From: Chris Marrin <cmarrin@apple.com>

Date: Thu, 08 Dec 2011 15:11:02 -0800

Cc: Matt Woodrow <mwoodrow@mozilla.com>, Daniel Glazman <daniel.glazman@disruptive-innovations.com>, www-style@w3.org

Message-id: <68CD2517-0050-4296-ACBE-6CE51FB7065A@apple.com>

To: "L. David Baron" <dbaron@dbaron.org>

Date: Thu, 08 Dec 2011 15:11:02 -0800

Cc: Matt Woodrow <mwoodrow@mozilla.com>, Daniel Glazman <daniel.glazman@disruptive-innovations.com>, www-style@w3.org

Message-id: <68CD2517-0050-4296-ACBE-6CE51FB7065A@apple.com>

To: "L. David Baron" <dbaron@dbaron.org>

On Dec 7, 2011, at 5:36 PM, L. David Baron wrote: > On Wednesday 2011-12-07 16:41 -0800, Chris Marrin wrote: >> On Dec 1, 2011, at 1:39 PM, L. David Baron wrote: >>> On Thursday 2011-12-01 13:24 -0800, Chris Marrin wrote: >>>> On Nov 29, 2011, at 12:13 PM, Matt Woodrow wrote: >>>>> This seems like the right interpretation to me, but I believe the matrix definition for rotate3d() in the spec needs to be updated to reflect this. >>>> >>>> I'll look at it. What error(s) do you see? >>> >>> Firefox implements the matrix definition of rotate3d that's given >>> in the spec, and everyone seems to agree that rotates in the wrong >>> direction. Given that, I think the fix would be that all the terms >>> with sin(angle) should have their sign reversed. >> >> How do you mean it rotates in the wrong direction? rotate(45deg) and rotate3d(0,0,1, 45deg) both rotate in the same direction, right? > > Everyone is saying they should. But according to the spec they > shouldn't, since: > rotate(45deg) > == (per SVG 1.1 explicitly, and also implicitly in CSS) > matrix(cos(45deg), sin(45deg), -sin(45deg), cos(45deg), 0, 0) > == (explicitly based on 3d-transforms) > matrix3d(cos(45deg), sin(45deg), 0, 0, > -sin(45deg), cos(45deg), 0, 0, > 0, 0, 1, 0, > 0, 0, 0, 1) > > But according to css3-3d-transforms: > rotate3d(0, 0, 1, 45deg) > == (based on the definition of rotate3d()) > matrix3d(1 + (1-cos(45deg))*(0*0-1), -1*sin(45deg)+(1-cos(45deg))*0*0, 0*sin(45deg)+(1-cos(45deg))*0*1, 0, > 1*sin(45deg)+(1-cos(45deg))*0*0, 1 + (1-cos(45deg))*(0*0-1), -0*sin(45deg)+(1-cos(45deg))*0*1, 0, > -0*sin(45deg)+(1-cos(45deg))*0*1, 0*sin(45deg)+(1-cos(45deg))*0*1, 1 + (1-cos(45deg))*(1*1-1), 0, > 0, 0, 0, 1) > == (reducing) > matrix3d(cos(45deg), -sin(45deg), 0, 0, > sin(45deg), cos(45deg), 0, 0, > 0, 0, 1, 0, > 0, 0, 0, 1) > > So I think the signs of all the sin(angle) terms in the definition > of rotate3d() need to be flipped, which is equivalent to transposing > the matrix. > > (I could certainly see ending up the wrong way by accident given > confusion over which way matrix3d() describes a matrix and whether > it's for row vectors or column vectors.) Ok, I understand. This is probably due to the fact that a while back we changed from row to column major matrices and I failed to fix this formula. I'll fix it... ----- ~Chris cmarrin@apple.comReceived on Thursday, 8 December 2011 23:55:02 UTC

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