Rotate the Square - Demo 12

Purpose

Rotate the square around its origin.

Demo 12

Demo 12

How to Execute

Load src/demo12/demo.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/demo12/demo.py
196square_rotation: float = 0.0

When ‘q’ is pressed, increase the angle.

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

...

Event Loop

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

src/demo11/demo.py
269    glColor3f(0.0, 0.0, 1.0)
270    glBegin(GL_QUADS)
271    for model_space in square:
272        paddle1space: Vertex = model_space.translate(Vertex(x=2.0, y=0.0))
273        world_space: Vertex = paddle1space.rotate(paddle1.rotation).translate(
274            paddle1.position
275        )
276        camera_space: Vertex = world_space.translate(-camera.position_ws)
277        ndc: Vertex = camera_space.uniform_scale(scalar=1.0 / 10.0)
278        glVertex2f(ndc.x, ndc.y)
279    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
272    glColor3f(0.0, 0.0, 1.0)
273    glBegin(GL_QUADS)
274    for square_vertex_ms in square:
275        paddle_1_space: Vertex = square_vertex_ms.rotate(square_rotation).translate(
276            Vertex(x=2.0, y=0.0)
277        )
278        world_space: Vertex = paddle_1_space.rotate(paddle1.rotation).translate(
279            paddle1.position
280        )
281        camera_space: Vertex = world_space.translate(-camera.position_ws)
282        ndc: Vertex = camera_space.uniform_scale(scalar=1.0 / 10.0)
283        glVertex2f(ndc.x, ndc.y)
284    glEnd()

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