[PD] pd, tcl/tk, the gui, quartz and you

[chris clepper]

I did a little test to figure out why updating the pd gui causes so 
much CPU activity on OSX.  The test consists of four groups of metro, 
random, and some number boxes placed around the patcher window.  To 
run the test, you need to run the patch and a little app called 
Quartz Debug, which is part of the Developer Tools (it's in 
/Developer/Applications/).  This fantastic tool shows which parts of 
the screen are updated by flashing the area as a colored box.

In the Quartz Debug window, check the box next to 'Flash identical 
updates' for this test.  Open the patch and start the first number 
box in the upper left spinning - you will see the number box flashing 
red as it updates.  Now stop that one and go to the middle set of 
objects and start the metro - notice that there is a red rectangle 
connecting the two number boxes as they update.  Next go to the 
objects in the upper right and repeat the test - don't do this if you 
are epileptic!!  At this point, you might be thinking, it's the patch 
cord connecting them that's the problem.  Well start the metro in the 
top left and the bottom right and witness the wrath of Quartz Debug! 
Run the tests again with top open and see how much CPU is being 
drained.

Ok what does the red box and the test really mean?  It shows that 
there is a huge amount of wasted cycles updating part of the gui that 
doesn't need updating.  I don't really know where this inefficiency 
comes from - it could be tcl/tk* or the way pd uses tcl/tk or ???. 
Maybe someone with more knowledge can have a look into this, and 
figure out what's going on, or at least give me a hint where to look.

*My suspicion is that it's tcl/tk at fault here.  Incidentally, the 
WishShell spends most of it's time converting RGB pixels to ARGB 
while the huge red rects are being updated.  Seems truly wasteful.

cgc