Kommentare zu: How to write a KWin effect

Von: Hans Chen (mogger) 's status on Monday, 13-Jul-09 09:50:21 UTC - Identi.ca

Hans Chen (mogger) 's status on Monday, 13-Jul-09 09:50:21 UTC - Identi.ca — Mon, 13 Jul 2009 09:50:29 +0000

[...] http://blog.martin-graesslin.com/blog/2009/07/how-to-write-a-kwin-effect/ [...]

Von: andrew

andrew — Sun, 05 Jul 2009 11:16:37 +0000

Valid point about sending bytes to GL. Floats are less ambiguous and so always better to use if the library doesn’t just convert strainght back

Can I be so rude as to suggest code like the following for the XRender case:

const float alpha = 0.8f; // from top ... const int xr_alpha = 257 * alpha; // Note: 257*0xff = 0xffff col.red = unsigned short(xr_alpha * color.red()); // XRenderColor uses 16 bit color ...

May be overly pedantic but its how I think – sorry :-/
Anyway, thanks very much for posting a tutorial on this stuff. Very much appreciated.

Von: Martin

Martin — Sat, 04 Jul 2009 15:02:48 +0000

@andrew: yes using redF() would be better – I’ll change that. But I want to point out two points: first QColor stores the color value as an int and OpenGL uses floats. Sending an int to the graphics engine just will cause the same calculations and sending double – well that doesn’t improve anything. And given that qreal is mostly double kind of my logic is even better

Von: andrew

andrew — Sat, 04 Jul 2009 12:45:29 +0000

picky question… you use the code
glColor4f( color.red() / 255.0f, color.green() / 255.0f, color.blue() / 255.0f, alpha );

which exposes and hard codes colour precision for no clear reason (something I dislike) and involves implicit floatint conversion which has known performance issues on some platforms (see for example http://www.mega-nerd.com/FPcast/)… so I was just wondering:
1. Why not use glColor4b or
2. why not use redF(), greenF() etc. probably with glColour4d (as qreal is double for most platforms)

Later code also involves a lot of integer to float conversion also. Sorry – I’m not trying to be rude or a smart-arse. I guess I’m just suggesting that minimising the number of implicit casts going on would be good practice. Especially in example code that people are going to model their own code on.

Von: jospoortvliet

jospoortvliet — Fri, 03 Jul 2009 16:19:50 +0000

I put a link on techbase, but this should indeed get on techbase itself…

Von: Aaron Seigo

Aaron Seigo — Thu, 02 Jul 2009 19:29:19 +0000

this should totally be copy and pasted onto techbase in the tutorials section!

as for compiz, i agree that they’ve gone completely overboard with their configuration. great fun for tweaking, but impossible to use in real environments with regular joe’s.

contrast: kwin’s ability to easily select effects for things like window switching is elegant and actually passes the “my non-geek friends are able to use it” test

Von: Martin

Martin — Thu, 02 Jul 2009 14:01:32 +0000

@Mr Mister: please note that Compiz is not a GNOME application but an independent project. Personally I think Compiz offers too many configurations and even kwin offers too many (e.g. cube – that’s my fault). Where it makes sense we need configuration and where it does not make sense we don’t need and I’m hardly aware of anything that needs more configuration.

Btw: if you want a config option just report a wish on http://bugs.kde.org

Von: Mr Mister

Mr Mister — Thu, 02 Jul 2009 13:54:10 +0000

Maybe next a guide to how to write a proper configuration window/settings for the effect just created? Odd that KDE vs GNOME is always seen that GNOME is for small children and idiots whereas KDE stands for the tweak-everything-geeks but I can’t even adjust 10 % of the stuff in KWin that is there in Compiz.

Von: Tuukka

Tuukka — Thu, 02 Jul 2009 10:53:01 +0000

I’m very happy to hear you are making improvements to the resize effect! I actually submitted a wishlist bug a while ago about the very feature you describe (#182456). I hope the necessary API change will be made that the contents don’t have to be shown…

Oh, and thanks for the howto!