From ab80f5823df1d3bb062320cc89eccd8af642cf5f Mon Sep 17 00:00:00 2001
From: Nigel Tao <nigeltao@golang.org>
Date: Fri, 25 Oct 2013 20:07:33 +1100
Subject: [PATCH] freetype/truetype: implement SHP and DELTAP opcodes.

R=bsiegert
CC=golang-dev, remyoudompheng
https://codereview.appspot.com/16500043
---
 freetype/truetype/hint.go          | 58 ++++++++++++++++++++++++++++++
 freetype/truetype/opcodes.go       | 16 ++++-----
 freetype/truetype/truetype_test.go |  2 +-
 3 files changed, 67 insertions(+), 9 deletions(-)

diff --git a/freetype/truetype/hint.go b/freetype/truetype/hint.go
index 1312f54..1817958 100644
--- a/freetype/truetype/hint.go
+++ b/freetype/truetype/hint.go
@@ -480,6 +480,24 @@ func (h *Hinter) run(program []byte, pCurrent, pUnhinted, pInFontUnits []Point,
 				prevEnd = end
 			}
 
+		case opSHP0, opSHP1:
+			if top < int(h.gs.loop) {
+				return errors.New("truetype: hinting: stack underflow")
+			}
+			_, _, d, ok := h.displacement(opcode&1 == 0)
+			if !ok {
+				return errors.New("truetype: hinting: point out of range")
+			}
+			for ; h.gs.loop != 0; h.gs.loop-- {
+				top--
+				p := h.point(2, current, h.stack[top])
+				if p == nil {
+					return errors.New("truetype: hinting: point out of range")
+				}
+				h.move(p, d, true)
+			}
+			h.gs.loop = 1
+
 		case opSHZ0, opSHZ1:
 			top--
 			zonePointer, i, d, ok := h.displacement(opcode&1 == 0)
@@ -740,6 +758,9 @@ func (h *Hinter) run(program []byte, pCurrent, pUnhinted, pInFontUnits []Point,
 		case opNOT:
 			h.stack[top-1] = bool2int32(h.stack[top-1] == 0)
 
+		case opDELTAP1:
+			goto deltap
+
 		case opSDB:
 			top--
 			h.gs.deltaBase = h.stack[top]
@@ -794,6 +815,9 @@ func (h *Hinter) run(program []byte, pCurrent, pUnhinted, pInFontUnits []Point,
 			// This code does not implement engine compensation, as we don't expect to
 			// be used to output on dot-matrix printers.
 
+		case opDELTAP2, opDELTAP3:
+			goto deltap
+
 		case opSROUND, opS45ROUND:
 			top--
 			switch (h.stack[top] >> 6) & 0x03 {
@@ -1130,6 +1154,40 @@ func (h *Hinter) run(program []byte, pCurrent, pUnhinted, pInFontUnits []Point,
 			}
 			continue
 		}
+
+	deltap:
+		top--
+		n := f26dot6(h.stack[top])
+		if top < 2*int(h.gs.loop) {
+			return errors.New("truetype: hinting: stack underflow")
+		}
+		for ; n > 0; n-- {
+			top -= 2
+			p := h.point(0, current, h.stack[top+1])
+			if p == nil {
+				return errors.New("truetype: hinting: point out of range")
+			}
+			b := h.stack[top]
+			c := (b & 0xf0) >> 4
+			switch opcode {
+			case opDELTAP2:
+				c += 16
+			case opDELTAP3:
+				c += 32
+			}
+			c += h.gs.deltaBase
+			if ppem := (h.scale + 1<<5) >> 6; ppem != c {
+				continue
+			}
+			b = (b & 0x0f) - 8
+			if b >= 0 {
+				b++
+			}
+			b = b * 64 / (1 << uint32(h.gs.deltaShift))
+			h.move(p, f26dot6(b), true)
+		}
+		pc++
+		continue
 	}
 	return nil
 }
diff --git a/freetype/truetype/opcodes.go b/freetype/truetype/opcodes.go
index 0d467e7..bb07b7e 100644
--- a/freetype/truetype/opcodes.go
+++ b/freetype/truetype/opcodes.go
@@ -60,8 +60,8 @@ const (
 	opMDAP1     = 0x2f // .
 	opIUP0      = 0x30 // Interpolate Untouched Points through the outline
 	opIUP1      = 0x31 // .
-	opSHP0      = 0x32
-	opSHP1      = 0x33
+	opSHP0      = 0x32 // SHift Point using reference point
+	opSHP1      = 0x33 // .
 	opSHC0      = 0x34
 	opSHC1      = 0x35
 	opSHZ0      = 0x36 // SHift Zone using reference point
@@ -103,7 +103,7 @@ const (
 	opAND       = 0x5a // logical AND
 	opOR        = 0x5b // logical OR
 	opNOT       = 0x5c // logical NOT
-	opDELTAP1   = 0x5d
+	opDELTAP1   = 0x5d // DELTA exception P1
 	opSDB       = 0x5e // Set Delta Base in the graphics state
 	opSDS       = 0x5f // Set Delta Shift in the graphics state
 	opADD       = 0x60 // ADD
@@ -123,8 +123,8 @@ const (
 	opNROUND10  = 0x6e // .
 	opNROUND11  = 0x6f // .
 	opWCVTF     = 0x70
-	opDELTAP2   = 0x71
-	opDELTAP3   = 0x72
+	opDELTAP2   = 0x71 // DELTA exception P2
+	opDELTAP3   = 0x72 // DELTA exception P3
 	opDELTAC1   = 0x73
 	opDELTAC2   = 0x74
 	opDELTAC3   = 0x75
@@ -274,11 +274,11 @@ var popCount = [256]uint8{
 	0, 0, 0, 0, 0, 0, 2, 2, 2, 2, 2, 2, 0, 0, 0, q, // 0x00 - 0x0f
 	1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 0, 1, 1, 1, 1, // 0x10 - 0x1f
 	1, 1, 0, 2, 0, 1, 1, q, q, q, 2, 1, 1, 0, 1, 1, // 0x20 - 0x2f
-	0, 0, q, q, q, q, 1, 1, 1, 0, 2, 2, 0, 0, 2, 2, // 0x30 - 0x3f
+	0, 0, 0, 0, q, q, 1, 1, 1, 0, 2, 2, 0, 0, 2, 2, // 0x30 - 0x3f
 	0, 0, 2, 1, 2, 1, 1, 1, q, 2, 2, 0, 0, 0, 0, 0, // 0x40 - 0x4f
-	2, 2, 2, 2, 2, 2, 1, 1, 1, 0, 2, 2, 1, q, 1, 1, // 0x50 - 0x5f
+	2, 2, 2, 2, 2, 2, 1, 1, 1, 0, 2, 2, 1, 1, 1, 1, // 0x50 - 0x5f
 	2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x60 - 0x6f
-	q, q, q, q, q, q, 1, 1, 2, 2, 0, q, 0, 0, 1, 1, // 0x70 - 0x7f
+	q, 1, 1, q, q, q, 1, 1, 2, 2, 0, q, 0, 0, 1, 1, // 0x70 - 0x7f
 	q, q, q, q, q, 1, q, q, 1, 1, 3, 2, 2, 1, q, q, // 0x80 - 0x8f
 	q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, // 0x90 - 0x9f
 	q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, q, // 0xa0 - 0xaf
diff --git a/freetype/truetype/truetype_test.go b/freetype/truetype/truetype_test.go
index b391db3..80b0b00 100644
--- a/freetype/truetype/truetype_test.go
+++ b/freetype/truetype/truetype_test.go
@@ -253,7 +253,7 @@ var scalingTestCases = []struct {
 }{
 	{"luxisr", 12, -1},
 	{"x-arial-bold", 11, 0},
-	{"x-deja-vu-sans-oblique", 17, 5},
+	{"x-deja-vu-sans-oblique", 17, 14},
 	{"x-droid-sans-japanese", 9, 0},
 	{"x-times-new-roman", 13, 0},
 }