Lecture 3/4

OpenGL: Texture Mapping

Download.

Please download gl1.cpp for today's lecture. I have written Canvas :: ReadPPM(), which is used to read in any ppm image file for use with our open GL applications. Go to Canvas.cpp, copy ReadPPM() to your Canvas class.

I have also re-generated sphere triangulation data, so now all the five obj files having texture data. Download sphere1.obj, sphere2.obj, sphere3.obj, sphere4.obj, sphere5.obj.

If you want to generate a realistic looking earth, you need to download this image.

Programming

• Steps for texture mapping

  • Create texture object(s)

       GLuint texName[2];            // replace 2 (in the next line too) with the actual number of texture objects you want to create.
       glGenTextures(2, texName);
    

  • Initialize each texture object

       glBindTexture(GL_TEXTURE_2D, texName[0]);                     // or texName[1] to initialize the second texture object just created above.
       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);  // clamping if s texture val out range of [0,1]. The other common choise is GL_REPEAT.
       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);  // clamping if t texture val out range of [0,1]. The other common choise is GL_REPEAT.
    
       /* these are anti-aliasing related issue, you dont have to understand .*/
       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, 
                       GL_NEAREST);
       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, 
                       GL_NEAREST);
    
       /*
          Now bind the actual image to be texture mapped for this texture object
          There are a few important things you have to be VERY careful,
             1. you must pass the correct data type of the color component in your image.
             2. the image size must be 2^m + b and >= 64, where ususally b = 0 as below,
       */
       glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, checkImageWidth,
                    checkImageHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE,
                    checkImage);
    

  • In you display() callback: Bind geometry to texture object, and bind vertexes to texture coordinates

       glBindTexture(GL_TEXTURE_2D, texName[0]);
       glBegin(...);
       ...
       glTexCoord2f(s, t); 
       glVertex3f(x, y, z);             // this vertex is related to the texture coordinate (s,t) just given.
    
       glEnd();
    

• Create checkerboard image and map to a quad

• Use Canvas class to read in any ppm file and map to a quad

• Use a small image to repeatedly cover a quad

• Texture mapping combined with lighting

• Texture mapping to a sphere

• Change TriangleMesh :: glDraw() to support texture mapping

Homework

Render a TriangleMesh model with any texture mapping, and lighting computation enabled. Submit your source code and image to zh2001 AT columbia DOT edu, and cc copy to xchen AT cs DOT utah DOT edu, before 7pm Monday.

---