Quoting tim Rowledge <tim at rowledge.org>:

>
> On 08-02-2013, at 7:14 AM, Bob Arning <arning315 at comcast.net> wrote:
>
>> 15 is an empirical number from a long time ago. More rectangles can  
>> increase the number of times a given morph may be asked to draw in  
>> a single update cycle. Fewer rectangles increases the chances for a  
>> morph to be included when it hasn't changed itself. It's easy  
>> enough to change the 15 and to limit the clock display. It's also  
>> pretty easy to capture some data in  
>> PasteUpMorph>>privateOuterDisplayWorld to see what the effects are.  
>> Might be a big win or something less amazing.
>
> A plea here for letting the platform related code - ie the VM right  
> now, but damn well ought to be some platform bridges and policies in  
> the image - deal with assorted cost/benefits of number vs. size of  
> things like bitblts to the actual screen.
>
> On some machines it makes sense to do every little display-to-screen  
> right now because maybe there is a really fast GPU doohickey and it  
> costs no time at all. On others it might make sense to merge several  
> tiny  but widely spread regions into a single big one because the  
> memory bandwidth is good but the setup time is horrendous.
>
> There's way too much code buried in the system that tries to work  
> for all machines and all cases, often with no explanation why  
> certain strategies or values were used or what they mean, let alone  
> how changing things might work. There are poorly explained image  
> workarounds for vm problems, sometimes for only one platform or even  
> OS level. That leads to counter-work-arounds getting embedded in the  
> VM, with no good explanation for what is going on. Looking into the  
> sound system recently in order to get it going on the RISC OS Pi was  
> a horrible reminder of just how appalling some of this can get.
>
>
> tim
> --
> tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
> World Ends at Ten! Pictures at 11 on Fox News!
>
>
>
>

I fully agree with you.

In any case, in Cuis I redid the rectangle merge and update logic, and  
the result is much faster display redraws when there are many  
overlapping windows.

Cheers,
Juan Vuletich