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[css-transforms] perspective description and illustration misleading

From: Alan Gresley <alan@css-class.com>
Date: Sun, 13 Jul 2014 22:25:10 +1000
Message-ID: <53C27AA6.2090304@css-class.com>
To: CSS 3 W3C Group <www-style@w3.org>, "public-fx@w3.org" <public-fx@w3.org>
Hello all,

The is a follow up to my reply to Dean Jackson's message from October 
last year [1]. In my reply, I said the below:


   | The illustration and assumed eye position is
   | misleading because none of this is really happening
   | because every thing is relative and somewhat anchored
   | to the veiwport or z plane. We only trick the viewer
   | into believing that they are positioned in 3D space
   | as a painting on some wall does.

What I mean by the above is that what is really happening is the 
vanishing point or point of perspective is behind the drawing surface or 
picture plane [2] and not in front of it unless the value (must always 
be positive) for the Z axis is greater than the value for perspective 
(e.g. 'translateZ: 600px' together with 'perspective: 400px').

I have attached a graphic (perspective_distance-b.png) demonstrating 
this more correct way of visualizing where the vanishing point is in 
respect to drawing surface which is very different to the Figure 3 in 
section 6.1 of CSS Transforms [3]. Below is a interactive demo (working 
correctly in Firefox and IE12).

http://css-class.com/test/css/3/perspective/depth-of-field.htm


1. http://lists.w3.org/Archives/Public/public-fx/2013OctDec/0002.html
2. http://en.wikipedia.org/wiki/Picture_plane
2. http://dev.w3.org/csswg/css-transforms/#3d-transform-rendering


Alan

-- 
Alan Gresley
http://css-3d.org/
http://css-class.com/


perspective_distance-b.png
(image/png attachment: perspective_distance-b.png)

Received on Sunday, 13 July 2014 12:25:43 UTC

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