vhea.lisp

   1 ;;; Copyright (c) 2024 Daniel Kochmański, All Rights Reserved
   2 ;;;
   3 ;;; Redistribution and use in source and binary forms, with or without
   4 ;;; modification, are permitted provided that the following conditions
   5 ;;; are met:
   6 ;;;
   7 ;;;   * Redistributions of source code must retain the above copyright
   8 ;;;     notice, this list of conditions and the following disclaimer.
   9 ;;;
  10 ;;;   * Redistributions in binary form must reproduce the above
  11 ;;;     copyright notice, this list of conditions and the following
  12 ;;;     disclaimer in the documentation and/or other materials
  13 ;;;     provided with the distribution.
  14 ;;;
  15 ;;; THIS SOFTWARE IS PROVIDED BY THE AUTHOR 'AS IS' AND ANY EXPRESSED
  16 ;;; OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  17 ;;; WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  18 ;;; ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
  19 ;;; DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  20 ;;; DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
  21 ;;; GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  22 ;;; INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
  23 ;;; WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  24 ;;; NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  25 ;;; SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  26 ;;;
  27 ;;; Loading data from the "vhea" table.
  28 ;;;
  29 ;;;  https://learn.microsoft.com/en-us/typography/opentype/spec/vhea
  30 ;;;  https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6vhea.html
  31 ;;;
  32
  33 (in-package #:zpb-ttf)
  34
  35 ;;; Tables 'vhea' and 'vmtx' are not present in some fonts. For that reason we
  36 ;;; have a fallback where metrics are supplanted with default values based on
  37 ;;; horizontal metrics.
  38
  39 (defmethod load-vhea-info ((font-loader font-loader))
  40   (unless (table-info "vhea" font-loader)
  41     (setf (vhea-missing-p font-loader) t)
  42     (let ((dx (/ (max-width font-loader) 2)))
  43       (with-slots (vascender vdescender)
  44           font-loader
  45         (setf vascender dx
  46               vdescender (- dx))))
  47     (return-from load-vhea-info))
  48   (seek-to-table "vhea" font-loader)
  49   (with-slots (input-stream vascender vdescender)
  50       font-loader
  51     (let ((version (read-fixed input-stream)))
  52       (check-version "\"vhea\" table" version #x00010000 #x00011000))
  53     (setf vascender (read-fword input-stream)
  54           vdescender (read-fword input-stream))))
  55
  56 (defmethod vertical-metrics-count ((font-loader font-loader))
  57   (when (or (vhea-missing-p font-loader)
  58             (null (table-info "vhea" font-loader)))
  59     ;; (warn "Table 'vhea' is missing.")
  60     (setf (vhea-missing-p font-loader) t)
  61     (return-from vertical-metrics-count))
  62   (seek-to-table "vhea" font-loader)
  63   (with-slots (input-stream) font-loader
  64     ;; Skip to the end, since all we care about is the last item
  65     (advance-file-position input-stream 34)
  66     (read-uint16 input-stream)))