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Asked: 2026-06-06T21:12:17+00:00

I’ve been writing an .obj loader for openGl. The geometry loads in fine, but

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I’ve been writing an .obj loader for openGl. The geometry loads in fine, but the normals are always messed up. I’ve tried to export models in 2 different programs and nothing seems to work. As far as I know, this is how you put in a normal to a GL_TRIANGLES

     glNormal3fv(norm1);   
     glVertex3fv(vert1);
     glNormal3fv(norm2);
     glVertex3fv(vert2);
     glNormal3fv(norm3);
     glVertex3fv(vert3);

(the normals are referencing to GLfloats in the rest of the code.)

EDIT: Here is a picture of a isohedron with the broken normals enter image description here

This is the full obj loader code and file:

    void loadOBJFromFile(NSString *path,float movex,float movey)
{
    NSString *contentns = [[NSString alloc]initWithContentsOfFile:path encoding:NSASCIIStringEncoding error:NULL];
    NSArray *pieces = [contentns componentsSeparatedByString:@"#"];
    //creating the arrays to read the vertecies and normals from.
    NSArray *normals = [[pieces objectAtIndex:3]componentsSeparatedByString:@"\n"];
    NSArray *vertecies = [[pieces objectAtIndex:2]componentsSeparatedByString:@"\n"];
    //The +1 is to make sure we ignore the texture/ material definition that vomes before the faces.
    int normalCount = [[normals objectAtIndex:0]intValue]+2;
    int faceCount = [[normals objectAtIndex:normalCount]intValue];
    //glTranslatef(movex, 0, movey);

glBegin(GL_TRIANGLES);
{
for (int i = 0; i < faceCount;i++)
{
    //aquires all the numbers in thye current face.
    NSArray *currentFace = [[normals objectAtIndex:normalCount+i+1]componentsSeparatedByString:@" "];
    NSArray *v1 = [[currentFace objectAtIndex:1]componentsSeparatedByString:@"//"];
    NSArray *v2 = [[currentFace objectAtIndex:2]componentsSeparatedByString:@"//"];
    NSArray *v3 = [[currentFace objectAtIndex:3]componentsSeparatedByString:@"//"];

    //crewatres the arrays to contain the vertecies
    NSArray *vertex1 = [[vertecies objectAtIndex:[[v1 objectAtIndex:1]intValue]]componentsSeparatedByString:@" "];
    NSArray *vertex2 = [[vertecies objectAtIndex:[[v2 objectAtIndex:1]intValue]]componentsSeparatedByString:@" "];
    NSArray *vertex3 = [[vertecies objectAtIndex:[[v3 objectAtIndex:1]intValue]]componentsSeparatedByString:@" "];
    //creates all the arrays for the normals
    NSArray *normal1 = [[normals objectAtIndex:[[v1 objectAtIndex:1]intValue]]componentsSeparatedByString:@" "];
    NSArray *normal2 = [[normals objectAtIndex:[[v2 objectAtIndex:1]intValue]]componentsSeparatedByString:@" "];
    NSArray *normal3 = [[normals objectAtIndex:[[v3 objectAtIndex:1]intValue]]componentsSeparatedByString:@" "];

    //creates the vertecies coordinates
    GLfloat vert1[] = {[[vertex1 objectAtIndex:1]floatValue],[[vertex1 objectAtIndex:2]floatValue],[[vertex1 objectAtIndex:3]floatValue]};
    GLfloat vert2[] = {[[vertex2 objectAtIndex:1]floatValue],[[vertex2 objectAtIndex:2]floatValue],[[vertex2 objectAtIndex:3]floatValue]};
    GLfloat vert3[] = {[[vertex3 objectAtIndex:1]floatValue],[[vertex3 objectAtIndex:2]floatValue],[[vertex3 objectAtIndex:3]floatValue]};
    //creates the normals coordinates

    GLfloat norm1[] = {[[normal1 objectAtIndex:1]floatValue],[[normal1 objectAtIndex:2]floatValue],[[normal1 objectAtIndex:3]floatValue]};
    GLfloat norm2[] = {[[normal2 objectAtIndex:1]floatValue],[[normal2 objectAtIndex:2]floatValue],[[normal2 objectAtIndex:3]floatValue]};
    GLfloat norm3[] = {[[normal3 objectAtIndex:1]floatValue],[[normal3 objectAtIndex:2]floatValue],[[normal3 objectAtIndex:3]floatValue]};

     glNormal3fv(norm1);   
     glVertex3fv(vert1);
     glNormal3fv(norm2);
     glVertex3fv(vert2);
     glNormal3fv(norm3);
     glVertex3fv(vert3);
}}
glEnd();

}

obj file:

#Wavefront OBJ file created by Hexagon 2 
mtllib object.mtl
g Form0
usemtl def_surf_mat
# 12 
v -12.533 4.78719 0 
v -12.533 20.2788 0 
v -7.74583 12.533 -12.533 
v -7.74583 12.533 12.533 
v 0 0 -7.74583 
v 0 0 7.74583 
v 0 25.066 -7.74583 
v 0 25.066 7.74583 
v 7.74583 12.533 -12.533 
v 7.74583 12.533 12.533 
v 12.533 4.78719 0 
v 12.533 20.2788 0 
# 12 
vn -0.850651 -0.525731 0 
vn -0.850651 0.525731 1.50014e-08 
vn -0.525731 -1.50014e-08 -0.850651 
vn -0.525731 0 0.850651 
vn 1.50014e-08 -0.850651 -0.525731 
vn -1.50014e-08 -0.850651 0.525731 
vn -1.50014e-08 0.850651 -0.525731 
vn 1.50014e-08 0.850651 0.525731 
vn 0.525731 0 -0.850651 
vn 0.525731 7.5007e-09 0.850651 
vn 0.850651 -0.525731 1.50014e-08 
vn 0.850651 0.525731 -1.50014e-08 
usemtl def_surf_mat
20
f 7//7 8//8 12//12 
f 7//7 2//2 8//8 
f 8//8 4//4 10//10 
f 6//6 10//10 4//4 
f 7//7 9//9 3//3 
f 5//5 3//3 9//9 
f 6//6 5//5 11//11 
f 6//6 1//1 5//5 
f 1//1 4//4 2//2 
f 1//1 2//2 3//3 
f 12//12 11//11 9//9 
f 12//12 10//10 11//11 
f 2//2 4//4 8//8 
f 10//10 12//12 8//8 
f 12//12 9//9 7//7 
f 3//3 2//2 7//7 
f 3//3 5//5 1//1 
f 4//4 1//1 6//6 
f 9//9 11//11 5//5 
f 11//11 10//10 6//6
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1 Answer

  1. Editorial Team

    The answer is very simple. The object was being loaded correctly from the object file. The loader code could be optimized a lot more. After calling,

    glEnable(GL_CULL_FACE | GL_CULL_FACE_MODE);

    EDIT
    I can’t believe I made such a newbie mistake back then. The culling face helped, but only a bit. The real problem was I was forgetting to clear the depth buffer. 

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    That should solve to problem if anyone else is also experiencing the same kind of things.

    Some of the problem was fixed, I actually needed to clear another buffer or pop the matrix or something. Now the lighting geometry loads in exactly how it appears in the editors and modeling programs. Thank you all for your help.

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