From: Brad Kemper <brad.kemper@gmail.com>

Date: Tue, 7 Sep 2010 15:46:46 -0700

Message-Id: <AC671683-185A-47E8-A24C-383F8D011B68@gmail.com>

Cc: fantasai <fantasai.lists@inkedblade.net>, "www-style@w3.org" <www-style@w3.org>

To: "Tab Atkins Jr." <jackalmage@gmail.com>

Date: Tue, 7 Sep 2010 15:46:46 -0700

Message-Id: <AC671683-185A-47E8-A24C-383F8D011B68@gmail.com>

Cc: fantasai <fantasai.lists@inkedblade.net>, "www-style@w3.org" <www-style@w3.org>

To: "Tab Atkins Jr." <jackalmage@gmail.com>

Brad Kemper On Sep 7, 2010, at 2:20 PM, "Tab Atkins Jr." <jackalmage@gmail.com> wrote: > On Tue, Sep 7, 2010 at 1:50 PM, fantasai <fantasai.lists@inkedblade.net> wrote: >> We seem to have multiple notions of how angles should work. >> >> There are two commonly-taught methods of mapping angles to directions: >> - the Bearing Angle Method >> - the Cartesian Angle Method >> There are other methods of mapping angles to directions: >> - the Graphical Angle Method >> >> Bearing Angle Method: >> - Used for compass bearings >> - Zero degrees points north/up >> - Angles increase clockwise >> - Used by the following properties: >> azimuth (CSS2) >> glyph-orientation (SVG, XSL) >> image-orientation (Paged Media) >> >> Cartesian Angle Method: >> - Determined by arctan(slope) in a Cartesian coordinate system with >> x-values increasing rightwards and y-values increasing upwards >> - Zero degrees points right >> - Angles increase counter-clockwise >> - Used by the following: >> CSS gradient notation (implied by illustrations in CSS3 Images) >> >> Graphical Angle Method >> - Determined by arctan(slope) in a graphics coordinate system with >> x-values increasing rightwards and y-values increasing downwards >> - Zero degrees points right >> - Angles increase clockwise >> - Used implicity by the following: >> Scalable Vector Graphics (SVG) >> CSS 2D Transforms >> >> Of the two that fall under the Graphical Angle method, afaict neither >> uses absolute angles -- the zero point doesn't matter, only the clockwise >> increase. Which makes SVG and Transforms compatible with the Bearing Angle >> Method from a user perspective. >> >> This makes the gradient syntax the odd one out. Therefore its use of angles >> should be >> a) defined in the prose somewhere instead of implied by illustration >> b) use the Bearing Angle Method, i.e. 0deg points up and angles increase >> clockwise >> >> Furthermore, the CSS3 Values and Units module should make this convention >> explicit so that later spec-writers don't make the same mistake. (Also, >> the outdated reference to ACSS and the 0-360 normalization requirement >> should be removed.) > > Argh, I was hoping I could avoid this, but it seems like I maybe can't. ;_; > > Anybody have any strong objection to me switching the <angle> > reference to Bearing Angles? > > ~TJ > Yes.Received on Tuesday, 7 September 2010 22:48:52 UTC

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