Re: [9fans] Double buffering graphics

Re: [9fans] Double buffering graphics

[andrey mirtchovski]

> Any pointers on how I can implement
> double buffering graphics in  Plan9 ?

if you want an example of double buffered graphics in p9 you can look
at the XaoS source (http://www.acl.lanl.gov/plan9/xaos the relevant
file is in ./src/ui/ui-drv/plan9/).

it uses a single Image and two pixel arrays.  it works on the current
array and when it's ready executes a loadimage() and a draw()

pretty similar to Russ' solution

Re: [9fans] Double buffering graphics

[Douglas A. Gwyn]

> > Be sure to switch during the vertical retrace interval,
> > to avoid yucky visual artifacts.
andrey mirtchovski wrote:
> who should take care of that?  the drawing library (i.e.  draw()), the
> software or the driver?

If you're really fortunate, the graphics hardware was designed to
help in this frame synchronization.  Just how you do it depends on
the graphics subsystem (software and hardware) architecture and
capabilities.  As to who "should" take care of it, it "should" be
whoever is in the best position to detect the VRI onset, perhaps
an interrupt handler (which would simply switch buffer pointers).

Re: [9fans] Double buffering graphics

[Douglas A. Gwyn]

rsc@plan9.bell-labs.com wrote:
> One cheap way to do double buffering
> is to just allocate two images and then
> draw them onto the screen alternating
> between them.

Be sure to switch during the vertical retrace interval,
to avoid yucky visual artifacts.

Re: [9fans] Double buffering graphics

[andrey mirtchovski]

> Be sure to switch during the vertical retrace interval,
> to avoid yucky visual artifacts.

who should take care of that?  the drawing library (i.e.  draw()), the
software or the driver?

Re: [9fans] Double buffering graphics

[rog]

> Writes from normal memory to video memory
> are very fast.  The reverse operation is very slow
> (I've seen faster 5400rpm disks).

is it this that causes the big slowdown when
part of a window is off screen?

Re: [9fans] Double buffering graphics

[rsc]

yes.  then every operation is implemented by
copying the visible part of the window to the
main memory copy, performing the operation
there, and copying the visible part back.

russ

Re: [9fans] Double buffering graphics

[rsc]

That depends on exactly what you are trying to
accomplish.

If you want double buffering in the video
memory itself, that will take some work
(like a video memory allocator).

One cheap way to do double buffering
is to just allocate two images and then
draw them onto the screen alternating
between them.

If all you want is for the user not to see
intermediate images, you could just allocate
one image, work there, and draw it to the screen
whenever it is presentable.

Writes from normal memory to video memory
are very fast.  The reverse operation is very slow
(I've seen faster 5400rpm disks).

Russ

[9fans] Double buffering graphics

[Elizabeth Strumph]

Hallo,

Any pointers on how I can implement
double buffering graphics in  Plan9 ?

Thanks much
--Elizabeth

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