Simplifying Computer Art

3D Drawing Options

1. Processing + Python

Processing

• created by Ben Fry and Casey Reas in 2001 from the MIT media lab
• integrated language + ide built on Java
• targeted at artists and beginners
• has a python mode

Processing + Python Code

angle = 0def setup():    size(640, 480, P3D)def draw():    global angle    clear()    translate(320, 240)    rotate(angle, 1, 1, 0)    fill(255, 0, 0)    box(100)    angle += PI/100.0

3D Drawing Options

1. Processing + Python
2. PyOpenGL

PyOpenGL

PyOpenGL is to OpenGL as PyQt is to Qt

pyOpenGL Code

from OpenGL.GL import *from OpenGL.GLUT import *from OpenGL.GLU import *

pyOpenGL Code

def InitGL(Width, Height):    glClearColor(0.0, 0.0, 0.0, 0.0)    glClearDepth(1.0)    glDepthFunc(GL_LESS)    glEnable(GL_DEPTH_TEST)    glShadeModel(GL_SMOOTH)    glMatrixMode(GL_PROJECTION)    glLoadIdentity()    gluPerspective(45.0, Width / Height, 0.1, 100.0)    glMatrixMode(GL_MODELVIEW)

pyOpenGL Code

def DrawGLScene():    global angle    glLoadIdentity()    glRotatef(angle, 1.0, 1.0, 0.0)    glBegin(GL_QUADS)    glColor3f(1.0, 0.0, 0.0)    glVertex3f(1.0, 1.0, -1.0)    glVertex3f(-1.0, 1.0, -1.0)    glVertex3f(-1.0, 1.0, 1.0)    glVertex3f(1.0, 1.0, 1.0)    ...    glEnd()    angle += 1

pyOpenGL Code

glutInit(sys.argv)glutInitDisplayMode(GLUT_RGBA | GLUT_DEPTH)glutInitWindowSize(Width, Height)glutCreateWindow()glutDisplayFunc(DrawGLScene)glutIdleFunc(DrawGLScene)InitGL(Width, Height)glutMainLoop()

3D Drawing Options

1. Processing + Python
2. PyOpenGL
3. pyglet

pyglet

Also a python OpenGL binding, but simplifies windowing and multimedia

pyglet

from pyglet.gl import *from pyglet import clock, window

pyglet

def update(dt):    global angle    angle += 1win = window.Window(height=Height, width=Width) pyglet.clock.schedule(update)clock.set_fps_limit(30)pyglet.app.run()

pyglet

@win.eventdef on_resize(width, height):    glClearColor(0.0, 0.0, 0.0, 0.0)    glClearDepth(1.0)    glEnable(GL_DEPTH_TEST)    glShadeModel(GL_SMOOTH)    glMatrixMode(GL_PROJECTION)    glLoadIdentity()    gluPerspective(45.0, Width / Height, 0.1, 100.0)    glMatrixMode(GL_MODELVIEW)    return pyglet.event.EVENT_HANDLED

pyglet

@win.eventdef on_draw():    global angle    glLoadIdentity()    glTranslatef(0.0, 0.0, -6.0)    glRotatef(angle, 1, 1, 0)    glBegin(GL_QUADS)    glColor3f(1.0, 0.0, 0.0)    glVertex3f(1.0, 1.0, -1.0)    glVertex3f(-1.0, 1.0, -1.0)    glVertex3f(-1.0, 1.0, 1.0)    glVertex3f(1.0, 1.0, 1.0)    ...

3D Drawing Options

1. Processing + Python
2. PyOpenGL
3. pyglet
4. VPython

VPython

• Created by David Scherer in 2000 to replace cT, a simple graphics library used in CMU’s computational physics classes
• Further development led by Bruce Sherwood, a developer of cT
• Developed to aid understanding of physics through computing
• C++ calls OpenGL, compiled to a module called cvisual
• depends on wxPython and boost

physics example: projectile motion

ball = sphere(pos=vector(-10, 0, 0), radius=0.1,               color=color.red, make_trail=True)ball.velocity = vector(10, 10, 0)time = 0.0; time_final = 2; dt = 0.01; m = 0.15while time <= time_final and ball.pos.y > -0.1:    rate(100)    f = - m * vector(0, 9.8, 0)        ball.pos += ball.velocity * dt    ball.velocity += f * dt / m    time += dt

physics example: projectile motion with air resistance

ball = sphere(pos=vector(-10, 0, 0), radius=0.1,               color=color.red, make_trail=True)ball.velocity = vector(10, 10, 0)time = 0.0; time_final = 2; dt = 0.01; m = 0.15while time <= time_final and ball.pos.y > -0.1:    rate(100)    f = - m * vector(0, 9.8, 0)          -0.006 * ball.velocity * ball.velocity.mag    ball.pos += ball.velocity * dt    ball.velocity += f * dt / m    time += dt

VPython code

from visual import *a_box = box(width=1, height=1, length=1, color=color.red)while True:    rate(10)    a_box.rotate(angle=radians(1), axis=vector(1, 1, 0))

An OpenGL Helper

• Use the C++ code from VPython as a guide
• Let a python OpenGL binding do the heavy lifting
• Obscure the windowing

PyOpenGL vs. pyglet

Why pyglet?

• Better documentation
• Extra app, window, sound, image and video libraries

A Helper for Pyglet

• Submodule “objects” has geometric shape primitives
• Submodule “utils” has mathematical primitives (vector, vertex, etc)
• Let pyglet.gl interact with OpenGL
• Let pyglet.window and pyglet.app handle display

Multiple Method Declarations

explicit vector( double a = 0.0, double b = 0.0,                 double c = 0.0) throw()	: x(a), y(b), z(c) {}inline explicit vector( const double* v)	: x(v[0]), y(v[1]), z(v[2]) {}

Python version

def __init__(self, in_vector=None):    if in_vector is None:        self.zero()    elif len(in_vector) > 2:        for i in range(len(self)):            self[i] = in_vector[i]    else:        raise ValueError("in_vector must contain "                         "at least three numbers!")

Use Continuous Integration!

• Runs setup.py install for python 2.7 - 3.4
• Runs pylint to check for PEP8
• Runs unit tests

Continous integration with no display

OpenGL requires a display to draw to, but Travis-CI runs on a headless server!

Rendering to a still image

• Xdummy appears to require the Nvidia X driver.
• Nvidia X driver does not work on headless systems.
• If you know a solution, let me know!

Alternative - Mocking GL

@patch('pyglet_helper.objects.box.gl',       new=pyglet_helper.test.fake_gl)def test_box_generate_model():    from pyglet_helper.objects import Box    box = Box()    box.generate_model()

fake_gl module

def glVertex3f(x_component, y_component, z_component):    pass

pyglet_helper Functionality

1. Objects
2. Lights and scenes
3. Default scene

Lights and Scenes

• The Scene object contains information on the camera position
• Lights are non-renderable objects
• Objects can either be drawn in a scene by passing the scene as an argument, or by adding the object to a scene and rendering a scene

Drawing options

my_box = Box()my_scene = View()my_box.render(my_scene)

or

my_scene.objects.append(my_box)my_scene.setup()    

Default Scene

from pyglet_helper import *vsetup()box = objects.Box(size=(1, 1, 1), color=util.RED)def update(dt):    box.rotate(angle=radians(1),               axis=util.Vector([1, 1, 0]))vrun(update, render_images=True, max_frames=180)

vpython ecosystem

1. Sherwood and others switched efforts from OpenGL to WebGL
   1. wxPython has no python 3 version
   2. few people familiar with C++ code base
2. GlowScript JavaScript library written in 2012
3. Two python routes to GlowScript

glowscript.org

1. completely online, no local installs
2. Python-to-JavaScript transpiler provides python interface
3. no access to full scientific Python stack

vpython-jupyter

1. Originally developed by John Coady as ivisual
2. Updated to use GlowScipt Python API and released on PyPI as vpython
3. Runs in Jupyter notebook, typically in a local installation
4. Rendering handled through a comm channel to GlowScipt loaded in the front end

Future Work on pyglet_helper

1. undo the styling changes so that it matches the textbook formats
2. 3D Text
3. Switch to PyOpenGL

Python version

from vispy import app, scenefrom vispy.visuals import transforms   canvas = scene.SceneCanvas(keys='interactive')view = canvas.central_widget.add_view()def update(dt):    global cube    cube.transform.rotate(1, (1, 1, 0))cube = scene.visuals.Cube(color='red', edge_color="k")cube.transform = transforms.MatrixTransform()view.add(cube)view.camera = scene.TurntableCamera()canvas.show()timer = app.Timer('auto', connect=update, start=True)canvas.app.run()

An Experiment