[prev in list] [next in list] [prev in thread] [next in thread] 

List:       xfree-render
Subject:    Re: [Render] Point sampling trapezoid alpha (was: Another subtle issue...)
From:       Keith Packard <keithp () keithp ! com>
Date:       2002-12-19 18:46:36
[Download RAW message or body]


Around 21 o'clock on Dec 19, Vadim Plessky wrote:

> I am wondering: do you assume 	that d (alpha depth) is integer?
> IIRC, alpha is float in Xr.

We're discussing the Render extension here which uses integer alpha values
formed from an integer number of bits.

> I am also wondering how your algorithm would work with 1x1 rectangles 
> ("trapezoids"), and other small in size trapezoids (1x2, 2x2, 2x2).
> Do you plan to have some kind of exceptions for those sizes?

Any full-pixel sized objects have unambiguous definitions under any alpha 
computation mechanism.

> Do you make some assumptions of sub-pixel geometry here, or that *geometry* 
> can be *tuned*, in some way, in the future?

We're talking about the Render fixed point coordinate space here which 
uses 16 integer and 16 fractional bits.  There is no mapping from that 
coordinate space to the "sub-pixel" geometry of an LCD screen.

Keith Packard        XFree86 Core Team        HP Cambridge Research Lab


_______________________________________________
Render mailing list
Render@XFree86.Org
http://XFree86.Org/mailman/listinfo/render
[prev in list] [next in list] [prev in thread] [next in thread]