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46 lines
2.1 KiB
Text
46 lines
2.1 KiB
Text
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DESCRIPTION OF PROBLEM:
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=======================
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The example map, maps/snap_plane.map, contains an example of some bugs.
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The green brush with the red face is transformed into something totally
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unexpected.
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To trigger the bug, compile the map; you don't need -vis or -light. Only
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-bsp (the first q3map2 stage) is necessary to trigger the bug. The only
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entities in the map are a light and a info_player_deathmatch, so the map will
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compile for any Q3 mod.
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SOLUTION TO PROBLEM:
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====================
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I actually came up with this regression test after reading the code to
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SnapPlane() and SnapNormal(). I decided to make this map as a test of
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whether or not I understand how the code is broken. Sure enough, the map
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is broken in the same way that I would expect it to be broken.
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The problem is that the red face of the green brush in the center of the room
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is very close to being axially aligned, but not quite. This plane will
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therefore be "snapped" to become axial. This is not the problem. The
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problem is that after the snap, the plane will be shifted a great deal,
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and the corner of the green brush will no longer come even close to meeting
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the corner of the other cube brush next to it (the two corners of the two
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brushes will drift apart a great deal).
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If you study the legacy SnapPlane() code, you will see that planes are
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defined as a unit normal and distance from origin. Well, because
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of the position of this brush on the side of the world extents (far from
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the original), the snap will cause drastic effects on the points that the
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plane was supposed to approximate.
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Another problem with SnapPlane() is that SnapNormal() snaps too liberally.
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Once SnapNormal() is changed to only snap normals that are REALLY close
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to axial (and not anything within 0.25 degrees), this bug will no longer
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appear, but the SnapPlane() problem will still be present. So, this
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regression test should be fixed BEFORE SnapNormal() is fixed, otherwise
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create another regression test with a red face that is much much closer to
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being axially aligned. We want to make sure that SnapPlane() is fixed when
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things actually do get snapped.
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The code to address these issues is currently being worked on.
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