.
  In the future ClanLib 2.4 may contains inline SSE2 intrinsic in the API. This might be an issue.
  Adds code complexity

 
So I think the simplest option is preferable. "Option A"

The work involved in using Option B and C, is not worth the effort. Also the ClanLib core developers may be reluctant to maintain it, since generally they work on Windows7 and have a minimum system specification)