Fix bug where vertically aligned text would creep downward

README.md

@@ -1,5 +1,7 @@
 # typeset
 
+[![Go Reference](https://pkg.go.dev/badge/git.tebibyte.media/tomo/typeset.svg)](https://pkg.go.dev/git.tebibyte.media/tomo/typeset)
+
 Typeset provides utilities for text layout, wrapping, and rendering.
 
 The state of a text layout is stored in a TypeSetter, and it can be drawn to any

layout.go

@@ -8,12 +8,11 @@ import "golang.org/x/image/math/fixed"
 type Align int
 
 const (
-	// AlignLeft aligns the start of each line to the beginning point
-	// of each dot.
-	AlignLeft Align = iota
-	AlignRight
-	AlignCenter
-	AlignJustify
+	//                              X     |     Y
+	AlignStart  Align = iota // left      | top
+	AlignMiddle              // center    | center
+	AlignEnd                 // right     | bottom
+	AlignEven                // justified | evenly spaced
 )
 
 // RuneLayout contains layout information for a single rune relative to its
@@ -150,11 +149,7 @@ func DoLine (text []rune, face font.Face, wrap bool, width fixed.Int26_6) (line
 
 	// set the width of the line's content.
 	line.ContentWidth = lastWord.X + lastWord.Width
-	if wrap {
-		line.Width = width
-	} else {
-		line.Width = line.ContentWidth
-	}
+	line.Width = width
 	line.SpaceAfter = lastWord.SpaceAfter
 	return
 }
@@ -174,17 +169,17 @@ func (line *LineLayout) Length () int {
 // method.
 func (line *LineLayout) Align (align Align) {
 	if len(line.Words) == 0 { return }
-
-	if align == AlignJustify {
+	
+	if align == AlignEven {
 		line.justify()
 		return
 	}
 
 	leftOffset := -line.Words[0].X
 
-	if align == AlignCenter {
+	if align == AlignMiddle {
 		leftOffset += (line.Width - line.ContentWidth) / 2
-	} else if align == AlignRight {
+	} else if align == AlignEnd {
 		leftOffset += line.Width - line.ContentWidth
 	}
 
@@ -195,7 +190,7 @@ func (line *LineLayout) Align (align Align) {
 
 func (line *LineLayout) justify () {
 	if len(line.Words) < 2 {
-		line.Align(AlignLeft)
+		line.Align(AlignStart)
 		return
 	}
 
@@ -206,8 +201,8 @@ func (line *LineLayout) justify () {
 		trueContentWidth += word.Width
 	}
 
-	spaceCount   := fixed.Int26_6(len(line.Words) - 1)
-	spacePerWord := (line.Width - trueContentWidth) / spaceCount
+	spaceCount   := len(line.Words) - 1
+	spacePerWord := (line.Width - trueContentWidth) / fixed.Int26_6(spaceCount)
 	x := fixed.Int26_6(0)
 	for index, word := range line.Words {
 		line.Words[index].X = x

setter.go

@@ -14,11 +14,10 @@ type TypeSetter struct {
 	layoutClean bool
 	alignClean  bool
 	
-	align Align
-	face  font.Face
-	maxWidth  int
-	maxHeight int
-	wrap      bool
+	hAlign, vAlign Align
+	face           font.Face
+	width, height  int
+	wrap           bool
 	
 	minWidth          fixed.Int26_6
 	layoutBounds      image.Rectangle
@@ -34,14 +33,15 @@ func (setter *TypeSetter) needLayout () {
 	setter.layoutBounds      = image.Rectangle { }
 	setter.layoutBoundsSpace = image.Rectangle { }
 	setter.minWidth          = 0
-	if setter.face  == nil { return }
+	if setter.face == nil { return }
 
 	horizontalExtent      := fixed.Int26_6(0)
 	horizontalExtentSpace := fixed.Int26_6(0)
 	metrics               := setter.face.Metrics()
 	remaining             := setter.text
 	y                     := fixed.Int26_6(0)
-	
+
+	// function to add line and update bounds statistics
 	addLine := func (line LineLayout) {
 		line.Y = y
 		y += metrics.Height
@@ -59,7 +59,7 @@ func (setter *TypeSetter) needLayout () {
 	for len(remaining) > 0 {
 		line, remainingFromLine := DoLine (
 			remaining, setter.face, setter.wrap,
-			fixed.I(setter.maxWidth))
+			fixed.I(setter.width))
 		remaining = remainingFromLine
 		addLine(line)
 	}
@@ -71,23 +71,22 @@ func (setter *TypeSetter) needLayout () {
 		setter.lines[len(setter.lines) - 1].BreakAfter
 	if needBlankLine { addLine(LineLayout { }) }
 
+	// if we are wrapping text, the width must be the user-set width
+	if setter.wrap {
+		horizontalExtent      = fixed.I(setter.width)
+		horizontalExtentSpace = fixed.I(setter.width) 
+	}
+
 	// calculate layout boundaries
 	setter.minWidth = horizontalExtentSpace
 	setter.layoutBounds.Max.X      = horizontalExtent.Round()
 	setter.layoutBoundsSpace.Max.X = horizontalExtentSpace.Round()
 
 	y -= metrics.Height
-	if setter.maxHeight == 0 {
-		setter.layoutBounds.Min.Y = -metrics.Ascent.Round()
-		setter.layoutBounds.Max.Y =
-			y.Round() +
-			metrics.Descent.Round()
-	} else {
-		setter.layoutBounds.Min.Y = -metrics.Ascent.Round()
-		setter.layoutBounds.Max.Y =
-			setter.maxHeight -
-			metrics.Ascent.Round()
-	}
+	setter.layoutBounds.Min.Y = -metrics.Ascent.Round()
+	setter.layoutBounds.Max.Y =
+		y.Round() +
+		metrics.Descent.Round()
 	setter.layoutBoundsSpace.Min.Y = setter.layoutBounds.Min.Y
 	setter.layoutBoundsSpace.Max.Y = setter.layoutBounds.Max.Y
 }
@@ -97,18 +96,76 @@ func (setter *TypeSetter) needAlignedLayout () {
 	setter.needLayout()
 	setter.alignClean = true
 
+	setter.alignHorizontally()
+	setter.alignVertically()
+}
+
+// should only be called from within setter.needAlignedLayout
+func (setter *TypeSetter) alignHorizontally () {
+	if len(setter.lines) == 0 { return }
+	
 	for index := range setter.lines {
-		align := setter.align
-		if align == AlignJustify {
+		align := setter.hAlign
+
+		// if the horizontal align is even, align lines with breaks
+		// after them to the left anyways
+		if align == AlignEven {
 			except :=
 				index == len(setter.lines) - 1 ||
 				setter.lines[index].BreakAfter
-			if except { align = AlignLeft }
+			if except { align = AlignStart }
 		}
+
+		// align line
 		setter.lines[index].Align(align)
 	}
 }
 
+// should only be called from within setter.needAlignedLayout
+func (setter *TypeSetter) alignVertically () {
+	if setter.height     == 0 { return }
+	if len(setter.lines) == 0 { return }
+	if setter.vAlign == AlignEven {
+		setter.justifyVertically()
+		return
+	}
+
+	// determine how much to shift lines
+	topOffset     := fixed.I(0)
+	contentHeight := setter.layoutBoundsSpace.Dy()
+	if setter.vAlign == AlignMiddle {
+		topOffset += fixed.I((setter.height - contentHeight) / 2)
+	} else if setter.vAlign == AlignEnd {
+		topOffset += fixed.I(setter.height - contentHeight)
+	}
+
+	// we may be re-aligning already aligned text. if the text is shifted
+	// away from the origin, account for that.
+	if len(setter.lines) > 0 {
+		topOffset -= setter.lines[0].Y
+	}
+
+	// shift lines
+	for index := range setter.lines {
+		setter.lines[index].Y += topOffset
+	}
+}
+
+// should only be called from within setter.alignVertically
+func (setter *TypeSetter) justifyVertically () {
+	spaceCount    := len(setter.lines) - 1
+	contentHeight := setter.layoutBoundsSpace.Dy()
+	spacePerLine  :=
+		fixed.Int26_6(setter.height - contentHeight) /
+		fixed.Int26_6(spaceCount)
+	
+	y := fixed.Int26_6(0)
+	for index := range setter.lines {
+		setter.lines[index].Y = y
+		y += spacePerLine + setter.LineHeight()
+	}
+}
+
 // SetWrap sets whether or not the text wraps around and forms new lines.
 func (setter *TypeSetter) SetWrap (wrap bool) {
 	if setter.wrap == wrap { return }
@@ -118,9 +175,10 @@ func (setter *TypeSetter) SetWrap (wrap bool) {
 
 // SetAlign sets the alignment method of the typesetter.
 func (setter *TypeSetter) SetAlign (horizontal, vertical Align) {
-	if setter.align == horizontal { return }
+	if setter.hAlign == horizontal && setter.vAlign == vertical { return }
 	setter.alignClean = false
-	setter.align = horizontal
+	setter.hAlign = horizontal
+	setter.vAlign = vertical
 }
 
 // SetText sets the text content of the typesetter.
@@ -141,20 +199,20 @@ func (setter *TypeSetter) SetFace (face font.Face) {
 // SetWidth sets the width of the typesetter. Text will still be able
 // to overflow outside of this width if wrapping is disabled.
 func (setter *TypeSetter) SetWidth (width int) {
-	if setter.maxWidth == width { return }
+	if setter.width == width { return }
 	setter.layoutClean = false
 	setter.alignClean  = false
-	setter.maxWidth = width
+	setter.width = width
 }
 
 // SetHeight sets the height of the typesetter. If the height is greater than
 // zero, no lines will be laid out past it. If the height is zero, the text's
 // maximum height will not be constrained.
 func (setter *TypeSetter) SetHeight (heignt int) {
-	if setter.maxHeight == heignt { return }
+	if setter.height == heignt { return }
 	setter.layoutClean = false
 	setter.alignClean  = false
-	setter.maxHeight = heignt
+	setter.height = heignt
 }
 
 // Em returns the width of one emspace according to the typesetter's font, which
@@ -173,12 +231,12 @@ func (setter *TypeSetter) LineHeight () fixed.Int26_6 {
 
 // Width returns the height of the typesetter as set by SetWidth.
 func (setter *TypeSetter) Width () int {
-	return setter.maxWidth
+	return setter.width
 }
 
 // Height returns the height of the typesetter as set by SetHeight.
 func (setter *TypeSetter) Height () int {
-	return setter.maxHeight
+	return setter.height
 }
 
 // Face returns the TypeSetter's font face as set by SetFace.