OpenGL 3D and Animation for Simulating a Solar System

1
OpenGL 3D and AnimationforSimulating a Solar
System

• Assignment 3
• CMPS 160

2
Demo

• My code is in 3 files main.cc systems.h
  systems.cc
• 364 lines of non-base code
• I have multiple systems of planets and moons (you
  only need 1 planet and 1 moon to get credit)

3
New Concepts

• 3 dimensional world
• Complex hidden state
• Full screen animation
• Multiple frames of reference
• Camera vs Object Motion
• How do these changes affect my design compared to
  the 2D painting program?

4
3D World

• 3 parameters (x,y,z), duh - glVertex3f()
• Using perspective projection instead of
  orthographic - gluPerspective()
• Objects can occlude (block visibility) one
  another, we need a depth buffer to figure out
  when this is happening - glutInitDisplayMode()
  with GLUT_DEPTH, glEnable(GL_DEPTH_TEST),
  glClear(..) with GL_DEPTH_BUFFER_BIT

5
Complex Hidden State

• For a simple sun, earth, moon simulation we need
  to track
• Sun
• earths orbital rotation state
• Earth
• earths axial rotation state
• moons orbital rotation state
• Moon
• moons axial rotation state
• AND on top of that we need up update this state
  using some constants for the rate of each
  rotation and the amount of time that has passed
  before we draw the scene each time!

6
Full Screen Animation

• In painting assignment we only drew one picture.
  This program should draw new pictures over and
  over as fast as it can.
• All painting goes in the display callback
• Add an idle callback that tells GLUT to git
  drawin again - glutPostRedisplay()
• We dont want the user to watch us drawing so we
  draw to a back buffer while user looks at front,
  then swap them when we are ready to show them the
  new picture - glutSwapBuffers() -- implicitly
  flushes
• We want to take up the whole screen -- use
  glutFullScreen() after glutCreateWindow()

7
Multiple Frames of Reference(the important part
of this assignment)

• Earth rotates around the sun
• Earth rotates around its own axis
• The Moon rotates around Earth
• The Moon rotates around its own axis
• OpenGL does all of the hard math for you as long
  as you tell it what frame you want to work in -
  glTranslate, glRotate, glPushMatrix, glPopMatrix,
  glScale
• Ideally, you can do the whole assignment without
  sin() and cos()

8
Camera vs Object Motion

• OpenGL doesnt make a distinction here, but you
  should.
• Scene is rendered from eyes frame of reference.
• Simulation is run from the suns frame of
  reference.
• Use gluLookAt() or other functions to move the
  simulated worlds origin with respect to the eye
  before drawing the world. This has same logical
  effect as moving the eye within the world.

9
Camera Setup

• In your reshape callback reset the projection
  matrix to be a perspective projection with the
  appropriate aspect ratio, nothing more.
• In your display callback, the first thing change
  to the modelview matrix should be the cameras
  transformation (with gluLook at), after that
  everything (the solar system) you draw will be
  relative to the shifted origin so it looks
  correct from the eye point. Save the modelview
  matrix anytime you think youll need its state
  back later.

10
Complex Hierarchical Drawing Using the Current
State Variables(easier viewing on your own
computer)
arm_length

• glPushMatrix()
• drawTower(tower_height)
• glTranslate(0,tower_height,0)
• glRotate(arm_angle,1,0,0)
• drawControlBox()
• drawArm(arm_length)
• glTranslate(0,0,arm_length)
• glPushMatrix()
• glRotate(pulley_angle,0,1,0)
• drawPulley()
• glPopMatrix()
• glTranslate(-cable_length,0,0)
• drawBarrel()
• glPopMatrix()
• glPushMatrix()
• glTranslate(first_barrel,0,0)
• for(I0 Ilt4 I)
• drawBarrel()

pulley_angle
arm_angle
cable_length
tower_height
firsrt_barrel
barrel_spacing
11
I still dont really feel like I understand
OpenGL in general

• At other schools there are whole classes on
  OpenGL or at least a few lecture sessions about
  it
• cmps160 is more concept-based, you only learn to
  program with OpenGL in the lab.
• I learned OpenGL myself from examples and
  documentation. However, if you learn best
  through colorful PowerPoint? presentations, here
  is a good starter covering everything up through
  this assignment http//www.cs.virginia.edu/gfx/C
  ourses/2004/Intro.Spring.04/Lectures/lecture04.ppt
  

12
Base Code

• You write main.cc from scratch this time
  (really!). Copying the old main.cc is fine, but
  youll still have to make some major changes to
  the contents of your callbacks.
• We provide two functions (in helper.h) to make
  your solar system pretty if you desire
• helperSetupLighting() -- call this in main after
  you have registered the callbacks
• helperPlaceLight() -- call this when you are
  drawing the scene in the display callback --
  places the suns lighting at the current origin