typeset/setter.go

package typeset

import "image"
import "golang.org/x/image/font"
import "golang.org/x/image/math/fixed"

// TypeSetter manages several lines of text, and can perform layout operations
// on them. It automatically avoids performing redundant work. It has no
// constructor and its zero value can be used safely.
type TypeSetter struct {
	lines []LineLayout
	text []rune
	
	layoutClean bool
	alignClean  bool
	
	hAlign, vAlign Align
	face           font.Face
	width, height  int
	wrap           bool
	
	minWidth          fixed.Int26_6
	layoutBounds      image.Rectangle
	layoutBoundsSpace image.Rectangle
}

func (setter *TypeSetter) needLayout () {
	if setter.layoutClean { return }
	setter.layoutClean = true
	setter.alignClean  = false

	setter.lines = nil
	setter.layoutBounds      = image.Rectangle { }
	setter.layoutBoundsSpace = image.Rectangle { }
	setter.minWidth          = 0
	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
		if line.ContentWidth > horizontalExtent {
			horizontalExtent = line.ContentWidth
		}
		lineWidthSpace := line.ContentWidth + line.SpaceAfter
		if lineWidthSpace > horizontalExtentSpace {
			horizontalExtentSpace = lineWidthSpace
		}
		setter.lines = append(setter.lines, line)
	}

	// process every line until there are no more remaining runes
	for len(remaining) > 0 {
		line, remainingFromLine := DoLine (
			remaining, setter.face, setter.wrap,
			fixed.I(setter.width))
		remaining = remainingFromLine
		addLine(line)
	}

	// if there were no lines processed or the last line has a break after
	// it, add a blank line at the end
	needBlankLine :=
		len(setter.lines) == 0 ||
		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
	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
}

func (setter *TypeSetter) needAlignedLayout () {
	if setter.alignClean && setter.layoutClean { return }
	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.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 = 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 }
	setter.layoutClean = false
	setter.wrap = wrap
}

// SetAlign sets the alignment method of the typesetter.
func (setter *TypeSetter) SetAlign (horizontal, vertical Align) {
	if setter.hAlign == horizontal && setter.vAlign == vertical { return }
	setter.alignClean = false
	setter.hAlign = horizontal
	setter.vAlign = vertical
}

// SetText sets the text content of the typesetter.
func (setter *TypeSetter) SetText (text []rune) {
	setter.layoutClean = false
	setter.alignClean  = false
	setter.text = text
}

// SetFace sets the font face of the typesetter.
func (setter *TypeSetter) SetFace (face font.Face) {
	if setter.face == face { return }
	setter.layoutClean = false
	setter.alignClean  = false
	setter.face = 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.width == width { return }
	setter.layoutClean = false
	setter.alignClean  = false
	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.height == heignt { return }
	setter.layoutClean = false
	setter.alignClean  = false
	setter.height = heignt
}

// Em returns the width of one emspace according to the typesetter's font, which
// is the width of the capital letter 'M'.
func (setter *TypeSetter) Em () (width fixed.Int26_6) {
	if setter.face == nil { return 0 }
	width, _ = setter.face.GlyphAdvance('M')
	return
}

// LineHeight returns the height of one line according to the typesetter's font.
func (setter *TypeSetter) LineHeight () fixed.Int26_6 {
	if setter.face == nil { return 0 }
	return setter.face.Metrics().Height
}

// Width returns the height of the typesetter as set by SetWidth.
func (setter *TypeSetter) Width () int {
	return setter.width
}

// Height returns the height of the typesetter as set by SetHeight.
func (setter *TypeSetter) Height () int {
	return setter.height
}

// Face returns the TypeSetter's font face as set by SetFace.
func (setter *TypeSetter) Face () font.Face {
	return setter.face
}

// Length returns the amount of runes in the typesetter.
func (setter *TypeSetter) Length () int {
	return len(setter.text)
}

// RuneIterator is a function that can iterate accross a typesetter's runes.
type RuneIterator func (
	index    int,
	char     rune,
	position fixed.Point26_6,
) (
	keepGoing bool,
)

// For calls the specified iterator for every rune in the typesetter. If the
// iterator returns false, the loop will immediately stop.
func (setter *TypeSetter) For (iterator RuneIterator) {
	setter.needAlignedLayout()

	index := 0
	lastLineY := fixed.Int26_6(0)
	lastCharRightBound := fixed.Int26_6(0)
	for _, line := range setter.lines {
		lastLineY = line.Y
		for _, word := range line.Words {
		for _, char := range word.Runes {
			lastCharRightBound = word.X + char.X + char.Width
			keepGoing := iterator (index, char.Rune, fixed.Point26_6 {
				X: word.X + char.X,
				Y: line.Y,
			})
			if !keepGoing { return }
			index ++
		}}
		
		if line.BreakAfter {
			keepGoing := iterator (index, '\n', fixed.Point26_6 {
				X: lastCharRightBound,
				Y: line.Y,
			})
			if !keepGoing { return }
			index ++
		}
	}
	
	keepGoing := iterator (index, '\000', fixed.Point26_6 {
		X: lastCharRightBound,
		Y: lastLineY,
	})
	if !keepGoing { return }
	index ++
}

// AtPosition returns the index of the rune at the specified position.
func (setter *TypeSetter) AtPosition (position fixed.Point26_6) (index int) {
	setter.needAlignedLayout()
	
	if setter.lines == nil { return }
	if setter.face  == nil { return }

	// find the first line who's bottom bound is greater than position.Y. if
	// we haven't found it, then dont set the line variable (defaults to the
	// last line)
	metrics  := setter.face.Metrics()
	lastLine := setter.lines[len(setter.lines) - 1]
	for _, curLine := range setter.lines {	
		if curLine.Y + metrics.Descent > position.Y {
			lastLine = curLine
			break
		}
		
		index += curLine.Length()
	}

	if lastLine.Words == nil { return }

	// find the first rune who's right bound is greater than position.X.
	for _, curWord := range lastLine.Words {
		for _, curChar := range curWord.Runes {
			x := curWord.X + curChar.X + curChar.Width
			if x > position.X { goto foundRune }
			index ++
		}
	}
	foundRune:
	return
}

// PositionAt returns the position of the rune at the specified index.
func (setter *TypeSetter) PositionAt (index int) (position fixed.Point26_6) {
	setter.needAlignedLayout()
	
	setter.For (func (i int, r rune, p fixed.Point26_6) bool {
		position = p
		return i < index
	})
	return
}

// LayoutBounds returns the semantic bounding box of the text. The origin point
// (0, 0) of the rectangle corresponds to the origin of the first line's
// baseline.
func (setter *TypeSetter) LayoutBounds () (image.Rectangle) {
	setter.needLayout()
	return setter.layoutBounds
	
}

// LayoutBoundsSpace is like LayoutBounds, but it also takes into account the
// trailing whitespace at the end of each line (if it exists).
func (setter *TypeSetter) LayoutBoundsSpace () (image.Rectangle) {
	setter.needLayout()
	return setter.layoutBoundsSpace
}

// MinimumSize returns the minimum width and height needed to display text. If
// wrapping is enabled, this method will return (Em(), 0) 
func (setter *TypeSetter) MinimumSize () image.Point {
	setter.needLayout()
	if setter.wrap {
		return image.Pt(setter.Em().Round(), 0)
	}

	width  := setter.minWidth
	height := fixed.Int26_6(len(setter.lines)) * setter.LineHeight()

	return image.Pt(width.Round(), height.Round())
}

// ReccomendedHeightFor returns the reccomended max height if the text were to
// have its maximum width set to the given width. This does not alter the
// typesetter's state.
func (setter *TypeSetter) ReccomendedHeightFor (width int) (height int) {
	setter.needLayout()
	
	if setter.lines == nil { return }
	if setter.face  == nil { return }

	metrics := setter.face.Metrics()
	dot := fixed.Point26_6 { X: 0, Y: metrics.Height }
	firstWord := true
	for _, line := range setter.lines {
		for _, word := range line.Words {
			if word.Width + dot.X > fixed.I(width) && !firstWord {
				dot.Y += metrics.Height
				dot.X = 0
				firstWord = true
			}
			dot.X += word.Width + word.SpaceAfter
			firstWord = false
		}
		if line.BreakAfter {
			dot.Y += metrics.Height
			dot.X = 0
			firstWord = true
		}
	}

	return dot.Y.Round()
}