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
134square_rotation: float = 0.0

When ‘q’ is pressed, increase the angle.

src/modelviewprojection/demo12.py
139def handle_inputs() -> None:
140    global square_rotation
141    if glfw.get_key(window, glfw.KEY_Q) == glfw.PRESS:
142        square_rotation += 0.1

...

Event Loop

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

src/modelviewprojection/demo11.py
222    GL.glColor3f(0.0, 0.0, 1.0)
223    GL.glBegin(GL.GL_QUADS)
224    for ms in square:
225        ms_to_ndc: mu2d.InvertibleFunction = mu2d.compose(
226            [
227                # camera space to NDC
228                mu2d.uniform_scale(1.0 / 10.0),
229                # world space to camera space
230                mu2d.inverse(mu2d.translate(camera.position_ws)),
231                # model space to world space
232                mu2d.compose(
233                    [
234                        mu2d.translate(paddle1.position),
235                        mu2d.rotate(paddle1.rotation),
236                    ]
237                ),
238                # square space to paddle 1 space
239                mu2d.translate(mu2d.Vector2D(x=2.0, y=0.0)),
240            ]
241        )
242        square_vector_ndc: mu2d.Vector2D = ms_to_ndc(ms)
243        GL.glVertex2f(square_vector_ndc.x, square_vector_ndc.y)
244    GL.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
224    GL.glColor3f(0.0, 0.0, 1.0)
225    GL.glBegin(GL.GL_QUADS)
226    for ms in square:
227        ms_to_ndc: mu2d.InvertibleFunction = mu2d.compose(
228            [
229                # camera space to NDC
230                mu2d.uniform_scale(1.0 / 10.0),
231                # world space to camera space
232                mu2d.inverse(mu2d.translate(camera.position_ws)),
233                # model space to world space
234                mu2d.compose(
235                    [
236                        mu2d.translate(paddle1.position),
237                        mu2d.rotate(paddle1.rotation),
238                    ]
239                ),
240                # square space to paddle 1 space
241                mu2d.compose(
242                    [
243                        mu2d.translate(mu2d.Vector2D(x=2.0, y=0.0)),
244                        mu2d.rotate(square_rotation),
245                    ]
246                ),
247            ]
248        )
249        square_vector_ndc: mu2d.Vector2D = ms_to_ndc(ms)
250        GL.glVertex2f(square_vector_ndc.x, square_vector_ndc.y)
251    GL.glEnd()

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