Rotate the Square - Demo 12¶

Objective¶

Rotate the square around its origin.

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¶

Code¶

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

src/modelviewprojection/demo12.py¶

square_rotation: float = 0.0

When ‘q’ is pressed, increase the angle.

src/modelviewprojection/demo12.py¶

def handle_inputs() -> None:
    global square_rotation
    if glfw.get_key(window, glfw.KEY_Q) == glfw.PRESS:
        square_rotation += 0.1

...

Event Loop¶

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

src/modelviewprojection/demo11.py¶

    GL.glColor3f(0.0, 0.0, 1.0)
    GL.glBegin(GL.GL_QUADS)
    for ms in square:
        ms_to_ndc: mu.InvertibleFunction[mu2d.Vector2D] = mu.compose(
            [
                # camera space to NDC
                mu.uniform_scale(1.0 / 10.0),
                # world space to camera space
                mu.inverse(mu.translate(camera.position_ws)),
                # model space to world space
                mu.compose(
                    [
                        mu.translate(paddle1.position),
                        mu2d.rotate(paddle1.rotation),
                    ]
                ),
                # square space to paddle 1 space
                mu.translate(mu2d.Vector2D(x=2.0, y=0.0)),
            ]
        )
        square_vector_ndc: mu2d.Vector2D = ms_to_ndc(ms)
        GL.glVertex2f(square_vector_ndc.x, square_vector_ndc.y)
    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¶

    GL.glColor3f(0.0, 0.0, 1.0)
    GL.glBegin(GL.GL_QUADS)
    for ms in square:
        ms_to_ndc: mu.InvertibleFunction[mu2d.Vector2D] = mu.compose(
            [
                # camera space to NDC
                mu.uniform_scale(1.0 / 10.0),
                # world space to camera space
                mu.inverse(mu.translate(camera.position_ws)),
                # model space to world space
                mu.compose(
                    [
                        mu.translate(paddle1.position),
                        mu2d.rotate(paddle1.rotation),
                    ]
                ),
                # square space to paddle 1 space
                mu.compose(
                    [
                        mu.translate(mu2d.Vector2D(x=2.0, y=0.0)),
                        mu2d.rotate(square_rotation),
                    ]
                ),
            ]
        )
        square_vector_ndc: mu2d.Vector2D = ms_to_ndc(ms)
        GL.glVertex2f(square_vector_ndc.x, square_vector_ndc.y)
    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.