Ugh... Qt4 porting

Lars Knoll lars at
Mon May 16 16:03:42 BST 2005

On Monday 16 May 2005 16:47, Mosfet wrote:
> Lars wrote:
> >I did (just look at the mail header), but your mail server doesn't let my
> >mail through, and I'm honestly not willing to go through some stupid
> >registration process there.
> Strange that everyone else's mail to me including David's, Harri's, and
> Aaron's is coming in fine... Maybe they think you are spam ;-)
> > Yes, it needs second methods. If you have the right abstraction this
> > should not be terribly hard to do. Premultiplied alpha support is needed
> > if you want to get any decent speed when painting on QImages. The speed
> > difference when doing porter-duff operations (and almost all drawing is
> > that) on a non premultiplied and a premultiplied image is about a factor
> > of 4-6. That's enough for me to justify using the format.
> That's fine. If you read my emails I wasn't even really complaining about
> it at first. I was curious about it and asked where it was used.
> I took offense when first you stated it would not need modifications and
> then when wrong you started talking about how trivial it would be to
> reimplement the filters to use it natively. 

I said the math behind it is trivial. And yes, I do think that changing code 
to handle the premultiplied values instead of non premultiplied ones should 
in almost all cases be not too hard.

> This actually means three sets 
> of code for a lot of things: A palette source, RGB/ARGB, and premultiplied.
> All very similiar, but whatever. More likely I will only support RGB/ARGB
> at first and let developers know if they use a painter it will require
> conversion.

I would completely ignore paletted images for these things. Then you end up 
with two sets, and as I said with a little bit of abstraction, you will not 
duplicate a lot of code.


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