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revision 1.2 by tjl, Tue Aug 27 04:32:18 2002 UTC revision 1.3 by benja, Tue Aug 27 06:07:46 2002 UTC
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2  <html>  <html>
3  <head>  <head>
4    <title>PEG 1003</title>    <title>PEG 1003</title>
5          
6    <meta http-equiv="content-type"    <meta http-equiv="content-type"
7   content="text/html; charset=ISO-8859-1">   content="text/html; charset=ISO-8859-1">
8  </head>  </head>
9    <body>    <body>
10    
11  <h1>PEG 1003: Fix hierarchical <tt>VobScene</tt>s</h1>  <h1>PEG 1003: Fix hierarchical <tt>VobScene</tt>s</h1>
12    <p><i>
13    Author: Tuomas Lukka
14    </i></p>
15    
16  <p>Hierarchical <tt>VobScene</tt>s need some fixing.<br>  <p>Hierarchical <tt>VobScene</tt>s need some fixing.<br>
17   </p>   </p>
18    
19  <p>Open issues:<br>  <p>Open issues:<br>
20   </p>   </p>
21    
22  <ul>  <ul>
23     <li>Is the integer identifier of the coordinate system into which to place     <li>Is the integer identifier of the coordinate system into which to place
24  a new coordinate system appropriate?</li>  a new coordinate system appropriate?</li>
25     <li>Should plain coordinate systems be usable as those ints?</li>     <li>Should plain coordinate systems be usable as those ints?<br>
26             <small>(Benja:) "Plain coordinate systems"?</small>
27       </li>
28    
29    <ul>    <ul>
30       <li>What are the semantics there? Current, just translate, is not good.       <li>What are the semantics there? Current, just translate, is not good.
31  However, using the vob-internal CS is not really nice either, as Vob CSs usually  However, using the vob-internal CS is not really nice either, as Vob CSs usually
32  are in pixels, and this would be in 10s or 100s of pixels per unit.</li>  are in pixels, and this would be in 10s or 100s of pixels per unit.<br>
33           (Benja:) I think use the parent cs to translate and optionally give a scale
34         when creating the sub-cs, and use the parent for clipping. I think this
35         serves well in the usual case.
36         </li>
37    
38    </ul>    </ul>
39     <li>The most general use case is the PP-like viewport. How is that implemented?     <li>The most general use case is the PP-like viewport. How is that implemented?
40  You need</li>  You need
41      
42    <ul>    <ul>
43       <li>clipping</li>       <li>clipping</li>
44       <li>separate coordinate system for the motion of the clipping rectangle       <li>separate coordinate system for the motion of the clipping rectangle
45  and the contents</li>  and the contents</li>
46      
47    </ul>    </ul>
48    
49      <p>(Benja:) I thought rotation/scaling? The above is extremely easy to do by
50         putting two cs into each other, the parent being used for clipping,
51         and the child being used for the contents.
52      </p>
53    
54      </li>
55    
56  </ul>  </ul>
57  Possible solutions:<br>  Possible solutions:<br>
58  <ul>  <ul>
# Line 44  Possible solutions:<br> Line 60  Possible solutions:<br>
60  system defines a clip rectangle. How about specifying the coordinate system  system defines a clip rectangle. How about specifying the coordinate system
61  to clip to when creating a (any) coordinate system, as well as the coordinate  to clip to when creating a (any) coordinate system, as well as the coordinate
62  system into whose coordinates the given coordinate system should go.<br>  system into whose coordinates the given coordinate system should go.<br>
63      <small>(Benja:) This doesn't serve well in the usual viewport case, where
64             you have:
65             <ul>
66                 <li>A thing you want to view (e.g. a PP paper, the contents
67                     of a cell)</li>
68                 <li>A place inside that thing where your focus is (you want to
69                     view the stuff around the focus)</li>
70                 <li>An area on the screen where you want to show the viewport
71                     (so that the focus is shown in the middle of the viewport,
72                     and as much of the viewed thing is shown around the focus
73                     as fits in the viewport).
74             </ul>
75             Calculating the position of the viewed thing relative to the viewport
76             is easier than calculating the absolute position of the viewed thing
77             on the screen: to calculate the position relative to the viewport,
78             you don't need to know the viewport's position, just the focus;
79             to calculate the absolute position on the screen, you need both,
80             essentally translating the focus coordinates by the viewport's.
81             <br><br>
82             Therefore, I think that there is no need to special-case this in
83             the API, as it's easier to do with two nested cs.
84      </small>
85    </li>    </li>
86  </ul>  </ul>
87   <br>   <br>

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