Sixty years after Sketchpad, the gesture is unchanged: a stylus, a surface, and a machine turning the movement into geometry it can store.
Credit line sits here
Mechanism
Four problems that never went away
Each one was created by the grid, and each one was answered by somebody whose name is on the entry.
01
Which pixels a line lands on
A straight line rarely agrees with the grid, so an algorithm has to decide which pixels it lands on using only integers.
02
How a smooth path is stated
Pierre Bézier published the curve for car bodywork, and it survives because four points describe a smooth path that is easy to compute and easy to drag.
03
Why an edge has a stair on it
A hard edge on a grid produces a stair, and softening the boundary trades one artefact for a less objectionable one.
04
Two ways to make a colour
One adds light and the other subtracts it, and neither can describe the whole of what the other can.
Supported by
Printers, foundries and labs who keep this going
Raster
Drawing
The same file, twice
A screen adds light. A press takes it away.
Colour · 04.1
Emitted · RGB
Printed · CMYK
Plot both on the diagram the Commission internationale de l'éclairage agreed in 1931 and neither shape contains the other. A conversion between them is a decision about what to lose.
Six of 21
From the register
Every entry is one problem the grid created and somebody solved.
- Raster The framebuffer Giving every pixel an address
- Drawing Constraints Stating what a drawing must be
- Curves de Casteljau Evaluating a curve by subdivision
- Colour CIE 1931 A map of what the eye responds to
- Instruments The RAND Tablet Reading a stylus position directly
- Raster SuperPaint Painting straight into memory
Six ways in
The sections
The grid, and living with it.
Making marks interactively.
Smooth shapes from a handful of numbers.
Measuring something the eye does.
What the hand actually holds.
All 21 entries in one table, with the section and the problem each one solved.
Curves
Colour and instruments
