In the Graphics Display Options dialog box there is a new section for "Sketchy Lines"
- Firstly there is an "Enable" checkbox to turn the effect on or off - initially it seems to do nothing because the default slider settings are zero.
- Jitter does two things: as the slider increases, all the straight lines in the view become more wavy; at a certain point the lines start doubling up, and then becoming multiple lines - so you get a combination of the two effects somewhat like running a pencil back and forth to emphasise a line.
- Extension does what you expect from the name - it "virtually" extends the lines past their real end points or intersections. The extension obviously increases with the slider value, but it is not an equal extension on each line - it is proportional to the length of the line
It seems like the line extensions and jitter are applied to the model before any hidden line removal is done - this means that all lines are jittered/extended even if they would ultimately not be visible in a normal hidden line view. This has some unexpected side effects that you need to be aware of:
- Jittery lines seem to be actually waving in 3D, which explains why you will see sections of jittered lines disappear as they duck into or behind an adjacent surface. On the roof in the Revit sample file that looks quite good because you don't want to emphasise the roof stripes. Once you bump up the level of jitter past the halfway mark it starts to create multiple lines so that in most instances where a line partially disappears another one will be waving the other way so it remains visible.
- On an outside edge the effect is less obvious - in fact it tends to emphasise horizon lines as the lines are less likely to be hidden by adjacent surfaces.
- On an inside edge the effect is the opposite - the lines are even more likely to disappear as they have much more chance of being hidden by a surface - have a look at the coving on this image
- Jitter is applied equally to all lines, categories, element types, internal and external edges, silhouettes, depth of view, scale etc. What this means is that some elements get much darker as soon as you enable jitter - such as railings and window frames. This is partly due to previously close parallel lines now overlapping, but also due to the multiple line effect on higher levels of jitter. It is currently not possible to be specific about which elements become more jittery than others. It may become necessary to start applying overrides like halftone to certain categories, so that they do not dominate.
- Line extensions can have unexpected results if you bump the slider up too high - lines from elements that should be totally hidden can start showing through surfaces. On the Revit sample house there are some internal walls (?) that start to project through the roof; balcony lines project right through the side wall.
- This effect is also dependant on the overall line lengths, as shorter lines generally extend less at their ends. The overall effect is more sketchy but the random lines might confuse people - so you need to balance the extension settings to match your desired effect.
- If you have a few persistent line extensions you can always use the Linework Tool to make them invisible. Likewise where jitter makes too many lines on a particular element - the Linework Tool will be your friend (or enemy if there are too many lines and not enough time!).