Week 9 Tutorial

Question 1: Texturing

1. What is a reason to use texture mapping rather than lots of little polygons? Are the two representations functionally equivalent? What are the differences?
2. What is difference between the following 2 texture filter settings?

   gl.glTexParameteri(GL.GL_TEXTURE_2D, GL.GL_TEXTURE_MAG_FILTER, GL.GL_NEAREST);
   

   gl.glTexParameteri(GL.GL_TEXTURE_2D, GL.GL_TEXTURE_MAG_FILTER, GL.GL_LINEAR);
   

3. What are Mip Maps? Why are they used?
4. What do the following settings do?

   float flargest[] = new float[];
   gl.glGetFloatv(GL.GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT, fLargest[0]);
   gl.glTexParameterf(GL.GL_TEXTURE_2D, GL.GL_TEXTURE_MAX_ANISOTROPY_EXT,fLargest[0]);
   

Question 2: Texture Co-ordinates

1. A quad with the following vertices, where you want to map the whole texture to the quad.

       gl.glVertex3d(-1, -1, -1.0);
       gl.glVertex3d(1, -1, -1.0);
       gl.glVertex3d(1, 1, -1.0);
       gl.glVertex3d(-1, 1, -1.0);
   

2. The same quad but where you want to map the whole texture to the quad in the y-direction, but have 3 repeated copies in the x direction. Assuming we are using GL2.GL_REPEAT mode.
3. The triangle

       gl.glVertex3d(-10.0, -10.0, 0.0);
       gl.glVertex3d(10.0, -10.0, 0.0);
       gl.glVertex3d(0.0, -5.0, 0.0);
   

4. The sides of a cylinder where the cylinder containing NUM_SLICES slices as specified below

    
       gl.glBegin(GL2.GL_QUAD_STRIP);{
       for(int i=0; i<= NUM_SLICES; i++){
           double angle = i*angleIncrement;
                           
           double xPos = Math.cos(angle);
           double yPos = Math.sin(angle);
                          
           gl.glNormal3d(xPos, yPos, 0);
                          
           gl.glVertex3d(xPos,yPos,zFront);
                           
           gl.glVertex3d(xPos,yPos,zBack);
   
       }
       }gl.glEnd();
   

5. The same cylinder but assuming we only want the texture to be like a label covering just one third of the curved surface.

Question 3: Vertex Buffer Objects and Texture Co-ordinates

private float vertices[] = { -10,0,0,
                              10,0,0,
                              10,10,0,
                              -10,10,0
                           };

private FloatBuffer vertexBuffer = Buffers.newDirectFloatBuffer(vertices);

public void init(GLAutoDrawable drawable) {
        GL2 gl = drawable.getGL().getGL2();
        //do init stuff
        //etc
   
        bufferIds = new int[1];
        gl.glGenBuffers(1,bufferIds,0);

        gl.glBufferData(GL.GL_ARRAY_BUFFER,vertices.length*4,vertexBuffer,GL2.GL_STATIC_DRAW);
}

public void display(GLAutoDrawable drawable) {
        GL2 gl = drawable.getGL().getGL2();
        //do display stuff
        //etc

       //draw the quad
}

1. What code would you have to add to the display function to draw the quad?
2. What would you have to modify/add to include texture co-ordinates in the VBO?

Question 4: Assignment