| Topic: Strange light's movements
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 | Strange light's movements | |  |
| Poster | : Totem | | Posts | : 11 | | Country | : Italy | | City | : Pavia |
| | | | Posted by Totem on 17/08/2008 at 12:09:23
| | I followed the series 1 tutorials and I created a terrain with lighting. But when I rotate the terrain, the light disappears after a 90 degress rotation. Moreover i've changed the light vector to (1,1,1), because the previous one (that showed in tutorial 13) makes all dark.
Indeed, it looks like the light moves together with all the environment, but pointing in the same direction. This is the code of Draw method:
Dim WorldMatrix As Matrix = _
Matrix.CreateTranslation(-Me.TerrainWidth / 2, 0, Me.TerrainHeight / 2) * _
Matrix.CreateRotationY(Angle)
Effect.Parameters("xView").SetValue(ViewMatrix)
Effect.Parameters("xProjection").SetValue(ProjectionMatrix)
Effect.Parameters("xWorld").SetValue(WorldMatrix)
'Imposta la direzione della luce
Dim LightDirection As New Vector3(1, 1.0F, 1.0F)
LightDirection.Normalize()
'Abilita la luce
Effect.Parameters("xEnableLighting").SetValue(True)
'Imposta il vettore luce negli effetti
Effect.Parameters("xLightDirection").SetValue(LightDirection)
'Introduce un po' di luce d'ambiente. Questo evita che triangoli non
'colpiti direttamente dalla luce sia invisibili
Effect.Parameters("xAmbient").SetValue(0.1F) |
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| | | | | | Poster | : radulph | | Posts | : 218 | | Country | : germany | | City | : hamburg |
| | | | Posted by radulph on 17/08/2008 at 14:13:21
| | First, make sure, that you don't apply the world matrix on your light dir (inside the shader), as it is already given in world coordinates.
I'm pretty sure, the error comes from rotating the Normals. Remember, they don't have a position, only a direction!
First solution: Interpret the normals, not as direction, but rather as points to which your normals point to from the vertices. transform both values, and then regain the normals by subtracting the position of their end by the vertex pos. (and normalize)
Second Solution: Use the transposed inverted world matrix to transform the normals. but im not sure if it works in any case. further inverting matrices is not trivial!
;) | |
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| | | | | | Poster | : Totem | | Posts | : 11 | | Country | : Italy | | City | : Pavia |
| | | | Posted by Totem on 18/08/2008 at 12:28:26
| | I tried the second solution first: canceling world transformations on all the normals, but it does not work.
I am still trying to understand the first solution XD
If, as you said, the normals are not positions, but only directions, how would I do to subtract the vertex's position by their ends? I am quite sure you have thought a kind of recalculating operation before drawing, but I can't figure how it exactly works. | |
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| | | | | | Poster | : radulph | | Posts | : 218 | | Country | : germany | | City | : hamburg |
| | | | Posted by radulph on 18/08/2008 at 14:04:42
| | Sorry for not being that clear,
1.) Light position/direction shall not be transformed, as it is already given in world coordinates.
2.) Use the transposed inverted world matrix on the normals (not cancel transformation at all)
or the second method (unusual):
transform both the vertex-pos and the normal-point-to-pos with the world matrix,
subtract the new normal-point-to-pos from the new vertex pos, normalize
BTW, normal calculation need a normalization (sqrt == equal). It should be possible to avoid terrain rotation at all. For example one could rotate the camera instead... | |
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| | | | | | Poster | : radulph | | Posts | : 218 | | Country | : germany | | City | : hamburg |
| | | | Posted by radulph on 18/08/2008 at 14:17:08
| | ahhhhh wait! you dont even need to normalize the new normal, since its length will be still 1.
this is because rotation/translation doesn't change the distance between positions in the mesh.
excpet, of course, you would like to scale the terrain, then you would have to normalize the regained normel value.
;) | |
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| | | | | | Poster | : Totem | | Posts | : 11 | | Country | : Italy | | City | : Pavia |
| | | | Posted by Totem on 19/08/2008 at 04:30:08
| | I have ended with an easier solution: moving the camera instead of the entire terrain.
Anyway, thanks for your kindness. | |
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