Rotate the Square - Demo 12

Purpose

Rotate the square around its origin.

Demo 12

Demo 12

How to Execute

On Linux or on MacOS, in a shell, type “python src/demo12/demo.py”. On Windows, in a command prompt, type “python src\demo12\demo.py”.

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/demo12/demo.py
193square_rotation: float = 0.0

When ‘q’ is pressed, increase the angle.

src/demo12/demo.py
198def handle_inputs() -> None:
199    global square_rotation
200    if glfw.get_key(window, glfw.KEY_Q) == glfw.PRESS:
201        square_rotation += 0.1

...

Event Loop

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

src/demo11/demo.py
268    glColor3f(0.0, 0.0, 1.0)
269    glBegin(GL_QUADS)
270    for model_space in square:
271        paddle1space: Vertex = model_space.translate(Vertex(x=2.0, y=0.0))
272        world_space: Vertex = paddle1space.rotate(paddle1.rotation) \
273                                          .translate(paddle1.position)
274        camera_space: Vertex = world_space.translate(translate_amount=-camera.position_worldspace)
275        ndc_space: Vertex = camera_space.uniform_scale(scalar=1.0/10.0)
276        glVertex2f(ndc_space.x, ndc_space.y)
277    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/demo12/demo.py
268    glColor3f(0.0, 0.0, 1.0)
269    glBegin(GL_QUADS)
270    for model_space in square:
271        paddle_1_space: Vertex = model_space.rotate(square_rotation) \
272                                            .translate(Vertex(x=2.0, y = 0.0))
273        world_space: Vertex = paddle_1_space.rotate(paddle1.rotation) \
274                                            .translate(paddle1.position)
275        camera_space: Vertex = world_space.translate(-camera.position_worldspace)
276        ndc_space: Vertex = camera_space.uniform_scale(scalar=1.0/10.0)
277        glVertex2f(ndc_space.x, ndc_space.y)
278    glEnd()

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