1 Sep 2006 09:31
Problem with glCullFace(GL_BACK) in the player.c
Hello, I have a 3ds model(http://195.14.170.84/test.zip) there "culled" faces should be front side, not back. ( static void init(void)... glCullFace(GL_BACK); ) (Also I tested this model with 3d max. 3D Max shows model fine ) player.c has code: if( mat->two_sided ) glDisable(GL_CULL_FACE); else glEnable(GL_CULL_FACE); I think that after glEnable(GL_CULL_FACE) should be defined "culling" face side. I was trying to eliminate this problem, but I had failed.. Changing glCullFace(GL_BACK) to the glCullFace(GL_FRONT) http://195.14.170.84/test.zip model looks ok, but other models not. Also I noticed that changing face points direction (player.c: for i = 2 i != -1; --i) also solves defined problem. Maybe it as any attribute in the material which defines culling side?(Continue reading)
Problem:
Vertices normals are incorrectly calculated for "cube.3ds".
I investigated this and came to the following conclusion:
*Error with vertices normals calculation is inherited from 3DS format
itself.*
That's because in 3DS there is no separation between points indices and
uv indices.
Such separation of course is possible in modeller - 3DSMax: max's face
looks a bit like this:
class MaxFace
{
public:
int points[3];
int texCoords[3];
unsigned int smoothing;
};
If for example in modeller(3DSMax) we have two faces with same smoothing
group and sharing two points but having different uv coordinates:
maxface0
points = 0, 1, 2;
texCoords = 0, 1, 2;
smooth = 2;
maxface1
points = 1, 0, 3;
texCoords = 3, 4, 5;
smooth = 2;
- such model will be incorrectly exported to old 3DS format. Exporter
will detect different texCoords and will duplicate shared points to get
"one point - one texCoord" situation:
3dsface0
points = 0, 1, 2;
smooth = 2;
3dsface1
points = 4, 5, 3;
smooth = 2;
with points 4 and 5 being clones of 1 and 0.
And because vertices normals may be smoothed only between same points
the lighting will be obviously incorrect.
Resolution:
Because of format shorthcomings we need additional post-loading
preprocess pass to recover informations lost during export to 3DS.
Suprisingly it's quite easy and possible.
First we need to introduce new "class Lib3dsFace2" with separate indices
for uv tex coords:
class Lib3dsFace2: public Lib3dsFace
{
public:
Lib3dsWord texCoords[3];
};
second post-loading preprocess in three steps:
Step 1. Create new list of "Lib3dsFace2" and copy old "Lib3dsFace" faces
to this. Also to ensure correct texCoords indices we need to copy
"Lib3dsFace::points" to "Lib3dsFace2::texCoords".
Step 2. We need to identify duplicated points and then replace clones
with first original point:
for( int i = 0; i < mesh->points; ++i )
{
if( processedPoints[i] )
continue;
for( j = i + 1; j < mesh->points; ++j )
{
if( processedPoints[j] )
continue;
#define EPSILON 0.01f
if( ( fabs( mesh->pointL[i][0] -
mesh->pointL[j][0] ) < EPSILON ) &&
( fabs( mesh->pointL[i][1] -
mesh->pointL[j][1] ) < EPSILON ) &&
( fabs( mesh->pointL[i][2] -
mesh->pointL[j][2] ) < EPSILON ) )
{
/// <at> todo: replace every occurence of
"j" point with "i"
for( int k = 0; k < mesh->faces; ++k )
for( int l = 0; l < 3; ++l )
if(
mesh->faceL[k].points[l] == j )
mesh->faceL[k].points[l] = i;
processedPoints[j] = true;
}
}
}
Step 3.
Calculate vertices normals, this time they will be correct.
<Code is too complicated to put here.>
Well, that's all folks. Sorry for being too bloated.
Hope that will help.
Rafał Kamraj
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