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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/ui/thumbnail.h"
- #include <stddef.h>
- #include <algorithm>
- #include <cmath>
- #include <utility>
- #include "base/check.h"
- #include "base/check_op.h"
- #include "base/cxx17_backports.h"
- #include "base/numerics/checked_math.h"
- #include "base/values.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(crbug.com/702993): 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
- // `LANDSCAPE_WIDTH` in
- // chrome/browser/resources/pdf/elements/viewer-thumbnail.ts.
- 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;
- }
- int CalculateStride(int width) {
- base::CheckedNumeric<size_t> stride = kImageColorChannels;
- stride *= width;
- return stride.ValueOrDie<int>();
- }
- size_t CalculateImageDataSize(int stride, int height) {
- base::CheckedNumeric<int> size = stride;
- size *= height;
- return size.ValueOrDie<size_t>();
- }
- } // namespace
- Thumbnail::Thumbnail(const gfx::Size& page_size, float device_pixel_ratio)
- : device_pixel_ratio_(base::clamp(device_pixel_ratio,
- kMinDevicePixelRatio,
- kMaxDevicePixelRatio)),
- image_size_(CalculateBestFitSize(page_size, device_pixel_ratio_)),
- stride_(CalculateStride(image_size_.width())),
- image_data_(CalculateImageDataSize(stride(), image_size().height())) {
- DCHECK(!image_data_.empty());
- }
- Thumbnail::Thumbnail(Thumbnail&& other) = default;
- Thumbnail& Thumbnail::operator=(Thumbnail&& other) = default;
- Thumbnail::~Thumbnail() = default;
- base::Value::BlobStorage& Thumbnail::GetImageData() {
- DCHECK(!image_data_.empty());
- return image_data_;
- }
- base::Value::BlobStorage Thumbnail::TakeData() {
- DCHECK(!image_data_.empty());
- return std::move(image_data_);
- }
- } // namespace chrome_pdf
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