OBJ, Buffer objects, and face indices

Question

I most recently had great progress in getting Vertex buffer objects to work. So I moved on to Element arrays and I figured with such implemented I could then load vertices and face data from an obj.

I'm not too good at reading files in c++ so I wrote a python doc to parse the obj and write 2 separate txts to give me a vertex array and face indices and pasted them directly in my code. Which is like 6000 lines but it works (without compiling errors). And Here's what it looks like

.

I think they're wrong. I'm not sure. The order of the vertices and faces aren't changed just extracted from the obj because I don't have normals or textures working for buffer objects yet. I kinda do if you look at the cube but not really.

Heres the render code

void Mesh_handle::DrawTri(){
    glBindBuffer(GL_ARRAY_BUFFER,vertexbufferid);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,elementbufferid);
    int index1=glGetAttribLocation(bound_program,"inputvertex");
    int index2=glGetAttribLocation(bound_program,"inputcolor");
    int index3=glGetAttribLocation(bound_program,"inputtexcoord");

    glEnableVertexAttribArray(index1);
    glVertexAttribPointer(index1,3,GL_FLOAT,GL_FALSE,9*sizeof(float),0);

    glEnableVertexAttribArray(index2);
    glVertexAttribPointer(index2,4,GL_FLOAT,GL_FALSE,9*sizeof(float),(void*)(3*sizeof(float)));

    glEnableVertexAttribArray(index3);
    glVertexAttribPointer(index3,2,GL_FLOAT,GL_FALSE,9*sizeof(float),(void*)(7*sizeof(float)));

    glDrawArrays(GL_TRIANGLE_STRIP,0,elementcount);
    //glDrawElements(GL_TRIANGLE_STRIP,elementcount,GL_UNSIGNED_INT,0);
}

My python parser which just writes the info into a file: source

The object is Ezreal from League of Legends

I'm not sure if I'm reading the faces wrong or if their not even what I thought they were. Am I suppose to use GL_TRIANGLE_STRIP or something else. Any hints or request more info.

+1 for Modern Art. The top of this...thing... actually looks like Ezrael's hairstyle, if you use your imagination xD — SingerOfTheFall
– SingerOfTheFall, Commented Aug 28, 2012 at 10:02
Since your problem is almost certainly in your .obj code, rather than your rendering code, why don't you show us where your actual problem is? — Nicol Bolas
– Nicol Bolas, Commented Aug 28, 2012 at 10:22

Andreas Brinck · Accepted Answer · 2012-08-28 10:04:12Z

4

Indices in obj-files are 1 based, so you have to subtract 1 from all indices in order to use them with OpenGL.

answered Aug 28, 2012 at 10:04

Andreas Brinck

52.8k15 gold badges87 silver badges114 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Kaliber64 Over a year ago

Nope, Unless you want a new pick it looks pretty much the same. Am I using the correct primitive?

Kaliber64 Over a year ago

I took one from all of them. I went searching and I found 1's but I can't find any 0's. Idk.

Nicol Bolas · Accepted Answer · 2012-08-28 10:22:40Z

2

First, as Andreas stated, .obj files use 1-based indices, so you need to convert them to 0-based indices.

Second:

glDrawArrays(GL_TRIANGLE_STRIP,0,elementcount);
//glDrawElements(GL_TRIANGLE_STRIP,elementcount,GL_UNSIGNED_INT,0);

Unless you did some special work to turn the face list you were given in your .obj file into a triangle strip, you don't have triangle strips. You should be rendering GL_TRIANGLES, not strips.

answered Aug 28, 2012 at 10:22

Nicol Bolas

481k66 gold badges861 silver badges1.1k bronze badges

13 Comments

Kaliber64 Over a year ago

OK so objs work in triangles I wasn't sure. Thanks a lot. I forgot that once I had the faces changed I needed to drawelements. I don't know what I was thinking with drawarrays it doesn't even use the indexes XD. minus one from faces, use triangles and draw elements. YAY! its so kaleidoscope O.o

KillianDS Over a year ago

@Kaliber64: actually, objs can have any kind of polygons, in general you have to triangulate the data first.

Kaliber64 Over a year ago

Ya I've figured a bunch out now. I found one for Quads but what is it if there are only 2 numbers per face? lines?

Kaliber64 Over a year ago

I rendered it as lines and it worked.Turns out I can't get blender to output objs with triangles or quads. Just wireframes. Max nor Maya will load the obj. says nothing to load :S.

June Wang Over a year ago

Just compared the exported .obj with Blender indices turned on, and it doesn't match

|

vasmos · Accepted Answer · 2019-07-29 15:55:30Z

0

From the image for sure your verticies are messed up. It looks like you specified a stride of 9*sizeof(float) in your glGetAttribLocation but from what I can tell from your code your array is tightly packed.

glEnableVertexAttribArray(index1);
glVertexAttribPointer(index1,3,GL_FLOAT,GL_FALSE,0,0);

Also remove stride from color/texture coords.

answered Jul 29, 2019 at 15:55

vasmos

2,5861 gold badge12 silver badges21 bronze badges

Collectives™ on Stack Overflow

OBJ, Buffer objects, and face indices

3 Answers 3

2 Comments

13 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

13 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related