[haiku-appserver] Re: user needs to know about the clipping region?

  • From: "Rudolf" <drivers.be-hold@xxxxxxxxxxxx>
  • To: haiku-appserver@xxxxxxxxxxxxx
  • Date: Mon, 05 Dec 2005 22:26:14 +0100 CET

Ah, last time :)

ADI wrote:
>       There is a solution. Have you read what Rudolf said about allegro 
> game 
> library? AFAIRemember, it requires a frame buffer double the size of 
> screen. The driver gives it, but it only uses the first half to 
> display 
> on screen. Then there are 2 choices: 1) you draw in the 2nd part and 
> instruct the card to start retracing from it (swap buffers), then 
> draw 
> in the 1st part and swap again, and so on; 2) you could just use the 
> first part, prepare things in the 2nd, then blit using 2D HW with of 
> without transparency.
>       I'm not sure about this: but I think you can even request a frame 
> buffer 3 times the screen size.

My drivers support any size you want, as long as the hardware supports 
it. Even when only partial support exist: you will get it.
With this I mean: the acceleration engine has smaller constraints than 
the CRTC hardware. If your buffer gets too large the acceleration hooks 
nolonger get exported if you request them.

Although I implemented this, it's quite complex to be precise, and 
there's no means for you to know beforehand if you'll get acceleration. 
Therefore I am thinking I should remove non-accelerated support at some 

Note also: I do not advice to use allegro's trick. The large screen is 
meant to be used for a _virtual workspace_. If you alternatively use it 
to trick a double-buffer-whatever solution, you nolonger have the 
virtual workspace thing available (cleanly). Or things like the 
pageflipper demo.


Once more about overlay.
Axel's right: video overlays are not visibly transparant. Showing is 
determined by a specific color on the background. So you loose the 
modern cursor overlay's however _are_ (AFAIK). the RGB32 cursor is of 
course RGB24 with 8-bit alpha. RGB16 should be 1-bit alpha. Old cursors 
are still transparant: you preset one of the four colors to be 
transparant. Of course, this still means you only see the cursor image 
OR the background: no mix. Unlike RGB16/32 cursors. AFAIK.



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