text: allow disabling space trimming

This commit adds a shaping parameter that disables the trimming of trailing
whitespace from lines. Text editors and similar use-cases want trailing whitspace
glyphs to be selectable, which means they must occupy space.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

text/gotext.go

@@ -490,10 +490,11 @@ func wrapPolicyToGoText(p WrapPolicy) shaping.LineBreakPolicy {
 // shapeAndWrapText invokes the text shaper and returns wrapped lines in the shaper's native format.
 func (s *shaperImpl) shapeAndWrapText(params Parameters, txt []rune) (_ []shaping.Line, truncated int) {
 	wc := shaping.WrapConfig{
-		Direction:          mapDirection(params.Locale.Direction),
-		TruncateAfterLines: params.MaxLines,
-		TextContinues:      params.forceTruncate,
-		BreakPolicy:        wrapPolicyToGoText(params.WrapPolicy),
+		Direction:                     mapDirection(params.Locale.Direction),
+		TruncateAfterLines:            params.MaxLines,
+		TextContinues:                 params.forceTruncate,
+		BreakPolicy:                   wrapPolicyToGoText(params.WrapPolicy),
+		DisableTrailingWhitespaceTrim: params.DisableSpaceTrim,
 	}
 	families := s.defaultFaces
 	if params.Font.Typeface != "" {

text/shaper.go

@@ -76,6 +76,11 @@ type Parameters struct {
 	// text with a MaxLines. It is unexported because this behavior only makes sense for the
 	// shaper to control when it iterates paragraphs of text.
 	forceTruncate bool
+
+	// DisableSpaceTrim prevents the width of the final whitespace glyph on a line from being zeroed.
+	// This is desirable for text editors (so that the whitespace can be selected), but is undesirable
+	// for ordinary display text.
+	DisableSpaceTrim bool
 }
 
 type FontFace = giofont.FontFace