405 lines
9.1 KiB
Go
405 lines
9.1 KiB
Go
// Copyright 2012 The Freetype-Go Authors. All rights reserved.
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// Use of this source code is governed by your choice of either the
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// FreeType License or the GNU General Public License version 2 (or
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// any later version), both of which can be found in the LICENSE file.
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package truetype
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// This file implements a Truetype bytecode interpreter.
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// The opcodes are described at https://developer.apple.com/fonts/TTRefMan/RM05/Chap5.html
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import (
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"errors"
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)
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type hinter struct {
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stack [800]int32
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// The graphics state is described at https://developer.apple.com/fonts/TTRefMan/RM04/Chap4.html
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roundPeriod, roundPhase, roundThreshold int32
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}
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func (h *hinter) run(program []byte) error {
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// The default rounding policy is round to grid.
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h.roundPeriod = 1 << 6
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h.roundPhase = 0
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h.roundThreshold = 1 << 5
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if len(program) > 50000 {
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return errors.New("truetype: hinting: too many instructions")
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}
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var (
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steps, pc, top int
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opcode uint8
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)
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for 0 <= pc && int(pc) < len(program) {
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steps++
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if steps == 100000 {
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return errors.New("truetype: hinting: too many steps")
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}
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opcode = program[pc]
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if popCount[opcode] == q {
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return errors.New("truetype: hinting: unimplemented instruction")
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}
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if top < int(popCount[opcode]) {
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return errors.New("truetype: hinting: stack underflow")
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}
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switch opcode {
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case opRTG:
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h.roundPeriod = 1 << 6
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h.roundPhase = 0
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h.roundThreshold = 1 << 5
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case opRTHG:
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h.roundPeriod = 1 << 6
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h.roundPhase = 1 << 5
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h.roundThreshold = 1 << 5
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case opELSE:
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opcode = 1
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goto ifelse
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case opJMPR:
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top--
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pc += int(h.stack[top])
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continue
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case opDUP:
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if int(top) >= len(h.stack) {
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return errors.New("truetype: hinting: stack overflow")
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}
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h.stack[top] = h.stack[top-1]
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top++
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case opPOP:
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top--
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case opCLEAR:
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top = 0
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case opSWAP:
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h.stack[top-1], h.stack[top-2] = h.stack[top-2], h.stack[top-1]
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case opDEPTH:
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if int(top) >= len(h.stack) {
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return errors.New("truetype: hinting: stack overflow")
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}
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h.stack[top] = int32(top)
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top++
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case opCINDEX, opMINDEX:
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x := int(h.stack[top-1])
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if x <= 0 || x >= top {
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return errors.New("truetype: hinting: invalid data")
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}
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h.stack[top-1] = h.stack[top-1-x]
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if opcode == opMINDEX {
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copy(h.stack[top-1-x:top-1], h.stack[top-x:top])
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top--
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}
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case opRTDG:
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h.roundPeriod = 1 << 5
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h.roundPhase = 0
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h.roundThreshold = 1 << 4
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case opNPUSHB:
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opcode = 0
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goto push
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case opNPUSHW:
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opcode = 0x80
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goto push
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case opDEBUG:
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// No-op.
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case opLT:
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top--
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h.stack[top-1] = bool2int32(h.stack[top-1] < h.stack[top])
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case opLTEQ:
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top--
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h.stack[top-1] = bool2int32(h.stack[top-1] <= h.stack[top])
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case opGT:
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top--
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h.stack[top-1] = bool2int32(h.stack[top-1] > h.stack[top])
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case opGTEQ:
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top--
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h.stack[top-1] = bool2int32(h.stack[top-1] >= h.stack[top])
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case opEQ:
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top--
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h.stack[top-1] = bool2int32(h.stack[top-1] == h.stack[top])
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case opNEQ:
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top--
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h.stack[top-1] = bool2int32(h.stack[top-1] != h.stack[top])
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case opAND:
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top--
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h.stack[top-1] = bool2int32(h.stack[top-1] != 0 && h.stack[top] != 0)
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case opOR:
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top--
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h.stack[top-1] = bool2int32(h.stack[top-1]|h.stack[top] != 0)
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case opNOT:
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h.stack[top-1] = bool2int32(h.stack[top-1] == 0)
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case opIF:
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top--
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if h.stack[top] == 0 {
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opcode = 0
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goto ifelse
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}
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case opEIF:
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// No-op.
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case opADD:
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top--
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h.stack[top-1] += h.stack[top]
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case opSUB:
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top--
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h.stack[top-1] -= h.stack[top]
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case opDIV:
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top--
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if h.stack[top] == 0 {
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return errors.New("truetype: hinting: division by zero")
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}
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h.stack[top-1] = div(h.stack[top-1], h.stack[top])
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case opMUL:
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top--
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h.stack[top-1] = mul(h.stack[top-1], h.stack[top])
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case opABS:
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if h.stack[top-1] < 0 {
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h.stack[top-1] = -h.stack[top-1]
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}
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case opNEG:
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h.stack[top-1] = -h.stack[top-1]
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case opFLOOR:
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h.stack[top-1] &^= 63
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case opCEILING:
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h.stack[top-1] += 63
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h.stack[top-1] &^= 63
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case opROUND00, opROUND01, opROUND10, opROUND11:
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// The four flavors of opROUND are equivalent. See the comment below on
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// opNROUND for the rationale.
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h.stack[top-1] = h.round(h.stack[top-1])
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case opNROUND00, opNROUND01, opNROUND10, opNROUND11:
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// No-op. The spec says to add one of four "compensations for the engine
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// characteristics", to cater for things like "different dot-size printers".
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// https://developer.apple.com/fonts/TTRefMan/RM02/Chap2.html#engine_compensation
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// This code does not implement engine compensation, as we don't expect to
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// be used to output on dot-matrix printers.
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case opSROUND, opS45ROUND:
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top--
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switch (h.stack[top] >> 6) & 0x03 {
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case 0:
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h.roundPeriod = 1 << 5
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case 1, 3:
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h.roundPeriod = 1 << 6
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case 2:
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h.roundPeriod = 1 << 7
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}
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if opcode == opS45ROUND {
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// The spec says to multiply by √2, but the C Freetype code says 1/√2.
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// We go with 1/√2.
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h.roundPeriod *= 46341
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h.roundPeriod /= 65536
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}
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h.roundPhase = h.roundPeriod * ((h.stack[top] >> 4) & 0x03) / 4
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if x := h.stack[top] & 0x0f; x != 0 {
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h.roundThreshold = h.roundPeriod * (x - 4) / 8
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} else {
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h.roundThreshold = h.roundPeriod - 1
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}
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case opJROT:
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top -= 2
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if h.stack[top+1] != 0 {
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pc += int(h.stack[top])
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continue
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}
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case opJROF:
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top -= 2
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if h.stack[top+1] == 0 {
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pc += int(h.stack[top])
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continue
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}
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case opROFF:
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h.roundPeriod = 0
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h.roundPhase = 0
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h.roundThreshold = 0
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case opRUTG:
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h.roundPeriod = 1 << 6
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h.roundPhase = 0
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h.roundThreshold = 1<<6 - 1
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case opRDTG:
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h.roundPeriod = 1 << 6
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h.roundPhase = 0
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h.roundThreshold = 0
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case opPUSHB000, opPUSHB001, opPUSHB010, opPUSHB011, opPUSHB100, opPUSHB101, opPUSHB110, opPUSHB111:
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opcode -= opPUSHB000 - 1
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goto push
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case opPUSHW000, opPUSHW001, opPUSHW010, opPUSHW011, opPUSHW100, opPUSHW101, opPUSHW110, opPUSHW111:
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opcode -= opPUSHW000 - 1
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opcode += 0x80
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goto push
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default:
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return errors.New("truetype: hinting: unrecognized instruction")
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}
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pc++
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continue
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ifelse:
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// Skip past bytecode until the next ELSE (if opcode == 0) or the
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// next EIF (for all opcodes). Opcode == 0 means that we have come
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// from an IF. Opcode == 1 means that we have come from an ELSE.
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{
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ifelseloop:
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for depth := 0; ; {
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pc++
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if pc >= len(program) {
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return errors.New("truetype: hinting: unbalanced IF or ELSE")
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}
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switch program[pc] {
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case opIF:
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depth++
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case opELSE:
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if depth == 0 && opcode == 0 {
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break ifelseloop
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}
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case opEIF:
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depth--
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if depth < 0 {
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break ifelseloop
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}
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case opNPUSHB:
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pc++
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if pc >= len(program) {
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return errors.New("truetype: hinting: unbalanced IF or ELSE")
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}
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pc += int(program[pc])
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case opNPUSHW:
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pc++
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if pc >= len(program) {
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return errors.New("truetype: hinting: unbalanced IF or ELSE")
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}
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pc += 2 * int(program[pc])
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case opPUSHB000, opPUSHB001, opPUSHB010, opPUSHB011, opPUSHB100, opPUSHB101, opPUSHB110, opPUSHB111:
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pc += int(program[pc] - (opPUSHB000 - 1))
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case opPUSHW000, opPUSHW001, opPUSHW010, opPUSHW011, opPUSHW100, opPUSHW101, opPUSHW110, opPUSHW111:
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pc += 2 * int(program[pc]-(opPUSHW000-1))
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default:
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// No-op.
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}
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}
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pc++
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continue
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}
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push:
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// Push n elements from the program to the stack, where n is the low 7 bits of
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// opcode. If the low 7 bits are zero, then n is the next byte from the program.
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// The high bit being 0 means that the elements are zero-extended bytes.
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// The high bit being 1 means that the elements are sign-extended words.
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{
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width := 1
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if opcode&0x80 != 0 {
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opcode &^= 0x80
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width = 2
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}
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if opcode == 0 {
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pc++
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if int(pc) >= len(program) {
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return errors.New("truetype: hinting: insufficient data")
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}
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opcode = program[pc]
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}
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pc++
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if top+int(opcode) > len(h.stack) {
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return errors.New("truetype: hinting: stack overflow")
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}
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if pc+width*int(opcode) > len(program) {
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return errors.New("truetype: hinting: insufficient data")
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}
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for ; opcode > 0; opcode-- {
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if width == 1 {
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h.stack[top] = int32(program[pc])
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} else {
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h.stack[top] = int32(int8(program[pc]))<<8 | int32(program[pc+1])
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}
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top++
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pc += width
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}
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continue
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}
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}
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return nil
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}
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// div returns x/y in 26.6 fixed point arithmetic.
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func div(x, y int32) int32 {
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return int32((int64(x) << 6) / int64(y))
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}
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// mul returns x*y in 26.6 fixed point arithmetic.
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func mul(x, y int32) int32 {
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return int32(int64(x) * int64(y) >> 6)
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}
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// round rounds the given number. The rounding algorithm is described at
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// https://developer.apple.com/fonts/TTRefMan/RM02/Chap2.html#rounding
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func (h *hinter) round(x int32) int32 {
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if h.roundPeriod == 0 {
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return x
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}
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neg := x < 0
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x -= h.roundPhase
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x += h.roundThreshold
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if x >= 0 {
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x = (x / h.roundPeriod) * h.roundPeriod
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} else {
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x -= h.roundPeriod
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x += 1
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x = (x / h.roundPeriod) * h.roundPeriod
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}
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x += h.roundPhase
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if neg {
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if x >= 0 {
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x = h.roundPhase - h.roundPeriod
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}
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} else if x < 0 {
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x = h.roundPhase
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}
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return x
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}
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func bool2int32(b bool) int32 {
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if b {
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return 1
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}
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return 0
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}
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