from preamble:

"Change Set:		ColorSeesTurtleTrailsToo-nk
Date:			4 July 2003
Author:			Ned Konz

v2: made the turtle trails form deeper if necessary. Maybe clear the
turtle trails when the preference changes.

This adds a per-Project Preference called #colorSeesTurtleTrailsToo.

When this preference is set, the #color:sees: and #touchesColor: (but
not the #colorUnder) methods will take into account the turtle trails in
a Morphs' playfield. This was not previously happening for Morphs in the
World.

This makes it possible to write eToys scripts that can see the turtle
trails.

By default, this preference is true, for backwards compatibility. So
embedded playfields (scripting areas, etc.) will still work the same,
and the World will gain the ability to see the turtle trails.

This also avoids an unnecessary ColorPatchCanvas copy that was in
#patchAt:without:andNothingAbove:

It also localizes the patch extent to the Morph's own pasteUpMorph
rather than looking at the World, for efficiency and to prevent
surprises when other playfields may be overhead.

"

Preferences preferenceAt: #colorSeesTurtleTrailsToo
ifAbsent: [ Preferences
	addPreference: #colorSeesTurtleTrailsToo
	categories: #(scripting)
	default: true
	balloonHelp: 'if true, the ''color:sees:'' and ''touchesColor:'' tests
in eToys (but not ''colorUnder'') will also see turtle trails'
	projectLocal: true
	changeInformee: #Project
	changeSelector: #clearAllTurtleTrailsIfWrongDepth
].!
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