freetype/truetype: implement MSIRP instruction.

R=golang-dev, nigeltao, bsiegert
CC=golang-dev
https://codereview.appspot.com/16630044

Committer: Nigel Tao <nigeltao@golang.org>

freetype/truetype/hint.go

@@ -550,6 +550,29 @@ func (h *Hinter) run(program []byte, pCurrent, pUnhinted, pInFontUnits []Point,
 			}
 			h.gs.loop = 1
 
+		case opMSIRP0, opMSIRP1:
+			top -= 2
+			i := h.stack[top]
+			distance := f26dot6(h.stack[top+1])
+
+			// TODO: special case h.gs.zp[1] == 0 in C Freetype.
+			ref := h.point(0, current, h.gs.rp[0])
+			p := h.point(1, current, i)
+			if ref == nil || p == nil {
+				return errors.New("truetype: hinting: point out of range")
+			}
+			curDist := dotProduct(f26dot6(p.X-ref.X), f26dot6(p.Y-ref.Y), h.gs.dv)
+
+			// Set-RP0 bit.
+			if opcode == opMSIRP1 {
+				h.gs.rp[0] = i
+			}
+			h.gs.rp[1] = h.gs.rp[0]
+			h.gs.rp[2] = i
+
+			// Move the point.
+			h.move(p, distance-curDist, true)
+
 		case opALIGNRP:
 			if top < int(h.gs.loop) {
 				return errors.New("truetype: hinting: stack underflow")

freetype/truetype/opcodes.go

@@ -68,8 +68,8 @@ const (
 	opSHZ1      = 0x37 // .
 	opSHPIX     = 0x38 // SHift point by a PIXel amount
 	opIP        = 0x39 // Interpolate Point
-	opMSIRP0    = 0x3a
-	opMSIRP1    = 0x3b
+	opMSIRP0    = 0x3a // Move Stack Indirect Relative Point
+	opMSIRP1    = 0x3b // .
 	opALIGNRP   = 0x3c // ALIGN to Reference Point
 	opRTDG      = 0x3d // Round To Double Grid
 	opMIAP0     = 0x3e // Move Indirect Absolute Point
@@ -274,7 +274,7 @@ 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, q, q, 0, 0, 2, 2, // 0x30 - 0x3f
+	0, 0, q, q, 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, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x60 - 0x6f