A background mask punches the drawing out behind a piece of text so it stays readable over hatching or dense linework. AutoCAD offers it — through three different places depending on the object type, one object at a time. BACKDROP does all three types, across a whole selection, from one dialog.
What BackDrop does
Select any mixture of MText, multileaders and dimensions, set the options once, and every object takes them.
Use Background Mask turns it on or off. Mask Offset sets how far the mask extends past the text, as a multiple of text height, between 1 and 5 — and the >> button lets you pick it in the drawing instead of typing a number. Transparent hides what is behind the text without painting a colour. Fill Color sets the mask colour when it is not transparent.
Settings persist between AutoCAD sessions.
Transparent is normally what you want. A coloured mask that matches the screen background looks right on screen and still plots as a solid block — which is the classic way a masked note turns into a white rectangle on the issued drawing.
How to use it
- Load the routine with
APPLOAD, or put it on your support file search path. - Type
BACKDROP. - Select any mixture of MText, multileaders and dimensions.
- Set the options in the dialog. Use the
>>button beside the offset to pick a value in the drawing rather than typing it. - Click OK. Every object in the selection takes the settings.
How it works
Dimensions work differently from the other two, and that is most of the code. MText and multileaders carry their mask settings directly on the object. A dimension does not — its mask belongs to its dimension style. Masking one dimension without disturbing every other dimension that shares the style therefore means writing a style override onto that individual dimension, which is what the extended-data handling in the routine does.
Overrides are only written where one is actually needed. If a dimension’s own style already specifies the requested mask, the override is removed rather than added. That keeps the drawing clean: a set full of redundant style overrides is a set nobody can predict the behaviour of, and they accumulate silently.
Mask offset does not apply to dimensions. AutoCAD provides no mask offset for them, so the setting is simply ignored for any dimension in the selection. Mixed selections are fine — the MText and multileaders take the offset, the dimensions take everything else.
Notes and limits
- Use transparent unless you specifically want a colour. A mask coloured to match the screen background will plot solid.
- Offset is ignored on dimensions because AutoCAD has no such setting for them, not because the routine skips it.
- Dimension masks are style overrides. Anything that clears overrides — reapplying the style, for instance — clears the mask with them.
- Masks affect plot order. A mask hides what is behind it, so check the draw order if something has disappeared that should not have.
Download and details
| Name | BackDrop — control background masks across a whole selection |
| Download | BackDrop.lsp — 28.5 KB, plain AutoLISP source. Downloads directly; no zip to unpack. |
| Type | AutoCAD AutoLISP routine |
| Command | BACKDROP |
| Requires | the ActiveX layer (loaded automatically by the routine with vl-load-com); nothing extra — the dialog is written to a temporary file at run time and deleted again, so there is no .dcl to install. |
| Source size | 28.5 KB, 670 lines |
| Error handling | Yes — a *error* handler restores every system variable it changed, on cancel as well as on error. |
| Undo | The whole operation is wrapped in a single undo group, so one U reverses all of it. |
| Compatibility | AutoCAD (any release with AutoLISP), BricsCAD, ZWCAD, GstarCAD, ProgeCAD and other IntelliCAD-based platforms. AutoCAD LT needs a LISP enabler. No .NET, no ObjectARX, no installer. |
| Author | YZ, August 2026 |
| Licence | Free to use, supplied “as is” with no warranty. |
References
- TEXTFRAME LISP — draw a frame around text rather than masking behind it
- Pen sizes and line types — the linework a mask is protecting text from
- More free AutoLISP routines on this site
- Wisey’s Steel Shapes — free structural steel section drawing program