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// Copyright 2020 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "pdf/thumbnail.h"
#include <algorithm>
#include <cmath>
#include "base/check.h"
#include "base/check_op.h"
#include "base/numerics/ranges.h"
#include "base/numerics/safe_math.h"
#include "third_party/skia/include/core/SkBitmap.h"
#include "third_party/skia/include/core/SkImageInfo.h"
#include "ui/gfx/geometry/size.h"
namespace chrome_pdf {
namespace {
constexpr float kMinDevicePixelRatio = 0.25;
constexpr float kMaxDevicePixelRatio = 2;
constexpr int kImageColorChannels = 4;
// TODO( Reevaluate the thumbnail size cap when the PDF
// component migrates off of PPAPI.
// The maximum thumbnail area is essentially arbitrary, but the value was chosen
// considering the fact that when sending array buffers through PPAPI, if the
// size of the data is over 256KiB, it gets sent using shared memory instead of
// IPC. Thumbnail sizes are capped at 255KiB to avoid the 256KiB threshold for
// images and their metadata, such as size.
constexpr int kMaxThumbnailPixels = 255 * 1024 / kImageColorChannels;
// Maximum CSS dimensions are set to match UX specifications.
// These constants should be kept in sync with `PORTRAIT_WIDTH` and
// chrome/browser/resources/pdf/elements/viewer-thumbnail.js.
constexpr int kMaxWidthPortraitPx = 108;
constexpr int kMaxWidthLandscapePx = 140;
// PDF page size limits in default user space units, as defined by PDF 1.7 Annex
// C.2, "Architectural limits".
constexpr int kPdfPageMinDimension = 3;
constexpr int kPdfPageMaxDimension = 14400;
constexpr int kPdfMaxAspectRatio = kPdfPageMaxDimension / kPdfPageMinDimension;
// Limit the proportions within PDF limits to handle pathological PDF pages.
gfx::Size LimitAspectRatio(gfx::Size page_size) {
// Bump up any lengths of 0 to 1.
page_size.SetToMax(gfx::Size(1, 1));
if (page_size.height() / page_size.width() > kPdfMaxAspectRatio)
return gfx::Size(kPdfPageMinDimension, kPdfPageMaxDimension);
if (page_size.width() / page_size.height() > kPdfMaxAspectRatio)
return gfx::Size(kPdfPageMaxDimension, kPdfPageMinDimension);
return page_size;
// Calculate the size of a thumbnail image in device pixels using |page_size| in
// any units and |device_pixel_ratio|.
gfx::Size CalculateBestFitSize(const gfx::Size& page_size,
float device_pixel_ratio) {
gfx::Size safe_page_size = LimitAspectRatio(page_size);
// Return the larger of the unrotated and rotated sizes to over-sample the PDF
// page so that the thumbnail looks good in different orientations.
float scale_portrait =
static_cast<float>(kMaxWidthPortraitPx) /
std::min(safe_page_size.width(), safe_page_size.height());
float scale_landscape =
static_cast<float>(kMaxWidthLandscapePx) /
std::max(safe_page_size.width(), safe_page_size.height());
float scale = std::max(scale_portrait, scale_landscape) * device_pixel_ratio;
// Using gfx::ScaleToFlooredSize() is fine because `scale` will not yield an
// empty size unless `device_pixel_ratio` is very small (close to 0).
// However, `device_pixel_ratio` support is limited to between 0.25 and 2.
gfx::Size scaled_size = gfx::ScaleToFlooredSize(safe_page_size, scale);
if (scaled_size.GetCheckedArea().ValueOrDefault(kMaxThumbnailPixels + 1) >
kMaxThumbnailPixels) {
// Recalculate `scale` to accommodate pixel size limit such that:
// (scale * safe_page_size.width()) * (scale * safe_page_size.height()) ==
// kMaxThumbnailPixels;
scale = std::sqrt(static_cast<float>(kMaxThumbnailPixels) /
safe_page_size.width() / safe_page_size.height());
return gfx::ScaleToFlooredSize(safe_page_size, scale);
return scaled_size;
} // namespace
Thumbnail::Thumbnail() = default;
Thumbnail::Thumbnail(const gfx::Size& page_size, float device_pixel_ratio) {
DCHECK_GE(device_pixel_ratio, kMinDevicePixelRatio);
DCHECK_LE(device_pixel_ratio, kMaxDevicePixelRatio);
device_pixel_ratio_ = base::ClampToRange(
device_pixel_ratio, kMinDevicePixelRatio, kMaxDevicePixelRatio);
const gfx::Size thumbnail_size_device_pixels =
CalculateBestFitSize(page_size, device_pixel_ratio_);
// Note that <canvas> can only hold data in RGBA format. It is the
// responsibility of the thumbnail's renderer to fill `bitmap_` with RGBA
// data.
const SkImageInfo info =
kRGBA_8888_SkColorType, kPremul_SkAlphaType);
bool success = bitmap_.tryAllocPixels(info, info.minRowBytes());
Thumbnail::Thumbnail(Thumbnail&& other) = default;
Thumbnail& Thumbnail::operator=(Thumbnail&& other) = default;
Thumbnail::~Thumbnail() = default;
} // namespace chrome_pdf