Lesson 09a: Importing WaveFront OBJ Models using AssetImpParser

Overview 

As discussed in the  previous article, we saw how geometric objects can be imported from obj and mtl files. Also, the implementation of the GenericObjMesh, GenericObj and GenericParser were covered. 

In this post we will try to render a model from "dolphin.obj" and "dolphin.mtl" files.

Details

The purpose of  Lesson09 is to demonstrate importing an obj and mtl files to extract geometry and material information.

System  class diagram

The scene class overrides camera with an instance of ThreeDCamera. 

Implementation

Scene

The functionality is implemented in the Scene class derived from BaseScene class. It creates an instance of AssetImpParser which parses the OBJ file and generates 1 more MeshInfo objects, MaterialInfo objects, TextureInfo Objects. 

Each MeshInfo is associated with a MaterialInfo and 0 or 1 TextureInfo Object along with Vertex data. Each MeshInfo  is represented by an instance of GenericObj instance which later becomes 

The three methods Init, DrawScene and Cleanup are overridden as below:

The Init method calls 

1. BaseScene::Init to create hosting window and OpenGL Context. 
2. It creates an input dialog to import obj, and mtl files and input texture files.
3. It calls init function with an instance of  GenericObj object. Internally it creates a GenericObj Mesh object to load geometry and material information from the object files and to populate VBO/EBO buffers and bind them. Also create texture if necessary 
4. It also compiles and links shader programs.

The DrawScene method draws a string and image. 

The message handler for IDOK is called when Apply button is pressed after updates are made in the input dialog. It refreshes the display.

The message handler for IDCANCEL is called when in Cancel button is pressed the input dialog. It calls 

OnCloseWindow to destroy window.

Finally the WM_CLOSE  event is  handled in OnCloseWindow function and the window is destroyed and  application is shutdown when the window is closed or Escape key is pressed. 

Application

Scene class is hosted main.cpp. which creates the scene object and displays it. Message pump is added to process windows messages.

Input dialog

The input dialog as shown below can be used to change settings and understand drawing text and images.

Output

The output looks as shown in the top.