Filename: It is recommended that the filename has the extension pt4, i.e.
cool-image.pt4. (The "4" suggests the points are encoded in four bits). This
should reduce confusion with future versions.
Encoding: Everything is encoded as 4 bit nibbles and the presentation of values are also unsigned integers of 4 bits. The largest represented value is 15 and the smallest is 0.
Draw area: The draw width and height is 16 (a square), where the highest precision is one unit. This means that graphics are ultimately represented in a grid-like format.
Reccomendation: For images that are intended to be drawn small, it is recommended that they are designed with this in mind. For example, if your icon is to be displayed in a 4x4 window, design the icon in this resolution and upscale it to fill the draw window.
The shape selector byte tells the reader which type of shape is being drawn.
| Bit | Description |
|---|---|
| 7 | 0: Simple line sequence |
| 1: Curved line sequence | |
| 6 | 0: No fill |
| 1: Fill (assumes connected sequence) | |
| 5-4 | Reserved |
| 0-3 | Number of lines in the sequence, 16 maximum (starts from 1) |
A simple line sequence consists of (2 + NUM_LINES) bytes, the following example is for NUM_LINES = 2, no fill:
| Offset | Description |
|---|---|
| 0 | Shape selector, bits: [10000001] |
| 1 | (x1,y1) |
| 2 | (x2,y2) |
| 3 | (x3,y3) |
A curved line sequence consists of (2 + (2 x NUM_LINES)) bytes, the following example is for NUM_LINES = 3, with fill:
| Offset | Description |
|---|---|
| 0 | Shape selector, bits: [11000010] |
| 1 | (x1,y1) |
| 2 | (cx1,cy1) Centre of 1st curve |
| 3 | (x2,y2) |
| 4 | (cx2,cy2) Centre of 2nd curve |
| 5 | (x3,y3) |