Ruby OpenGL Walk Bounce

Pretty bouncing effect that gives an illusion that you are walking forward

Normally we would move the camera around and draw the 3D environment relative to the camera position. Here is a trick on how to do it very inexpensively.

1. Rotate and translate the camera position according to user commands
2. Rotate the world around the origin in the opposite direction of the camera rotation (giving the illusion that the camera has been rotated)

3. Translate the world in the opposite manner that the camera has been translated (again, giving the illusion that the camera has moved)

   def update
     @ang_conv = 0.0174532925 # pi / 180
     @y_ang -= 1.5 if button? Button::KbRight
     @y_ang += 1.5 if button? Button::KbLeft
   
     if button?(Button::KbUp)
       @x_pos -= Math.sin(@y_ang * @ang_conv) * 0.05
       @z_diff -= Math.cos(@y_ang * @ang_conv) * 0.05
       @bounce_ang > 359 ? @bounce_ang = 0 : @bounce_ang += 10
       @bouncing = Math.sin(@bounce_ang * @ang_conv) / 20
     end
   
     if button?(Button::KbDown)
       @x_pos += Math.sin(@y_ang * @ang_conv) * 0.05
       @z_diff += Math.cos(@y_ang * @ang_conv) * 0.05
       @bounce_ang <= 1 ? @bounce_ang = 359 : @bounce_ang -= 10
       @bouncing = Math.sin(@bounce_ang * @ang_conv) / 20
     end
   
     @z_diff -= 0.3 if button? Button::KbPageUp
     @z_diff += 0.3 if button? Button::KbPageDown
   
     @y_pos -= 0.05 if button? Button::KbW
     @y_pos += 0.05 if button? Button::KbS
     @x_pos += 0.05 if button? Button::KbD
     @x_pos -= 0.05 if button? Button::KbA
   end
   
   def draw
     x = -@x_pos
     y = -@bouncing - 0.25
     z = -@z_diff
     scene_angle = 360 - @y_ang
     gl 
       glRotatef(@z_diff,1,0,0) #rotate to be able to look up or down
       glRotatef(scene_angle,0,1,0); #rotate on direction user is facing
       glTranslate(x, y, z) #translate the world in opposite of camera
     end
   end