# Problem with ... normals?

Started by Jun 21 2001 05:44 AM

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5 replies to this topic

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#1
Members - Reputation: **122**

Posted 21 June 2001 - 05:44 AM

Look the picture at http://www4.uji.es/~al024870/misc/cube.jpg and you will see what''s my problem.
It''s a cube with light and a green texture. I use vertex arrays with the vertices, the texture coordinates and the normals. All is read from an OBJ file. And the models are made with Nendo.
What''s wrong? May be the normals? I think they are per vertex normals. I have tried more complex objects (airplanes, buildings). All look similar and no one is smooth even with GL_SMOOTH enabled.

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#2
Members - Reputation: **1323**

Posted 21 June 2001 - 09:22 AM

In order for GL_SMOOTH to take effect, you must calculate, and send the normals to OpenGL. Here is the function that I use to calculate a normal:

Note that this function is *REALLY* a speed hazard. Especially the call to

------------------------------

Trent (ShiningKnight)

E-mail me

OpenGL Game Programming Tutorials

Edited by - ShiningKnight on June 21, 2001 4:26:55 PM

void ComputeNormal(VECTOR3D* v1, VECTOR3D* v2, VECTOR3D* v3)

{

VECTOR3D a(0.0f, 0.0f, 0.0f);

VECTOR3D b(0.0f, 0.0f, 0.0f);

VECTOR3D result(0.0f, 0.0f, 0.0f);

float length;

a.vertex[0]= v1->vertex[0] - v2->vertex[0];

a.vertex[1]= v1->vertex[1] - v2->vertex[1];

a.vertex[2]= v1->vertex[2] - v2->vertex[2];

b.vertex[0]= v1->vertex[0] - v3->vertex[0];

b.vertex[1]= v1->vertex[1] - v3->vertex[1];

b.vertex[2]= v1->vertex[2] - v3->vertex[2];

result.vertex[0]= (a.vertex[1]*b.vertex[2]) - (b.vertex[1]*a.vertex[2]);

result.vertex[1]= (b.vertex[0]*a.vertex[2]) - (a.vertex[0]*b.vertex[2]);

result.vertex[2]= (a.vertex[0]*b.vertex[1]) - (b.vertex[0]*a.vertex[1]);

//Calculate the length of the normal

length= (float)sqrt(SQUARE(result.vertex[0]) +

SQUARE(result.vertex[1]) +

SQUARE(result.vertex[2]));

//Normalize, and send to OpenGL

glNormal3f(result.vertex[0]/length, result.vertex[1]/length, result.vertex[2]/length);

Note that this function is *REALLY* a speed hazard. Especially the call to

` sqrt(...) `

. Owwww------------------------------

Trent (ShiningKnight)

E-mail me

OpenGL Game Programming Tutorials

Edited by - ShiningKnight on June 21, 2001 4:26:55 PM

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#5
Members - Reputation: **122**

Posted 22 June 2001 - 02:24 AM

Maybe you could draw the normals.

VECTOR3 a,b,c; // the points for a triangle

VECTOR3 m = (a + b + c) / 3.0; // center of the triangle

VECTOR3 e = m + normal * 10.0; // end of normal line

glBegin(GL_LINES);

glVertex3f(m.x, m.y, m.z);

glVertex3f(e.x, e.y, e.z);

glEnd();

But from the look of the cube i would guess the x and z (or other combination) coordinates are swaped...

VECTOR3 a,b,c; // the points for a triangle

VECTOR3 m = (a + b + c) / 3.0; // center of the triangle

VECTOR3 e = m + normal * 10.0; // end of normal line

glBegin(GL_LINES);

glVertex3f(m.x, m.y, m.z);

glVertex3f(e.x, e.y, e.z);

glEnd();

But from the look of the cube i would guess the x and z (or other combination) coordinates are swaped...

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#6
Members - Reputation: **122**

Posted 22 June 2001 - 11:49 AM

The problem was that Nendo saves the normals incorrectly, because when using a converter I get the expected results. Well, not exactly what I expected ...

Now I have another problem. All is tinted in blue!! I don''t use alpha and nor the light nor the materials have a great blue component. Any idea of what is the error?

Thanks for the tip of drawing the normals!!

Now I have another problem. All is tinted in blue!! I don''t use alpha and nor the light nor the materials have a great blue component. Any idea of what is the error?

Thanks for the tip of drawing the normals!!