LayoutBounds can have a negative start

This causes the LayoutBounds of center-aligned, left-aligned text
to be more accurate

flow.go

@@ -18,11 +18,14 @@ func reflow (
 	metrics := face.Metrics()
 	
 	var dot fixed.Point26_6
+	const notSeen = -1
+	firstWord := notSeen
 	lineStart := 0
 	lineEnd   := 0
 	lastWord  := 0
 	lastToken := 0
 	nLines    := 0
+	firstLine := true
 
 	newline := func () {
 		// if the line isn't empty
@@ -31,13 +34,31 @@ func reflow (
 			alignLine (
 				tokens[lineStart:lineEnd],
 				size.X, xAlign, lineEnd == len(tokens))
-			
+
 			// calculate extents
-			lineMax, lineMaxSpace := calculateLineExtents (
-				tokens[lastWord],
-				tokens[lastToken])
-			if lineMax      > extents.Max.X      { extents.Max.X      = lineMax      }
-			if lineMaxSpace > extentsSpace.Max.X { extentsSpace.Max.X = lineMaxSpace }
+			var lineMin, lineMinSpace, lineMax, lineMaxSpace fixed.Int26_6
+
+			lineMinSpace = tokens[lineStart].position.X
+			if firstWord == notSeen {
+				lineMin = lineMinSpace
+			} else {
+				lineMin = tokens[firstWord].position.X
+			}
+			
+			lastWordTok   := tokens[lastWord]
+			lastTokenTok  := tokens[lastToken]
+			if lastWordTok.kind == tokenKindWord {
+				// the line had a word in it
+				lineMax = lastWordTok.position.X + lastWordTok.width
+			}
+			lineMaxSpace = lastTokenTok.position.X + lastTokenTok.width
+			// println(lineMax.String(), lineMaxSpace.String())
+				
+			if lineMin      < extents.Min.X      || firstLine { extents.Min.X      = lineMin      }
+			if lineMinSpace < extentsSpace.Min.X || firstLine { extentsSpace.Min.X = lineMinSpace }
+			if lineMax      > extents.Max.X                   { extents.Max.X      = lineMax      }
+			if lineMaxSpace > extentsSpace.Max.X              { extentsSpace.Max.X = lineMaxSpace }
+			firstLine = false
 		}
 
 		// update dot
@@ -47,6 +68,7 @@ func reflow (
 		// update indices, counts
 		lineStart = lineEnd
 		lastWord  = lineEnd
+		firstWord = notSeen
 		nLines ++
 	}
 
@@ -59,6 +81,9 @@ func reflow (
 			lastToken = index
 			if token.kind == tokenKindWord {
 				lastWord = index
+				if firstWord == notSeen {
+					firstWord = index
+				}
 			}
 		}
 
@@ -111,14 +136,12 @@ func fixedRectDy (rect fixed.Rectangle26_6) fixed.Int26_6 {
 	return rect.Max.Y - rect.Min.Y
 }
 
-func calculateLineExtents (lastWord, lastToken token) (lineMax, lineMaxSpace fixed.Int26_6) {
-	if lastWord.kind == tokenKindWord {
-		// the line had a word in it
-		lineMax = lastWord.position.X  + lastWord.width
-	}
-	lineMaxSpace = lastToken.position.X + lastToken.width
-	// println(lineMax.String(), lineMaxSpace.String())
-	return lineMax, lineMaxSpace
+func calculateLineExtents (
+	firstWord, firstToken, lastWord, lastToken token,
+) (
+	lineMin, lineMinSpace, lineMax, lineMaxSpace fixed.Int26_6,
+) {
+	return
 }
 
 func alignLinesVertically (tokens []token, height, contentHeight fixed.Int26_6, align Align) {