Differences

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--- tips [2019/12/14 01:29] – [Joining scraps together] refine and reorder caution about joining closed scraps brucemutton
+++ tips [2020/01/13 16:32] – clip also affects layering tarquinwj
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 As described in the Therion Book, __How the map is put together__, the layers are 'default-bottom', 'default' and 'default-top'.  'Default', as you might guess is in the middle. Areas go to the bottom, ceiling-step and chimney go to the top, everything else is somewhere in the middle.
-Now if you find that you have not drawn an entity in exactly the right order to get that special effect you were after, there is an over-ride.  There are two more 'layers', 'top', and 'bottom' and these are placed by Therion above 'default-top' and below 'default-bottom' respectively.  To put an entity in either of these layers, add the option -place top or -place bottom.  If using -place for an area it is probably a good idea to use -place for its defining border as well.
+Now if you find that you have not drawn an entity in exactly the right order to get that special effect you were after, there is an over-ride.  There are two more 'layers', 'top', and 'bottom' and these are placed by Therion above 'default-top' and below 'default-bottom' respectively.  To put an entity in either of these layers, add the option -place top or -place bottom.  If using -place for an area it is probably a good idea to use -place for its defining border as well. There is then an upper layer on top of 'top', which is the layer containing any items that have '-clip off', since these are rendered after all items that take part in normal clipping. If you have an entity without '-clip off' that needs to be rendered on top of an entity that has '-clip off' (eg. a ceiling step that must appear on top of a boulder when the boulder-edge has '-clip off'), then you will need to give the first entity (the ceiling step in the example) '-clip off' as well. These non-clipped entities are then layered with respect to each other respecting the usual -place and stacking orders.
 Fifthly, transparency and opacity settings come into it, as well as the particular viewer or printer driver you are using, as indicated in the first paragraph above.
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 **How to join scraps**
-There are three ways to join scraps;
+There are three ways to join scraps, or components of scraps;
   * fully automatically in *.th2 file,
   * semi-automatically scrap by scrap, and
   * manually line or point by point (if you must specify exactly which lines and points join).
-The last two methods are described in Thbook and all three are described below.\\
+For any particular pair of lines or points to be joined, you should only use one of these methods.  Multiple joins of the same set of objects is likely to give unpredictable results! The last two methods are described in Thbook and all three are described below.\\
 Join commands can be put directly into a survey definition, but not usually inside scrap or map definitions.