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setting indices help

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I am parsing an .OBJ file , i have the vertices information fine, now i am trying to figure out how to get the indice information from the .obj in to a d3d9 indicebuffer


This is my obj file


# 3ds Max Wavefront OBJ Exporter v0.97b - (c)2007 guruware
# File Created: 11.09.2013 04:25:50
mtllib box.mtl
# object Box001
v  -9.7117 0.0000 9.9218
v  -9.7117 0.0000 -9.9216
v  10.1316 0.0000 -9.9216
v  10.1316 0.0000 9.9218
v  -9.7117 16.0360 9.9218
v  10.1316 16.0360 9.9218
v  10.1316 16.0360 -9.9216
v  -9.7117 16.0360 -9.9216
# 8 vertices
g Box001
usemtl wire_088088225
s 2
f 1 2 3 4 
s 4
f 5 6 7 8 
s 8
f 1 4 6 5 
s 16
f 4 3 7 6 
s 32
f 3 2 8 7 
s 64
f 2 1 5 8 
# 6 polygons
In this text i understand the indices are below usemtl wire_088088225, i just dont understand how to get them in to Directx's indice buffer, can anyone help?

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The first thing to realise is that indices in OBJ files start at 1, not 0, so you'll have to subtract 1 from every index value when you read them in.


Secondly, the OBJ format allows faces to be defined with 3 or more vertices and may require triangulation since directX has triangle-based faces. For 4-vertex faces you might be able to assume which vertices define the shared edge between the 2 triangles and create 2 faces in your index buffer.


Thirdly, the OBJ format allows each vertex of a face to record several pieces of information separated by the "/" symbol. The first index is the index of the vertex position data. The second value is the index of the UV coordinate and the third is for the normal, so you have to be careful when parsing data from other OBJ files that may contain these. Here is an example of a face defined with additional data:


f 1/8/7 2/9/7 3/9/7 


Note: it's valid for data to be skipped as well, eg: f 1//7 2//7 3//7 (same as before, but no UV coordinates).


I hope that helps.




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what does the s mean that goes up each time

what is the totally amount of indices for this model?

s stands for smoothing groups, meaning that vertices that are a part of a smoothing group use the average of the face normals of the faces that it shares. A cube for example would consist of 12 trianglular faces, and 6 smoothing groups, because the  triangles of each side share the same normal.( note: 0 smoothing groups also work, because the averaging of face normals will result in the same normal as the face normal that each vertex belongs to) If you wanted a half dome, the faces on the flat disk at the bottom would belong to a group(again: or not because they all share the same normal anyway) while the hemisphere vertices would belong to a smoothing group(this must be done, to get the normals correct. If your familiar with blender, it is the difference between flat and smooth shading.


the entire model needs to be parsed to be sure how many indices are in it, as  vertex data may or may not be shared by several faces, and if they belong to separate smoothing groups, they will need to be duplicated in the mesh.


for your mesh, parse the vertices into a temporary storage, since you have quads, you'll need to get triangles first. the winding order will tell you which way to split, and also help calculate the normal. for each smoothing group, for each face you process, add its normal to an std::vector for each vertex that is part of that face using the vertex number as the index., and increment a counter for each vertex did that to. At the end of the s group, your counter will tell you how many faces that vertex was part of, divide your normal by that, and that will be the normal to use in your mesh. push those processed verts into your mesh with indices, reset the counters, clear the normals and parse the next group

Edited by Burnt_Fyr

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