Rotate the Square - Demo 12

Objective

Rotate the square around its origin.

Demo 12

Demo 12

How to Execute

Load src/modelviewprojection/demo12.py in Spyder and hit the play button.

Move the Paddles using the Keyboard

Keyboard Input

Action

w

Move Left Paddle Up

s

Move Left Paddle Down

k

Move Right Paddle Down

i

Move Right Paddle Up

d

Increase Left Paddle’s Rotation

a

Decrease Left Paddle’s Rotation

l

Increase Right Paddle’s Rotation

j

Decrease Right Paddle’s Rotation

UP

Move the camera up, moving the objects down

DOWN

Move the camera down, moving the objects up

LEFT

Move the camera left, moving the objects right

RIGHT

Move the camera right, moving the objects left

q

Rotate the square around its center

Description

Cayley Graph

Demo 12

Demo 12

Code

Make a variable to determine the angle that the square will be rotated.

src/modelviewprojection/demo12.py
163square_rotation: float = 0.0

When ‘q’ is pressed, increase the angle.

src/modelviewprojection/demo12.py
168def handle_inputs() -> None:
169    global square_rotation
170    if glfw.get_key(window, glfw.KEY_Q) == glfw.PRESS:
171        square_rotation += 0.1

...

Event Loop

In the previous chapter, this was the rendering code for the square.

src/modelviewprojection/demo11.py
244    glColor3f(0.0, 0.0, 1.0)
245    glBegin(GL_QUADS)
246    for ms in square:
247        ms_to_ndc: InvertibleFunction[Vector2D] = compose(
248            # camera space to NDC
249            uniform_scale(1.0 / 10.0),
250            # world space to camera space
251            inverse(translate(camera.position_ws)),
252            # model space to world space
253            compose(translate(paddle1.position),
254                    rotate(paddle1.rotation)),
255            # square space to paddle 1 space
256            translate(Vector2D(x=2.0,
257                               y=0.0)))
258        square_vector_ndc: Vector2D = ms_to_ndc(ms)
259        glVertex2f(square_vector_ndc.x, square_vector_ndc.y)
260    glEnd()

Since we just want to add one rotation at the end of the sequence of transformations from paddle 1 space to square space, just add a rotate call at the top.

src/modelviewprojection/demo12.py
250    glColor3f(0.0, 0.0, 1.0)
251    glBegin(GL_QUADS)
252    for ms in square:
253        ms_to_ndc: InvertibleFunction[Vector2D] = compose(
254            # camera space to NDC
255            uniform_scale(1.0 / 10.0),
256            # world space to camera space
257            inverse(translate(camera.position_ws)),
258            # model space to world space
259            compose(translate(paddle1.position),
260                    rotate(paddle1.rotation)),
261            # square space to paddle 1 space
262            compose(translate(Vector2D(x=2.0,
263                                       y=0.0)),
264                    rotate(square_rotation)))
265        square_vector_ndc: Vector2D = ms_to_ndc(ms)
266        glVertex2f(square_vector_ndc.x, square_vector_ndc.y)
267    glEnd()

The author is getting really tired of having to look at all the different transformation functions repeatedly defined for each object being drawn.