On Mon, 2010-01-18 at 12:26 +0100, ext Y, Kishore wrote: > > -----Original Message----- > > From: Tomi Valkeinen [mailto:tomi.valkeinen@xxxxxxxxx] > > Sent: Friday, January 15, 2010 4:00 PM > > To: Y, Kishore > > Cc: linux-omap@xxxxxxxxxxxxxxx > > Subject: Re: [PATCH] OMAP3630:DSS2:Enable Pre-Multiplied Alpha Support > > > > Hi, > > > > On Mon, 2009-12-21 at 16:06 +0100, ext Y, Kishore wrote: > > > From 2f873819a4b9eb0bd658db1e59408d8f0aeb14b6 Mon Sep 17 00:00:00 2001 > > > From: Sudeep Basavaraj <sudeep.basavaraj@xxxxxx> > > > Date: Mon, 14 Dec 2009 18:54:51 +0530 > > > Subject: [PATCH] OMAP3630:DSS2:Enable Pre-Multiplied Alpha Support > > > > > > Enables dss to process color formats with pre-mulitplied alpha values. > > > With this we can have alpha values defined for each pixel > > > and hence can have different blending values for each pixel. > > > > What does pre-multiplied alpha mean? The TRM didn't really open it up... > > Don't we already have per pixel alpha when using ARGB/RGBA? > > When we set pixel format to ARGB/RGBA dss alpha blender would multiply the value present in 'A' with 'RGB'. > By setting this bit display hardware assumes that the R,G,B are already multiplied with the alpha value and there is no need to multiply again. > > Ex:- > A R G B > argb data 128 255 128 100 > pre-multiplied 128 128 64 50 > > So this bit, when set, would not multiply the pixel with alpha value. Ok, after staring long enough to the TRM's alpha-picture, I got it =). But having this bit always on on 3630 would mean that the software designed for 3430 would not work properly on 3630, wouldn't it? > > This patch seems to always set the bit on, never set it off. Is that the > > purpose? > > As per TRM, this bit is valid only for ARGB formats and experts suggested that we can safely assume pre-multiplied data always in real world I asked a few experts here, and they weren't so sure, and neither am I. I don't see any problems making this feature configurable, but there may be problems if it's hardcoded. So, it should be configurable. I think the default should be the same as on 3430, so that they will work similarly. Tomi -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
