XAA vs. EXA in old hardware support

David D. Hagood wowbagger at sktc.net
Tue Jun 20 04:32:01 PDT 2006

Alan Cox wrote:
> That only helps for horizontal and vertical lines (and for older cards
> is generally slower there than writing to the frame buffer). Xtank is
> just a classic example of where hardware line draw should be used and
> why EXA should allow drivers to provide a line draw routine, at least
> for the non alpha case.

I'll give you a less frivolous, if also less common reason for fast line 
draws - instrumentation.

I design test equipment for a living 
http://www.aeroflex.com/products/commtest/pmrparametric/3900dr.cfm, all 
of which are X based). You put a oscilloscope drawing 500 line segments 
per trace, 2 live traces updating 20 times a second, a spectrum analyzer 
drawing a live trace at 500 lines per trace 20 times a second, an audio 
analyzer at 1024 lines per trace, 20 traces per second, and an I/Q plot 
at 1000 lines per trace at 10 traces per second, and YOU see how 
"unimportant" accelerated line draws are to you. (and yes, it is 
possible, and even common, for all 4 objects to be on screen at once.)

You kill fast line draws, you make X a hell of a lot less attractive for 
instrumentation guys like me. If I can hand a line segment to the 
hardware and let it draw while the CPU does something else that is a 

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