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/*
* Copyright (c) 2008, 2009, Google Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "third_party/blink/renderer/platform/fonts/vdmx_parser.h"
#include <stdlib.h>
#include <string.h>
#include "base/containers/span.h"
#include "base/containers/span_reader.h"
#include "base/numerics/byte_conversions.h"
#include "base/types/optional_util.h"
#include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"
namespace blink {
// VDMX parsing code.
//
// VDMX tables are found in some TrueType/OpenType fonts and contain
// ascender/descender overrides for certain (usually small) sizes. This is
// needed in order to match font metrics on Windows.
//
// Freetype does not parse these tables so we do so here.
// Parse a TrueType VDMX table.
// yMax: (output) the ascender value from the table
// yMin: (output) the descender value from the table (negative!)
// vdmx: the table bytes
// vdmxLength: length of @vdmx, in bytes
// targetPixelSize: the pixel size of the font (e.g. 16)
//
// Returns true iff a suitable match are found. Otherwise, *yMax and *yMin are
// untouched. size_t must be 32-bits to avoid overflow.
//
// See http://www.microsoft.com/opentype/otspec/vdmx.htm
bool ParseVDMX(int* y_max,
int* y_min,
const uint8_t* vdmx_ptr,
size_t vdmx_length,
unsigned target_pixel_size) {
auto vdmx =
// TODO(crbug.com/40284755): ParseVDMX should receive a span, not a
// pointer and length.
UNSAFE_TODO(base::span(vdmx_ptr, vdmx_length));
// We ignore the version. Future tables should be backwards compatible with
// this layout.
uint16_t num_ratios;
{
auto reader = base::SpanReader(vdmx);
if (!reader.Skip(4u) || !reader.ReadU16BigEndian(num_ratios)) {
return false;
}
}
const size_t ratios_offset = 6u; // Bytes read so far.
// Now we have two tables. Firstly we have @numRatios Ratio records, then a
// matching array of @numRatios offsets. We save the offset of the beginning
// of this second table.
//
// Range 6 <= x <= 262146
size_t offset_table_offset =
ratios_offset + 4u /* sizeof struct ratio */ * num_ratios;
unsigned desired_ratio = 0xffffffff;
// We read 4 bytes per record, so the offset range is
// 6 <= x <= 524286
{
auto reader = base::SpanReader(vdmx.subspan(ratios_offset));
for (unsigned i = 0; i < num_ratios; ++i) {
uint8_t x_ratio, y_ratio1, y_ratio2;
if (!reader.Skip(1u) || !reader.ReadU8BigEndian(x_ratio) ||
!reader.ReadU8BigEndian(y_ratio1) ||
!reader.ReadU8BigEndian(y_ratio2)) {
return false;
}
// This either covers 1:1, or this is the default entry (0, 0, 0)
if ((x_ratio == 1 && y_ratio1 <= 1 && y_ratio2 >= 1) ||
(x_ratio == 0 && y_ratio1 == 0 && y_ratio2 == 0)) {
desired_ratio = i;
break;
}
}
}
if (desired_ratio == 0xffffffff) // no ratio found
return false;
uint16_t group_offset;
{
// Range 10 <= x <= 393216
const size_t offset_of_group_offset =
offset_table_offset + sizeof(uint16_t) * desired_ratio;
if (offset_of_group_offset + sizeof(uint16_t) > vdmx.size()) {
return false;
}
// Now we read from the offset table to get the offset of another array.
group_offset = base::U16FromBigEndian(
vdmx.subspan(offset_of_group_offset).first<2u>());
}
{
auto reader = base::SpanReader(vdmx.subspan(
// Range 0 <= x <= 65535
group_offset));
uint16_t num_records;
if (!reader.ReadU16BigEndian(num_records) ||
!reader.Skip(sizeof(uint16_t))) {
return false;
}
// We read 6 bytes per record, so the offset range is
// 4 <= x <= 458749
for (unsigned i = 0; i < num_records; ++i) {
uint16_t pixel_size;
if (!reader.ReadU16BigEndian(pixel_size)) {
return false;
}
// the entries are sorted, so we can abort early if need be
if (pixel_size > target_pixel_size) {
return false;
}
if (pixel_size == target_pixel_size) {
int16_t temp_y_max, temp_y_min;
if (!reader.ReadI16BigEndian(temp_y_max) ||
!reader.ReadI16BigEndian(temp_y_min)) {
return false;
}
*y_min = temp_y_min;
*y_max = temp_y_max;
return true;
} else if (!reader.Skip(2 * sizeof(int16_t))) {
return false;
}
}
}
return false;
}
} // namespace blink
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