warn when painting will have no effect, explaining reason
Submitted by david gowers
Link to original bug (#421434)
Description
Several times, after using the drawing tool opacity adjustment (via keyboard shortcuts), I have set the opacity to 0% accidentally, and then became completely baffled because drawing had absolutely no effect, and occasionally went to file a bug before realizing the source of the problem.
I think that either: a. Opacity should be limited to 1.0...100.0% (or possibly (1/2.55)%..100.0%) or b. A message should be shown in the status bar when attempting to paint with opacity == 0% -- perhaps drawing should be disabled, also.
I believe (a) or something similar is the better solution, though (b) will be less troublesome.
Most often, this has caused me problems by:
- I finish a GIMP session, accidentally setting opacity -> 0% just before finishing
- The opacity setting is saved
- It is reused next time I start gimp, so I start out with 0% opacity.
So it might also be useful to force opacity settings to be >= (1/2.55).