Re: Linear gradients, Transforms and angles...

On Mon, Sep 27, 2010 at 10:12, Chris Marrin <cmarrin@apple.com> wrote:

>
> Ok, I think we've both stated our positions sufficiently. I still believe
> the subtlety between the two concepts is too fine for the average author to
> grasp. But I think we're well into the territory of bikeshedding here, so
> I'll stop trying to make that point. I'll agree to the consensus on this
> issue.
>
>
I'd like to think I'm an average author (though being on this list in the
first place may disqualify me). Whether it is intuitive, or because I have
(sparingly) used Photoshop-like programs in the past, or because I paid
attention in trigonometry, I agree with Brad's point of view, and have since
the discussion started, though I have tried the other arguments on for size.
A direction is different from an angle, and people are used to thinking
about them in different ways.

When things are rotated, they *move* from their current orientation to a new
one *through* a number of degrees in a direction, and counting 'upright' as
the 'current orientation' and designating clockwise as the direction makes a
lot of sense, since, in my experience, that's generally how people think
about and describe rotation.

When people think about a direction, they measure the offset *against* a
baseline. While the concept of 'heading' measures a direction against north
and measures the clockwise angle, I think more people are familiar with the
concepts taught in geometry and trigonometry, where the offset is a
counterclockwise angle measured against east. (Also, the concept of heading
invokes the idea that the imaginer is the point from which the directional
vector originates and that north is the direction the imaginer is facing on
the plane they are standing on, whereas the concept for geometry invokes the
idea that the direction is on a plane in front of the imaginer, as if on a
screen or piece of paper.)

It may also be true that, if we were to completely adhere to that style, we
should flip the y-axis and measure the offset clockwise, I think *that*
would be too confusing to the average author, as it is a style that is used
nowhere - not even in Photoshop-like programs, where the positive y-axis
points downward.

-Eli Morris-Heft