This problem took me MONTHS to resolve. First I had to laze about and ignore it for about 6 months until a new year’s resolution made me look at it again. The problem is that each patch is created independently (i.e. it might not have any neighbours yet), so when calculating the normal vectors at the edges the normal calculation is biased towards itself. It’s kinda hard to explain in words so hopefully a diagram will help:
A normal is a normalised vector perpendicular to the surface at a certain point, it might help if you imagine walking on the surface, at peaks and troughs you’ll be upright but on slopes you’ll have to compensate by leaning in (or fall over whatever floats your boat). In this example, I’m trying to work out what the normals are for the green “patch” (the green V) and I don’t yet have the blue or the red patch. So I have to calculate a normal (pink arrows) for each of the 3 points in the green patch using just those 3 points.
I can work out the centre normal fully using the 2 adjacent points to the left and the right. However the left and right normals only have 2 points available (left & centre for the left normal, right & centre for the right normal) for normal calculation and so they end up perpendicular to the left and right vectors. When the red patch comes along it happens to work out well, the normal on the right indicates a slope. Unfortunately when the blue patch comes along it will look wrong. The left normal should be pointing straight up because it’s a peak, not a slope. If that wasn’t enough, to make matters worse when the blue patch works out its right normal it will look like a slope in the opposite direction so lighting will shade the slopes with a very sharp divide at the top.
In order to solve I could redo neighbouring normals whenever a new patch is generated but this would cause lots of rewriting the vertex buffer & would be visually obvious until the neighbouring patch was created. The way I opted for was to extend the patch area by one cell (equivalent to getting the middle point of the blue and red patches) and work out normals for all the inner points (same number of points as in the unextended patch). It worked out pretty well, here’s a before and after shot where latitude lines disappear:
And a close up with pink normals. On the peak in the before shot there’s divergence with normals at the same point going different directions. In the after shot the normals on the peak look like one normal but really they are 4 different normals all pointing in the same direction:
It’s a bit less obvious but on the mountain side you can see some lines caused by divergent normals where patches meet in the before shot disappear in the after. I made a gif to show gifferences but the 256 colour palette isn’t the best:
I think I’ll have a little look at texturing next, to get the planet looking like the terrain I had SEVERAL years ago… pretty shameful thinking this is progressing so slow but sure I’ll keep tapping away at it, one day at a time*.
*time may be anything from 6 months to a year or two!
2 comments:
Glad to see you are back, well I cant really say glad because it is just another medium to remind me how lazy and slack I also am.
Yeah well let's see how long it lasts! Had another look at your blog there, you've done a load over the years - I'm almost back at square one except the terrain's round now.
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