Copy the *.cpp (3 files) and the *.h (2 files) and the Makefile into your own box directory.

Make the files.

Play with OpenGL.

• Change the shape from a square to a triangle.




• Change the GL_POLYGON to GL_LINE_LOOP/GL_LINES/GL_LINE_STRIP/etc
  
  • Remember a polygon should ideally be either a triangle or a quad.
  • Polygons should ALWAYS be planar. This means triangles are usually the best choice. Find out what happens if you draw a non-planer polygon (using 4 vertices).
  • Polygons can model flat, planar surfaces well, but are merely are an approximation to a curved surface. (Think of drawing a circle with a number of very small straight lines).
  
  
• Change the colours of the lines/sides/vertices. Use the glColor*() routine.
  
  • Colours are specified using the RGBA scheme: red; green; blue; alpha (for blending and transparency). We will talk about the alpha value in later labs.
  • Example: glColor3f(0.0, 0.0, 0.0); glColor3f(r, g, b); red = 0, blue = 0, green = 0. Therefore colour = black.
  • Colour values range from (0.0 -> 1.0). If you try a number above 1.0 the value will be clamped to 1.0. As with light, glColor3f(1.0, 1.0, 1.0) is white.
  • Try making each corner a different colour. Hint: OpenGL expects you to set a colour and from then on uses that colour until another colour is set.
  • What happens when you change the value of glShadeModel(GL_SMOOTH) to glShadeModel(GL_FLAT)?
  
  
  
• In the code that defines the object and its position use multiple transformations (translation, rotation and scale), observe the effects these have on the object. And the effect of their order. Is the order of concatination of transformations commutative?
  
  
  
  • Try drawing 2 of the same polygons on the screen at once, in the same place, ie with the same co-ordinates.
  • Use different translation and scales on each polygon to see the effect.
    (Hint: Before the glBegin(GL_POLYGON); line put a glTranslatef(x, y, z); and glScalef(x, y, z); Note: x, y, and z are all floats; remember if you make them too large the object may disappear out of view.)
  • Translate the second triangle. eg, glTranslatef(-1.0, -1.0, 0.0); before the glBegin(GL_POLYGON);
    
    
    
  • Scale the second triangle. eg glScalef(1.5, 2.0, 1.0); before the above glTranslatef()
    
    
    
  • Rotations are different. glRotatef(rot, x, y, z);
    
    
    • you use rot to specify the angle of rotation you want.
    • use 1.0 to specify the axes you want to rotate on (in an anti-clockwise direction).
    • eg: glRotatef(20, 1.0, 0.0, 0.0); rotates 20 degrees on the x-axis
      glRotatef(20, 0.0, 1.0, 0.0); rotates 20 degrees on the y-axis
      glRotatef(20, 0.0, 0.0, 1.0); rotates 20 degrees on the z-axis