Bhaumik’s room

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jamz

Childhood photo of Bhaumik at a desktop computer

A luminous red and yellow sun over an ocean with a lone figure

untitled — Paint

Brushes 15

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rakegraphite

Write your own brush

The engine springs a virtual brush toward the cursor each frame. That lag is what makes the curves silky, and it is also where speed comes from. Every frame it hands the brush one short segment and asks it to draw. A brush is just seg(s), plus optional start and end.

Draw into s.g. Keep per-stroke state on s.mem. Call stamps(s, gap, fn) to place marks at a fixed spacing along the path whatever the frame rate — that is how bead, halftone and stitch stay even.

Field	What it is
s.x, s.y	brush position now
s.px, s.py	where it was last frame
s.tx, s.ty	unit tangent — direction of travel
s.nx, s.ny	unit normal — 90° off the tangent
s.pnx, s.pny	last frame's normal (use it to avoid kinks)
s.speed	smoothed px per frame — the pressure signal
s.len	total path length so far
s.size, s.col	slider size, hex pigment
s.mem	scratch object, fresh per stroke

Add one to apps/paint/brushes.js:

// a comet: solid head, particles shedding behind it
brush({
  id: 'comet', name: 'comet', kind: 'new',
  note: 'head sized by speed, sparks shed off the tail',

  start(s) { s.mem.heat = 0 },

  seg(s) {
    const g = s.g
    // fast strokes burn hotter and shed more
    const v = E.map(s.speed, 1, 26, 0, 1, true)
    s.mem.heat += (v - s.mem.heat) * 0.2

    g.noStroke()
    g.fill(s.col)
    g.circle(s.x, s.y, s.size * (0.34 - s.mem.heat * 0.18))

    // one spark every few px, flung back along -tangent
    E.stamps(s, s.size * 0.3, (x, y) => {
      const k = 1 + Math.random() * 5 * s.mem.heat
      g.circle(
        x - s.tx * s.size * k * 0.4 + s.nx * (Math.random() - 0.5) * s.size * k,
        y - s.ty * s.size * k * 0.4 + s.ny * (Math.random() - 0.5) * s.size * k,
        s.size * 0.09 * Math.random()
      )
    })
  },

  end(s) {
    // a last bright dot where the hand stopped
    s.g.circle(s.x, s.y, s.size * 0.42)
  },
})

Table of Contents

Fall Semester ’26

Dear Bhaumik,

Studies

My Pictures

Open website