> You select the "draw tube" brush and then draw! Holding down the mouse
> button and moving up draws verical tubes.......you turn right and a "L tube
> piece" is made, then vertical tubes follow. If you cross over any vertical or
> horizontal tube whilst drawing then a cross section is made, likewise for
> any T junctions. Think of it like drawing with toothpaste
This would be the perfect and intuitive way to draw tubes!
> As Holger said, it would be useful indeed, but hardly to realise!
Not necessarily.
> And as LieDetector said, when crossing two "pipe-lines" it would be really
> hard to realise as well because the tool woul have to know, which direction
> is wanted.
That's true. But I have found out that it's relatively easy to add a little hook to the standard drawing tools to add such "intuitive" or "magic" drawing possibilities, which are quite useful for complex objects like tubes and acid pools!
I nearly forgot that I already implemented this a short time after reading the first post in this thread -- here is how it works (in 3.2.4). (I have called this "IntelliDraw" internally, although this name is most probably already patented and I will be sued to death if somebody reads this -- so don't tell anybody. ;-) )
Let's start with tubes:































































This figure was drawn with one single mouse click! (That means, pressing the mouse button, moving the mouse around and finally releasing the mouse button again.)
To do this, just select *any* tube element, select the "single items" drawing tool, hold down the (left or right) "Shift" key and start drawing!
You can also use this new functionality with a few other drawing functions:

























































































































This figure was created with four mouse clicks, using the "outline rectangle" drawing tool.
But it does not only work with tubes:






















































Selecting any acid pool or acid element and drawing with the outline rectangle tool again can create the above with three mouse clicks!
Another nice use are conveyor belts:
















































































































































Only three mouse clicks with the line drawing tool (and selecting a differently coloured conveyor belt element after each line).
































































One mouse click with any Supaplex style "chip" (wall) element.
















































One click with the "filled rectangles" tool.
I have also added a few not-so-obvious functions: If you click on a closed door (like exit, key gate, switch gate, time gate etc.) with "Shift" pressed, it changes to the open variant (and vice versa). The same happens with some other elements (emerald <-> wall with emerald, empty/filled Sokoban element, on/off lamp, just to name a few).
If there are more ideas that fit into this scheme, just let me know! :-)