Draw

draw is built like print: it does not draw, it appends a command to the processor’s buffer. The picture appears when the buffer is handed to a display — that is drawflush’s job.

One instruction, and sixteen different commands behind it: fill the background, choose a colour, run a line, place a polygon, write text, move the origin. Their fields are shared and mean different things from command to command — hence one topic per lesson.

What we draw on

Block	Picture side	Space on the map
logic display	80 dots	3×3
large logic display	176 dots	6×6

A display’s dot is neither a map tile nor a screen pixel: the picture has a grid of its own, and its size is better asked of the block (sensor @displayWidth) than written as a number.

The origin is the bottom left corner, and the Y axis goes up. Not like a browser and not like the map editor, but like the game itself.

Lessons

1. The first pictureFour lines and a rectangle appears on the display. Without the last of them nothing appears at all
2. Shapes and linesThere are six shapes, and each asks for its own numbers: a corner here, a centre there, a radius elsewhere
3. Colour and transparencyColour is a state, not a property of a shape: choose it once and it holds until the next time
4. Text and picturesText reaches a display from the same buffer that feeds a message block — but not every letter survives the trip
5. Translate, rotate, scaleEasier than recomputing every point: move the grid itself and draw in it as if for the first time

What you need first

«The text buffer» — the same “pile up, then hand out” trick is built on it, and you need it to write anything on a display.