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add more tables to subset

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add additional optional and required (but really optional) tables to the truetype subset generated. adds cvt, fpgm and name tables to the output font file. also pads tables so they correctly appear on 4 byte boundaries.
This commit is contained in:
Eliot Jones
2020-01-04 09:43:27 +00:00
parent b15a3a9b57
commit 694388f9b6
1 changed files with 62 additions and 27 deletions
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89
src/UglyToad.PdfPig/Writer/Fonts/Subsetting/TrueTypeSubsetter.cs
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@@ -16,35 +16,45 @@
private const ushort IndexToLocLong = 1;
/*
* The PDF specification requires the following 10 tables:
* The PDF specification requires the following 9 tables:
* cmap
* glyf
* head
* hhea
* hmtx
* loca
* maxp
* cvt
* fpgm
* prep
* cmap
* But not all fonts include 'cvt ' and 'fpgm'.
* name
* post
* But not all fonts include for PDF need 'name' and 'post' tables.
*/
private static readonly IReadOnlyList<string> RequiredTags = new[]
{
TrueTypeHeaderTable.Cmap,
// TrueTypeHeaderTable.Cvt,
// TrueTypeHeaderTable.Fpgm,
TrueTypeHeaderTable.Glyf,
TrueTypeHeaderTable.Head,
TrueTypeHeaderTable.Hhea,
TrueTypeHeaderTable.Hmtx,
TrueTypeHeaderTable.Loca,
TrueTypeHeaderTable.Maxp,
TrueTypeHeaderTable.Prep
TrueTypeHeaderTable.Maxp
};
private static readonly TrueTypeFontParser Parser
= new TrueTypeFontParser();
/// <summary>
/// The tags for tables which are optional or required but can be skipped for PDF.
/// This should also include hdmx, kern and OS/2 tables.
/// </summary>
private static readonly IReadOnlyList<string> OptionalTags = new[]
{
TrueTypeHeaderTable.Cvt,
TrueTypeHeaderTable.Fpgm,
TrueTypeHeaderTable.Prep,
TrueTypeHeaderTable.Name,
// TrueTypeHeaderTable.Post
};
private static readonly byte[] PaddingBytes = {0, 0, 0, 0};
private static readonly TrueTypeFontParser Parser = new TrueTypeFontParser();
public static byte[] Subset(byte[] fontBytes, TrueTypeSubsetEncoding newEncoding)
{
@@ -62,29 +72,48 @@
var indexMapping = GetIndexMapping(font, newEncoding);
var directoryEntries = new DirectoryEntry[RequiredTags.Count];
using (var stream = new MemoryStream())
{
var offsetSubtable = new TrueTypeOffsetSubtable((byte)RequiredTags.Count);
offsetSubtable.Write(stream);
var copiedTableTags = new SortedSet<string>(StringComparer.Ordinal);
// The table directory follows the offset subtable.
// Entries in the table directory must be sorted in ascending order by tag (case sensitive).
// Each table in the font file must have its own table directory entry.
for (var i = 0; i < RequiredTags.Count; i++)
{
var tag = RequiredTags[i];
if (!font.TableHeaders.TryGetValue(tag, out var inputHeader))
if (!font.TableHeaders.ContainsKey(tag))
{
throw new InvalidFontFormatException($"Font does not contain table required for subsetting: {tag}.");
}
var entry = new DirectoryEntry(tag, stream.Position, inputHeader);
copiedTableTags.Add(tag);
}
for (var i = 0; i < OptionalTags.Count; i++)
{
var tag = OptionalTags[i];
if (!font.TableHeaders.ContainsKey(tag))
{
continue;
}
copiedTableTags.Add(tag);
}
var offsetSubtable = new TrueTypeOffsetSubtable((byte)copiedTableTags.Count);
offsetSubtable.Write(stream);
// The table directory follows the offset subtable.
var directoryEntries = new DirectoryEntry[copiedTableTags.Count];
// Entries in the table directory must be sorted in ascending order by tag (case sensitive).
// Each table in the font file must have its own table directory entry.
var index = 0;
foreach (var tag in copiedTableTags)
{
var entry = new DirectoryEntry(tag, stream.Position, font.TableHeaders[tag]);
entry.DummyHeader.Write(stream);
directoryEntries[i] = entry;
directoryEntries[index++] = entry;
}
// Generate the glyph subset.
@@ -94,9 +123,7 @@
for (var i = 0; i < directoryEntries.Length; i++)
{
var entry = directoryEntries[i];
// TODO: place on a % 4 boundary offset.
entry.OutputTableOffset = stream.Position;
if (entry.Tag == TrueTypeHeaderTable.Cmap)
@@ -150,6 +177,14 @@
}
entry.Length = (uint)(stream.Position - entry.OutputTableOffset);
// Tables must start on 4 byte boundaries.
var remainder = stream.Position % 4;
if (remainder > 0)
{
var toAppend = 4 - remainder;
stream.Write(PaddingBytes, 0, (int)toAppend);
}
}
using (var inputBytes = new StreamInputBytes(stream, false))
@@ -216,7 +251,7 @@
}
}
var cmap = new CMapTable(font.TableRegister.CMapTable.Version, entry.DummyHeader, new []
var cmap = new CMapTable(font.TableRegister.CMapTable.Version, entry.DummyHeader, new[]
{
new ByteEncodingCMapTable(TrueTypeCMapPlatform.Macintosh, 0, 0, data)
});