Source File
	aat_layout_kerx.go

Belonging Package
	github.com/go-text/typesetting/harfbuzz

package harfbuzz

import (
	"fmt"

	"github.com/go-text/typesetting/font"
	"github.com/go-text/typesetting/font/opentype/tables"
)

func (c *aatApplyContext) applyKernx(kerx font.Kernx, accelerators []kernxSubtableAccelerator) {
	var ret, seenCrossStream bool

	c.buffer.unsafeToConcat(0, maxInt)

	c.setupBufferGlyphSet()

	for i, st := range kerx {
		var reverse bool

		if !st.IsExtended && st.IsVariation() {
			continue
		}

		if c.buffer.Props.Direction.isHorizontal() != st.IsHorizontal() {
			continue
		}

		c.firstSet = accelerators[i].first_set
		c.secondSet = accelerators[i].second_set
		c.machineClassCache = accelerators[i].class_cache

		if !c.bufferIntersectsMachine() {
			if debugMode {
				fmt.Printf("AAT kerx : skipped subtable %d because no glyph matches\n", i)
			}
			continue
		}

		reverse = st.IsBackwards() != c.buffer.Props.Direction.isBackward()

		if debugMode {
			fmt.Printf("AAT kerx : start subtable %d\n", i)
		}

		if !seenCrossStream && st.IsCrossStream() {
			/* Attach all glyphs into a chain. */
			seenCrossStream = true
			pos := c.buffer.Pos
			for i := range pos {
				pos[i].attachType = attachTypeCursive
				if c.buffer.Props.Direction.isForward() {
					pos[i].attachChain = -1
				} else {
					pos[i].attachChain = +1
				}
				/* We intentionally don't set HB_BUFFER_SCRATCH_FLAG_HAS_GPOS_ATTACHMENT,
				 * since there needs to be a non-zero attachment for post-positioning to
				 * be needed. */
			}
		}

		if reverse != c.bufferIsReversed {
			c.reverseBuffer()
		}

		applied := c.applyKerxSubtable(st)
		ret = ret || applied

		if debugMode {
			fmt.Printf("AAT kerx : end subtable %d\n", i)
			fmt.Println(c.buffer.Pos)
		}
	}

	if c.bufferIsReversed {
		c.reverseBuffer()
	}
}

func (c *aatApplyContext) applyKerxSubtable(st font.KernSubtable) bool {
	if debugMode {
		fmt.Printf("\tKERNX table %T\n", st.Data)
	}
	switch data := st.Data.(type) {
	case font.Kern0:
		if !c.plan.requestedKerning {
			return false
		}
		if st.IsBackwards() {
			return false
		}
		kern(kern0Accelerator{data, c}, st.IsCrossStream(), c.font, c.buffer, c.plan.kernMask, true)
	case font.Kern1:
		crossStream := st.IsCrossStream()
		if !c.plan.requestedKerning && !crossStream {
			return false
		}
		dc := driverContextKerx1{c: c, table: data, crossStream: crossStream}
		driver := newStateTableDriver(data.Machine, c.face)
		driver.drive(&dc, c)
	case font.Kern2:
		if !c.plan.requestedKerning {
			return false
		}
		if st.IsBackwards() {
			return false
		}
		kern(kern2Accelerator{data, c}, st.IsCrossStream(), c.font, c.buffer, c.plan.kernMask, true)
	case font.Kern3:
		if !c.plan.requestedKerning {
			return false
		}
		if st.IsBackwards() {
			return false
		}
		kern(data, st.IsCrossStream(), c.font, c.buffer, c.plan.kernMask, true)
	case font.Kern4:
		crossStream := st.IsCrossStream()
		if !c.plan.requestedKerning && !crossStream {
			return false
		}
		dc := driverContextKerx4{c: c, table: data, actionType: data.ActionType()}
		driver := newStateTableDriver(data.Machine, c.face)
		driver.drive(&dc, c)
	case font.Kern6:
		if !c.plan.requestedKerning {
			return false
		}
		if st.IsBackwards() {
			return false
		}
		kern(kern6Accelerator{data, c}, st.IsCrossStream(), c.font, c.buffer, c.plan.kernMask, true)
	}
	return true
}

// add a cache layout
type kern0Accelerator struct {
	table   font.Kern0
	context *aatApplyContext
}

func (k0 kern0Accelerator) KernPair(left, right GID) int16 {
	if !k0.context.firstSet.hasGlyph(left) || !k0.context.secondSet.hasGlyph(right) {
		return 0
	}
	return k0.table.KernPair(left, right)
}

// Kernx1 state entry flags
const (
	kerx1Push        = 0x8000 // If set, push this glyph on the kerning stack.
	kerx1DontAdvance = 0x4000 // If set, don't advance to the next glyph before going to the new state.
	kerx1Reset       = 0x2000 // If set, reset the kerning data (clear the stack)
	kern1Offset      = 0x3FFF // Byte offset from beginning of subtable to the  value table for the glyphs on the kerning stack.
)

type driverContextKerx1 struct {
	c           *aatApplyContext
	table       font.Kern1
	stack       [8]int
	depth       int
	crossStream bool
}

func (driverContextKerx1) inPlace() bool { return true }

func (dc driverContextKerx1) isActionable(entry tables.AATStateEntry) bool {
	return entry.AsKernxIndex() != 0xFFFF
}

func (dc *driverContextKerx1) transition(buffer *Buffer, driver stateTableDriver, entry tables.AATStateEntry) {
	flags := entry.Flags

	if flags&kerx1Reset != 0 {
		dc.depth = 0
	}

	if flags&kerx1Push != 0 {
		if dc.depth < len(dc.stack) {
			dc.stack[dc.depth] = buffer.idx
			dc.depth++
		} else {
			dc.depth = 0 /* Probably not what CoreText does, but better? */
		}
	}

	if dc.isActionable(entry) && dc.depth != 0 {
		tupleCount := 1 // we do not support tupleCount > 0

		kernIdx := entry.AsKernxIndex()

		actions := dc.table.Values[kernIdx:]
		if len(actions) < tupleCount*dc.depth {
			dc.depth = 0
			return
		}

		kernMask := dc.c.plan.kernMask

		/* From Apple 'kern' spec:
		 * "Each pops one glyph from the kerning stack and applies the kerning value to it.
		 * The end of the list is marked by an odd value... */
		var last bool
		for !last && dc.depth != 0 {
			dc.depth--
			idx := dc.stack[dc.depth]
			v := actions[0]
			actions = actions[tupleCount:]
			if idx >= len(buffer.Pos) {
				continue
			}

			/* "The end of the list is marked by an odd value..." */
			last = v&1 != 0
			v &= ^1

			o := &buffer.Pos[idx]
			if buffer.Props.Direction.isHorizontal() {
				if dc.crossStream {
					/* The following flag is undocumented in the spec, but described
					 * in the 'kern' table example. */
					if v == -0x8000 {
						o.attachType = attachTypeNone
						o.attachChain = 0
						o.YOffset = 0
					} else if o.attachType != 0 {
						o.YOffset += dc.c.font.emScaleY(v)
						buffer.scratchFlags |= bsfHasGPOSAttachment
					}
				} else if buffer.Info[idx].Mask&kernMask != 0 {
					scaled := dc.c.font.emScaleX(v)
					o.XAdvance += scaled
					o.XOffset += scaled
				}
			} else {
				if dc.crossStream {
					/* CoreText doesn't do crossStream kerning in vertical.  We do. */
					if v == -0x8000 {
						o.attachType = attachTypeNone
						o.attachChain = 0
						o.XOffset = 0
					} else if o.attachType != 0 {
						o.XOffset += dc.c.font.emScaleX(v)
						buffer.scratchFlags |= bsfHasGPOSAttachment
					}
				} else if buffer.Info[idx].Mask&kernMask != 0 {
					o.YAdvance += dc.c.font.emScaleY(v)
					o.YOffset += dc.c.font.emScaleY(v)
				}
			}
		}
	}
}

type kern2Accelerator struct {
	table   font.Kern2
	context *aatApplyContext
}

func (k2 kern2Accelerator) KernPair(left, right GID) int16 {
	if !k2.context.firstSet.hasGlyph(left) || !k2.context.secondSet.hasGlyph(right) {
		return 0
	}
	return k2.table.KernPair(left, right)
}

type driverContextKerx4 struct {
	c          *aatApplyContext
	table      font.Kern4
	mark       int
	markSet    bool
	actionType uint8
}

func (driverContextKerx4) inPlace() bool { return true }

func (driverContextKerx4) isActionable(entry tables.AATStateEntry) bool {
	return entry.AsKernxIndex() != 0xFFFF
}

func (dc *driverContextKerx4) transition(buffer *Buffer, driver stateTableDriver, entry tables.AATStateEntry) {
	ankrActionIndex := entry.AsKernxIndex()
	if dc.markSet && ankrActionIndex != 0xFFFF && buffer.idx < len(buffer.Pos) {
		o := buffer.curPos(0)
		switch dc.actionType {
		case 0: /* Control Point Actions.*/
			/* Indexed into glyph outline. */
			action := dc.table.Anchors.(tables.KerxAnchorControls).Anchors[ankrActionIndex]

			markX, markY, okMark := dc.c.font.getGlyphContourPointForOrigin(dc.c.buffer.Info[dc.mark].Glyph,
				action.Mark, LeftToRight)
			currX, currY, okCurr := dc.c.font.getGlyphContourPointForOrigin(dc.c.buffer.cur(0).Glyph,
				action.Current, LeftToRight)
			if !okMark || !okCurr {
				return
			}

			o.XOffset = markX - currX
			o.YOffset = markY - currY

		case 1: /* Anchor Point Actions. */
			/* Indexed into 'ankr' table. */
			action := dc.table.Anchors.(tables.KerxAnchorAnchors).Anchors[ankrActionIndex]

			markAnchor := dc.c.ankrTable.GetAnchor(gID(dc.c.buffer.Info[dc.mark].Glyph), int(action.Mark))
			currAnchor := dc.c.ankrTable.GetAnchor(gID(dc.c.buffer.cur(0).Glyph), int(action.Current))

			o.XOffset = dc.c.font.emScaleX(markAnchor.X) - dc.c.font.emScaleX(currAnchor.X)
			o.YOffset = dc.c.font.emScaleY(markAnchor.Y) - dc.c.font.emScaleY(currAnchor.Y)

		case 2: /* Control Point Coordinate Actions. */
			action := dc.table.Anchors.(tables.KerxAnchorCoordinates).Anchors[ankrActionIndex]
			o.XOffset = dc.c.font.emScaleX(action.MarkX) - dc.c.font.emScaleX(action.CurrentX)
			o.YOffset = dc.c.font.emScaleY(action.MarkY) - dc.c.font.emScaleY(action.CurrentY)
		}
		o.attachType = attachTypeMark
		o.attachChain = int16(dc.mark - buffer.idx)
		if dc.c.bufferIsReversed {
			o.attachChain = -o.attachChain
		}
		buffer.scratchFlags |= bsfHasGPOSAttachment
	}

	const Mark = 0x8000 /* If set, remember this glyph as the marked glyph. */
	if entry.Flags&Mark != 0 {
		dc.markSet = true
		dc.mark = buffer.idx
	}
}

type kern6Accelerator struct {
	table   font.Kern6
	context *aatApplyContext
}

func (k6 kern6Accelerator) KernPair(left, right GID) int16 {
	if !k6.context.firstSet.hasGlyph(left) || !k6.context.secondSet.hasGlyph(right) {
		return 0
	}
	return k6.table.KernPair(left, right)
}

type kernxSubtableAccelerator struct {
	first_set   intSet
	second_set  intSet
	class_cache aatClassCache
}

func newKernxSubtableAccelerator(subtable font.KernSubtable) kernxSubtableAccelerator {
	var out kernxSubtableAccelerator
	out.class_cache.clear()
	switch st := subtable.Data.(type) {
	case font.Kern0:
		for _, pair := range st {
			out.first_set.add(uint32(pair.Left))
			out.second_set.add(uint32(pair.Right))
		}
	case font.Kern1:
		collectLookupGlyphs(&out.first_set, st.Machine.Class)
		// collectLookupGlyphs (second_set, num_glyphs); // second_set is unused for machine kerning
	case font.Kern2:
		collectLookupGlyphs(&out.first_set, st.Left)
		collectLookupGlyphs(&out.second_set, st.Right)
	case font.Kern3:
		if L := len(st.LeftClass); L != 0 {
			out.first_set.addRange(0, uint32(L-1))
			out.second_set.addRange(0, uint32(L-1))
		}
	case font.Kern4:
		collectLookupGlyphs(&out.first_set, st.Machine.Class)
		// collectLookupGlyphs (second_set, num_glyphs); // second_set is unused for machine kerning
	case font.Kern6:
		collectLookupGlyphs(&out.first_set, st.Row)
		collectLookupGlyphs(&out.second_set, st.Column)
	}
	return out
}

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