HALF_PI

A number constant that's approximately 1.5708.

HALF_PI is the mathematical constant π/2. It's useful for many tasks that involve rotation and oscillation. For example, calling rotate(HALF_PI) rotates the coordinate system HALF_PI radians, which is a quarter turn (90 degrees).

Note: TWO_PI radians equals 360 degrees, PI radians equals 180 degrees, HALF_PI radians equals 90 degrees.

Examples

HALF_PI example 1

function setup()
  size(100, 100)

  background(200)

  -- Draw an arc from 0 to HALF_PI.
  arc(50, 50, 80, 80, 0, HALF_PI)

  describe('The bottom-right quarter of a circle drawn in white on a gray background.')
end

HALF_PI example 2

function setup()
  size(100, 100)

  background(200)

  -- Translate the origin to the center.
  translate(50, 50)

  -- Draw a line.
  line(0, 0, 40, 0)

  -- Rotate a quarter turn.
  rotate(HALF_PI)

  -- Draw the same line, rotated.
  line(0, 0, 40, 0)

  describe('Two black lines on a gray background. One line extends from the center to the right. The other line extends from the center to the bottom.')
end

HALF_PI example 3

function setup()
  size(100, 100)

  describe(
    'A red circle and a blue circle oscillate from left to right on a gray background. The red circle appears to chase the blue circle.'
  )
end

function draw()
  background(200)

  -- Translate the origin to the center.
  translate(50, 50)

  -- Calculate the x-coordinates.
  local x1 = 40 * sin(frameCount * 0.05)
  local x2 = 40 * sin(frameCount * 0.05 + HALF_PI)

  -- Style the oscillators.
  noStroke()

  -- Draw the red oscillator.
  fill(255, 0, 0)
  circle(x1, 0, 20)

  -- Draw the blue oscillator.
  fill(0, 0, 255)
  circle(x2, 0, 20)
end

This reference page contains content adapted from p5.js and Processing by p5.js Contributors and Processing Foundation, licensed under CC BY-NC-SA 4.0.

HALF_PI

Examples

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