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texture mapping using OpenGL

Started by Xtreme Apr 22, 2001 at 5:55 PM 12 replies 750+ views

Original Post

Apr 22, 2001 at 5:55 PM

hi there... I have a problem where I created a 3d object using glBegin(GL_LINES) and using glVertex3f() to specify the points. So, the 3d wireframe is ok. But when I try to put some texture on it, by using glBindTexture, etc, I still get a wireframe model but the wireframe itself are textured! I don''t want a wireframe anymore, I want a solid model (textured of course). Where am I going wrong? Xtreme.

Maximus

Apr 22, 2001 at 6:04 PM

Try using GL_TRIANGLES to draw your models. GL_LINES, as the name suggests, will only draw lines.

Xtreme

Author

Xtreme

Apr 22, 2001 at 6:18 PM

THANKS! that worked

BUT!

if I don''t texture it, i get multiple lines instead of the required ones. How can I get rid of the extra lines used to make up the mesh?

Maximus

Apr 22, 2001 at 6:50 PM

Could be due to previously using GL_LINES instead of GL_TRIANGLES. You might be trying to draw much more than neccessary but still getting the same effect when textured.

Xtreme

Author

Xtreme

Apr 22, 2001 at 6:59 PM

actually quite the opposite! I can see that more (unnecessary) lines are drawn with GL_TRIANGLES. but its ok with GL_LINES.
But, when I decide to put a texture on it, the one with GL_TRIANGLES comes out solid while the one with GL_LINES is textured in wireframe only.

Also, how can I divide up the textures in the whole 3d wireframe so that I can have I have say one texture on the body, a different one on the arms, etc... (that is, having multiple textures on the one object?) Currently, this texture is mapping to every single part of the object!

Xtreme

Author

Xtreme

Apr 22, 2001 at 7:03 PM

currently this is how I implemented it:

  
glEnable(GL_TEXTURE_2D);
//glEnable(GL_BLEND);


glBindTexture(GL_TEXTURE_2D, texId[2]);
glEnable(GL_TEXTURE_GEN_S);
glEnable(GL_TEXTURE_GEN_T);
glTexGenf(GL_S,GL_TEXTURE_GEN_MODE,GL_SPHERE_MAP);
glTexGenf(GL_T,GL_TEXTURE_GEN_MODE,GL_SPHERE_MAP);

glBegin(GL_TRIANGLES);
//draw object using glVertex3f() only

glEnd();

glDisable(GL_TEXTURE_GEN_S);
glDisable(GL_TEXTURE_GEN_T);
glDisable(GL_TEXTURE_2D);
//glDisable(GL_BLEND);

Now, with this, I get one texture mapped to all of the object, how can I divide it up?

zedzeek

164

zedzeek

Apr 22, 2001 at 8:17 PM

i dont really understand what u want to do
do u want to draw the solid model textured
and then afterwards draw a wireframe version of the model over the top of it so u can see the individual tris of the solid model.

http://members.xoom.com/myBollux

Xtreme

Author

Xtreme

Apr 22, 2001 at 8:30 PM

zeedzeek, i don''t want a wireframe model. (i just did that to see if the lines were drawn right).

I want a solid model but since I made this model from one piece (that is, from glvertex3fs) I now want parts of the object to be texture mapped with not just one, but multiple textures.

Is that possible?

zedzeek

164

zedzeek

Apr 23, 2001 at 5:06 PM

to use multiple textures u have to break your model(mesh) up into multiple meshes cause u cant go
glBegin(GL_TRIANGLES)
vertex,vertex,vertex etc
bind another texture
vertex,vertex,vertex etc
bind another texture
vertex,vertex,vertex etc
glEnd( );

http://members.xoom.com/myBollux

Xtreme

Author

Xtreme

Apr 23, 2001 at 11:19 PM

so in other words, you are saying to attach a separate texture, i must use glBegin() and glEnd() separately? which means I have to break up the object into several objects?

Ingenu

132

Ingenu

Apr 24, 2001 at 3:21 AM

OpenGL is based on triangles not mesh, so yes.

Maybe you should read the OpenGL doc, cause it''s explains how OpenGL works...

There''s a link to an electronic version of the Red book on nehe.gamedev.net

-* So many things to do, so little time to spend. *-

kren

Apr 25, 2001 at 7:50 AM

you can also use squares (GL_QUADS)instead of triangles. sometimes they''re even more useful

smitty1276

117

smitty1276

Apr 26, 2001 at 11:28 PM

Guys... I never thought about this before, because I''ve never had a reason to try it. Is it possible to bind multiple textures to one polygon by specifying mapping coordinates? As an example, could I map a quad with 4 seperate textures on each "corner"?

kren

Apr 28, 2001 at 8:00 AM

probably yes. but watch out for textures width&height because if textures are too big there is VERY big chance that the program will report error.but why don''t you use 4 quads instead of just 1? you must just be careful at coordinates!!!

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