Mon Nov 29 21:15:38 CET 2004
John wrote:
So what's the problem with 3.7.5bx?
My experience is that the problem I've seen is in all vms I've used and 3.7.5b gives similar results to 3.7.4b.
Also I'm not sure what you mean by your comment that
earlier squeaks (image:? VM?) wouldn't recognize a 32bit screen depth?
That was an old recollection and impression I had from my early experiences with squeak. I just went back and tried some old vms with an old image and it did not seem to be true at least with 3.2.8b. Maybe I was mistaken.
I also tried to answer your questions by trying to find a way to pin things down.
With vm 3.7.5b classic and image 3.9a-6461 I did the following:
in a fresh project. Grab a ruler from objects. Made it 512@32 with grow handle With color properties set a ramp white-->black in direction 512@0.
Then I played with combinations of squeak screen depth from the appearance menu and hardware screen depth. from the apple control panel (actual the retractable tab version but you get the idea.)
When the squeak screen depth is set to 32 and the apple is set to thousands of colors the ruler showed 32 steps of gray. When the squeak screen depth was reduced to 16 the ramp appeared smooth no steps. When the squeak screen depth was put back to 32 and the apple set to millions of colors the ramp looked smooth.
When the screen depth now was reduced to 16 colors the ramp looked smooth.
I did grab patches on the various combinations and noticed some interesting things happened when I fooled around with squeak and apple screen depths. But there were some problems with reproducibility and analysis of the results.
The obvious work around is to have the screen depth and hardware depth match as often as possible.
While I believe there is a findable bug in all this (though maybe not in the vm) I don't think its a good thing for me to give a high priority to. If I stumble over something that illuminates it further I may get back to it. If not, not.
If I find something solid I'll post it on mantis.
Thanks for your response.
Yours in service --Jerome Peace
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Am 01.12.2004 um 06:40 schrieb Peace Jerome:
When the squeak screen depth is set to 32 and the apple is set to thousands of colors the ruler showed 32 steps of gray.
This is because "thousands" is 15 bits, that is 5 bits per component (red/green/blue), so 32=2^5 sounds about right.
When the squeak screen depth was reduced to 16 the ramp appeared smooth no steps.
This is because Squeak "dithers" gradients in 16 bit mode to make them look more smooth. Get a MagnifierMorph and look at the tiny patterns ...
When the squeak screen depth was put back to 32 and the apple set to millions of colors the ramp looked smooth.
As was expected.
When the screen depth now was reduced to 16 colors the ramp looked smooth.
Again, the dithering does a great job and the 16->32 bit conversion in the VM does no harm. Not anymore at least, VMs prior to 3.7.5 did this wrong (the gradient was distorted).
The obvious work around is to have the screen depth and hardware depth match as often as possible.
Well, 16 bits might be faster as there is only half the bits to be kicked around.
- Bert -
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