Re: Linear gradients, Transforms and angles...

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Mon, 20 Sep 2010 14:07:19 -0700
Message-ID: <AANLkTi=+TsM_Op==dBTCXECpvEe45SGB7mT6O-n4+RfS@mail.gmail.com>
To: Chris Marrin <cmarrin@apple.com>
Cc: Brad Kemper <brad.kemper@gmail.com>, Simon Fraser <smfr@me.com>, Daniel Glazman <daniel.glazman@disruptive-innovations.com>, "L. DavidBaron" <dbaron@dbaron.org>, www-style list <www-style@w3.org>
```On Mon, Sep 20, 2010 at 2:01 PM, Chris Marrin <cmarrin@apple.com> wrote:
> Angle is a concept that I believe is fairly new to CSS, so I don't think there is much of a precedent here. Using the math we are using in CSS transforms, rotation follows the "right hand rule". Hold your right hand so your fingers are curled and your thumb is pointing out. Your thumb indicates the direction vector of the axis of rotation and your fingers curl in the direction of rotation. Since the positve Z axis goes into the screen for CSS transforms, that means positive rotation angles go clockwise.

"In three dimensions, a Z axis is added, with positive z values
conceptually rising perpendicularly out of the window toward the user
and negative z values falling into the window away from the user."

The positive Z axis comes out of the window, not goes in.  By your
logic, rotations should treat CCW as positive.

> Where rotations "start" is a matter of convention. Analog clocks start at 12 o'clock (bottom to top), In geometry, a 0 degree rotation is typically represented by a vector along the positive X axis. But again, that's all convention.

Note that the default rotation direction between analog clocks and
geometry are opposite.

~TJ
```
Received on Monday, 20 September 2010 21:08:11 UTC

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