Implementation: Importing WaveFront OBJ Models

Overview 

As discussed before, WaveFront OBJ and MTL files needs to be parsed to get geometry, Material information. A new mesh class and new geometry object are required for this.

Details

A new mesh class  WFObjMesh is defined for loading OBJ and MTL files. It's used by another new class  WFObj object for loading vertex data and texture data to the vertex and fragment shaders. Note that  a texture is not mandatory.

System  class diagram

WFObj derives from BaseGeometry class. It overrides mesh with an instance of WFObjMesh to generate geometry and material color information.

MaterialInfo

This class contains information about a single Material obtained after parsing a mtl file. This information includes  range of vertices, Ambient, Diffuse, Specular Colors and Texture information etc.  Note that a mtl file can have multiple Materials applicable to a range of vertices.

These are stored in WFObjMesh object discussed below.

Members

Name	Description
ambientclr	Contains ambient color
diffuseclr	Contains material information. It contains name of the material, mapped to the MatrialInfo structure.
diffusetxtfilename	Contains material file name associated with the obj file
emissiveclr	Contains normals
range	Contains texture info
shininess	Contains vertex info
specularclr	Contains Specular color

WFObjMesh 

WFObjMesh derives from IGeometryMesh class. It parses OBJ file and MTL files to provide geometry  and material color information for rendering. It supplies vertices, texture coordinates, normals, Ambient, Diffuse, Specular Colors and Texture information.

Members

Name	Description
faces	Contains vertex/texture coordinate/Normal information for each of the vertices of the geometry triangle.
matinfomap	Contains material information. It contains name of the material, mapped to the MatrialInfo structure.
mtlfilename	Contains material file name associated with the obj file
normals	Contains normals
texturemap	Contains texture info
vertices	Contains vertex info

Constructor

Parses obj and mtl files to generate geometry and color information.

Methods

Name	Description
GenerateVerticesData	This method generates vertex data for the GPU to render the geometrical shape. This method is called if the data is sent in  non indexed mode. It generates position and vertex data.
normals_count	This method returns number of normals.
texture_count	This method returns number of texture coordinates.
vertex_count	This method returns number of vertices.
readfile	This method reads obj file and mtl file and stores contents in text member
parsegeometrydata	This method generates geometry data from the obj file
parsematerialdata	This method generates material data from the mtl file

Light

This class contains light properties such as ambient Coefficient, light position, and light color.

These are stored in WFObjInfo object discussed below.

Members

Name	Description
ambientCoefficient	Contains ambient Coefficient. This is multiplied with ambient color of the material.
Position	Contains light position. Used in lighting calculations.
Color	Contains light color. Used in lighting calculations.

WFOBJInfo
This class contains information about Geometry information and Material color information obtained after parsing .obj and .mtl file.
These are stored in WFObj object discussed below.

Constructors
Creates a fully populated WFOBJInfo from the input parameters.

Members

Name	Description
objfilename	Contains name of the obj file
mtlfilename	Contains name of the mtl file
viewerpos	Contains texture info if a diffuse texture is available.
light	Contains an instance of Light object describing properties of the lighting.
texturemap	Contains texture info
vertices	Contains vertex info

WFObj

WFObj derives from BaseGeometry class. It renders objects after parsing obj and mtl files.

Members

Name	Description
hastexture	Contains true if the object has a diffuse texture file
shapeinf	Contains an instance of WFOBJInfo
texutl	Contains an instance of TextureUtil containing texture information if available.

Methods

Name	Description
Init	This method overrides the base class Init method to loads the WFOBJInfo object. It parses obj and mtl files to generate geometric and material information. Generates the vertices data and material data consisting of surface normals in non indexed mode and later sets them up in VBO buffer.  It also sets up initializes texutl to load texture if available.
UpdateUniforms	This method overrides the base class UpdateUniforms method. First it updates  "cameraposition" uniform. It updates "tex" uniform to pass texture object. Also Light and Material properties are passed to the shaders.
vertexShaderSource	This method overrides the base class vertexShaderSource method. It returns the vertex shader code to render the geometric object.
fragmentShaderSource	This method overrides the base class fragmentShaderSource method. It returns the fragment shader code to render the  geometric object.
UpdateUniformsLightMat	This method is called by UpdateUniforms() to update light and material properties to the shader.

Output