vmtx.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 ;;;
  28 ;;; Loading data from the 'vmtx' table.
  29 ;;;
  30 ;;;  https://learn.microsoft.com/en-us/typography/opentype/spec/vmtx
  31 ;;;  https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6vmtx.html
  32 ;;;
  33
  34 (in-package #:zpb-ttf)
  35
  36 ;;; Tables 'vhea' and 'vmtx' are not present in some fonts. For that reason we
  37 ;;; have a fallback where metrics are supplanted with default values based on
  38 ;;; horizontal metrics.
  39
  40 (defmethod load-vmtx-info ((font-loader font-loader))
  41   (when (or (vhea-missing-p font-loader)
  42             (null (table-info "vmtx" font-loader)))
  43     (setf (vmtx-missing-p font-loader) t)
  44     (let ((line-height (- (ascender font-loader) (descender font-loader))))
  45       ;; TOP-SIDE-BEARING depends on individual glyph metric YMAX.
  46       (setf (advance-heights font-loader)
  47             (make-array 1 :initial-element line-height)))
  48     (return-from load-vmtx-info))
  49   (let* ((vertical-metrics-count (vertical-metrics-count font-loader))
  50          (advance-heights (make-array vertical-metrics-count))
  51          (top-side-bearings (make-array vertical-metrics-count)))
  52     (seek-to-table "vmtx" font-loader)
  53     (with-slots (input-stream) font-loader
  54       (dotimes (i vertical-metrics-count)
  55         (setf (svref advance-heights i) (read-uint16 input-stream))
  56         (setf (svref top-side-bearings i) (read-int16 input-stream))))
  57     (setf (advance-heights font-loader) advance-heights
  58           (top-side-bearings font-loader) top-side-bearings)))