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-rw-r--r--dom/base/ResponsiveImageSelector.cpp730
1 files changed, 730 insertions, 0 deletions
diff --git a/dom/base/ResponsiveImageSelector.cpp b/dom/base/ResponsiveImageSelector.cpp
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+++ b/dom/base/ResponsiveImageSelector.cpp
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/ResponsiveImageSelector.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/PresShellInlines.h"
+#include "mozilla/ServoStyleSetInlines.h"
+#include "mozilla/TextUtils.h"
+#include "nsIURI.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/DocumentInlines.h"
+#include "nsContentUtils.h"
+#include "nsPresContext.h"
+
+#include "nsCSSProps.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION(ResponsiveImageSelector, mOwnerNode)
+
+static bool ParseInteger(const nsAString& aString, int32_t& aInt) {
+ nsContentUtils::ParseHTMLIntegerResultFlags parseResult;
+ aInt = nsContentUtils::ParseHTMLInteger(aString, &parseResult);
+ return !(parseResult &
+ (nsContentUtils::eParseHTMLInteger_Error |
+ nsContentUtils::eParseHTMLInteger_DidNotConsumeAllInput |
+ nsContentUtils::eParseHTMLInteger_NonStandard));
+}
+
+static bool ParseFloat(const nsAString& aString, double& aDouble) {
+ // Check if it is a valid floating-point number first since the result of
+ // nsString.ToDouble() is more lenient than the spec,
+ // https://html.spec.whatwg.org/#valid-floating-point-number
+ nsAString::const_iterator iter, end;
+ aString.BeginReading(iter);
+ aString.EndReading(end);
+
+ if (iter == end) {
+ return false;
+ }
+
+ if (*iter == char16_t('-') && ++iter == end) {
+ return false;
+ }
+
+ if (IsAsciiDigit(*iter)) {
+ for (; iter != end && IsAsciiDigit(*iter); ++iter)
+ ;
+ } else if (*iter == char16_t('.')) {
+ // Do nothing, jumps to fraction part
+ } else {
+ return false;
+ }
+
+ // Fraction
+ if (*iter == char16_t('.')) {
+ ++iter;
+ if (iter == end || !IsAsciiDigit(*iter)) {
+ // U+002E FULL STOP character (.) must be followed by one or more ASCII
+ // digits
+ return false;
+ }
+
+ for (; iter != end && IsAsciiDigit(*iter); ++iter)
+ ;
+ }
+
+ if (iter != end && (*iter == char16_t('e') || *iter == char16_t('E'))) {
+ ++iter;
+ if (*iter == char16_t('-') || *iter == char16_t('+')) {
+ ++iter;
+ }
+
+ if (iter == end || !IsAsciiDigit(*iter)) {
+ // Should have one or more ASCII digits
+ return false;
+ }
+
+ for (; iter != end && IsAsciiDigit(*iter); ++iter)
+ ;
+ }
+
+ if (iter != end) {
+ return false;
+ }
+
+ nsresult rv;
+ aDouble = PromiseFlatString(aString).ToDouble(&rv);
+ return NS_SUCCEEDED(rv);
+}
+
+ResponsiveImageSelector::ResponsiveImageSelector(nsIContent* aContent)
+ : mOwnerNode(aContent), mSelectedCandidateIndex(-1) {}
+
+ResponsiveImageSelector::ResponsiveImageSelector(dom::Document* aDocument)
+ : mOwnerNode(aDocument), mSelectedCandidateIndex(-1) {}
+
+ResponsiveImageSelector::~ResponsiveImageSelector() = default;
+
+void ResponsiveImageSelector::ParseSourceSet(
+ const nsAString& aSrcSet,
+ FunctionRef<void(ResponsiveImageCandidate&&)> aCallback) {
+ nsAString::const_iterator iter, end;
+ aSrcSet.BeginReading(iter);
+ aSrcSet.EndReading(end);
+
+ // Read URL / descriptor pairs
+ while (iter != end) {
+ nsAString::const_iterator url, urlEnd, descriptor;
+
+ // Skip whitespace and commas.
+ // Extra commas at this point are a non-fatal syntax error.
+ for (; iter != end &&
+ (nsContentUtils::IsHTMLWhitespace(*iter) || *iter == char16_t(','));
+ ++iter)
+ ;
+
+ if (iter == end) {
+ break;
+ }
+
+ url = iter;
+
+ // Find end of url
+ for (; iter != end && !nsContentUtils::IsHTMLWhitespace(*iter); ++iter)
+ ;
+
+ // Omit trailing commas from URL.
+ // Multiple commas are a non-fatal error.
+ while (iter != url) {
+ if (*(--iter) != char16_t(',')) {
+ iter++;
+ break;
+ }
+ }
+
+ const nsDependentSubstring& urlStr = Substring(url, iter);
+
+ MOZ_ASSERT(url != iter, "Shouldn't have empty URL at this point");
+
+ ResponsiveImageCandidate candidate;
+ if (candidate.ConsumeDescriptors(iter, end)) {
+ candidate.SetURLSpec(urlStr);
+ aCallback(std::move(candidate));
+ }
+ }
+}
+
+// http://www.whatwg.org/specs/web-apps/current-work/#processing-the-image-candidates
+bool ResponsiveImageSelector::SetCandidatesFromSourceSet(
+ const nsAString& aSrcSet, nsIPrincipal* aTriggeringPrincipal) {
+ ClearSelectedCandidate();
+
+ if (!mOwnerNode || !mOwnerNode->GetBaseURI()) {
+ MOZ_ASSERT(false, "Should not be parsing SourceSet without a document");
+ return false;
+ }
+
+ mCandidates.Clear();
+
+ auto eachCandidate = [&](ResponsiveImageCandidate&& aCandidate) {
+ aCandidate.SetTriggeringPrincipal(
+ nsContentUtils::GetAttrTriggeringPrincipal(
+ Content(), aCandidate.URLString(), aTriggeringPrincipal));
+ AppendCandidateIfUnique(std::move(aCandidate));
+ };
+
+ ParseSourceSet(aSrcSet, eachCandidate);
+
+ bool parsedCandidates = !mCandidates.IsEmpty();
+
+ // Re-add default to end of list
+ MaybeAppendDefaultCandidate();
+
+ return parsedCandidates;
+}
+
+uint32_t ResponsiveImageSelector::NumCandidates(bool aIncludeDefault) {
+ uint32_t candidates = mCandidates.Length();
+
+ // If present, the default candidate is the last item
+ if (!aIncludeDefault && candidates && mCandidates.LastElement().IsDefault()) {
+ candidates--;
+ }
+
+ return candidates;
+}
+
+nsIContent* ResponsiveImageSelector::Content() {
+ return mOwnerNode->IsContent() ? mOwnerNode->AsContent() : nullptr;
+}
+
+dom::Document* ResponsiveImageSelector::Document() {
+ return mOwnerNode->OwnerDoc();
+}
+
+void ResponsiveImageSelector::SetDefaultSource(const nsAString& aURLString,
+ nsIPrincipal* aPrincipal) {
+ ClearSelectedCandidate();
+
+ // Check if the last element of our candidates is a default
+ if (!mCandidates.IsEmpty() && mCandidates.LastElement().IsDefault()) {
+ mCandidates.RemoveLastElement();
+ }
+
+ mDefaultSourceURL = aURLString;
+ mDefaultSourceTriggeringPrincipal = aPrincipal;
+
+ // Add new default to end of list
+ MaybeAppendDefaultCandidate();
+}
+
+void ResponsiveImageSelector::ClearSelectedCandidate() {
+ mSelectedCandidateIndex = -1;
+ mSelectedCandidateURL = nullptr;
+}
+
+bool ResponsiveImageSelector::SetSizesFromDescriptor(const nsAString& aSizes) {
+ ClearSelectedCandidate();
+
+ NS_ConvertUTF16toUTF8 sizes(aSizes);
+ mServoSourceSizeList.reset(Servo_SourceSizeList_Parse(&sizes));
+ return !!mServoSourceSizeList;
+}
+
+void ResponsiveImageSelector::AppendCandidateIfUnique(
+ ResponsiveImageCandidate&& aCandidate) {
+ int numCandidates = mCandidates.Length();
+
+ // With the exception of Default, which should not be added until we are done
+ // building the list.
+ if (aCandidate.IsDefault()) {
+ return;
+ }
+
+ // Discard candidates with identical parameters, they will never match
+ for (int i = 0; i < numCandidates; i++) {
+ if (mCandidates[i].HasSameParameter(aCandidate)) {
+ return;
+ }
+ }
+
+ mCandidates.AppendElement(std::move(aCandidate));
+}
+
+void ResponsiveImageSelector::MaybeAppendDefaultCandidate() {
+ if (mDefaultSourceURL.IsEmpty()) {
+ return;
+ }
+
+ int numCandidates = mCandidates.Length();
+
+ // https://html.spec.whatwg.org/multipage/embedded-content.html#update-the-source-set
+ // step 4.1.3:
+ // If child has a src attribute whose value is not the empty string and source
+ // set does not contain an image source with a density descriptor value of 1,
+ // and no image source with a width descriptor, append child's src attribute
+ // value to source set.
+ for (int i = 0; i < numCandidates; i++) {
+ if (mCandidates[i].IsComputedFromWidth()) {
+ return;
+ } else if (mCandidates[i].Density(this) == 1.0) {
+ return;
+ }
+ }
+
+ ResponsiveImageCandidate defaultCandidate;
+ defaultCandidate.SetParameterDefault();
+ defaultCandidate.SetURLSpec(mDefaultSourceURL);
+ defaultCandidate.SetTriggeringPrincipal(mDefaultSourceTriggeringPrincipal);
+ // We don't use MaybeAppend since we want to keep this even if it can never
+ // match, as it may if the source set changes.
+ mCandidates.AppendElement(std::move(defaultCandidate));
+}
+
+already_AddRefed<nsIURI> ResponsiveImageSelector::GetSelectedImageURL() {
+ SelectImage();
+
+ nsCOMPtr<nsIURI> url = mSelectedCandidateURL;
+ return url.forget();
+}
+
+bool ResponsiveImageSelector::GetSelectedImageURLSpec(nsAString& aResult) {
+ SelectImage();
+
+ if (mSelectedCandidateIndex == -1) {
+ return false;
+ }
+
+ aResult.Assign(mCandidates[mSelectedCandidateIndex].URLString());
+ return true;
+}
+
+double ResponsiveImageSelector::GetSelectedImageDensity() {
+ int bestIndex = GetSelectedCandidateIndex();
+ if (bestIndex < 0) {
+ return 1.0;
+ }
+
+ return mCandidates[bestIndex].Density(this);
+}
+
+nsIPrincipal* ResponsiveImageSelector::GetSelectedImageTriggeringPrincipal() {
+ int bestIndex = GetSelectedCandidateIndex();
+ if (bestIndex < 0) {
+ return nullptr;
+ }
+
+ return mCandidates[bestIndex].TriggeringPrincipal();
+}
+
+bool ResponsiveImageSelector::SelectImage(bool aReselect) {
+ if (!aReselect && mSelectedCandidateIndex != -1) {
+ // Already have selection
+ return false;
+ }
+
+ int oldBest = mSelectedCandidateIndex;
+ ClearSelectedCandidate();
+
+ int numCandidates = mCandidates.Length();
+ if (!numCandidates) {
+ return oldBest != -1;
+ }
+
+ dom::Document* doc = Document();
+ nsPresContext* pctx = doc->GetPresContext();
+ nsCOMPtr<nsIURI> baseURI = mOwnerNode->GetBaseURI();
+
+ if (!pctx || !baseURI) {
+ return oldBest != -1;
+ }
+
+ double displayDensity = pctx->CSSPixelsToDevPixels(1.0f);
+ double overrideDPPX = pctx->GetOverrideDPPX();
+
+ if (overrideDPPX > 0) {
+ displayDensity = overrideDPPX;
+ }
+
+ // Per spec, "In a UA-specific manner, choose one image source"
+ // - For now, select the lowest density greater than displayDensity, otherwise
+ // the greatest density available
+
+ // If the list contains computed width candidates, compute the current
+ // effective image width.
+ double computedWidth = -1;
+ for (int i = 0; i < numCandidates; i++) {
+ if (mCandidates[i].IsComputedFromWidth()) {
+ DebugOnly<bool> computeResult =
+ ComputeFinalWidthForCurrentViewport(&computedWidth);
+ MOZ_ASSERT(computeResult,
+ "Computed candidates not allowed without sizes data");
+ break;
+ }
+ }
+
+ int bestIndex = -1;
+ double bestDensity = -1.0;
+ for (int i = 0; i < numCandidates; i++) {
+ double candidateDensity = (computedWidth == -1)
+ ? mCandidates[i].Density(this)
+ : mCandidates[i].Density(computedWidth);
+ // - If bestIndex is below display density, pick anything larger.
+ // - Otherwise, prefer if less dense than bestDensity but still above
+ // displayDensity.
+ if (bestIndex == -1 ||
+ (bestDensity < displayDensity && candidateDensity > bestDensity) ||
+ (candidateDensity >= displayDensity &&
+ candidateDensity < bestDensity)) {
+ bestIndex = i;
+ bestDensity = candidateDensity;
+ }
+ }
+
+ MOZ_ASSERT(bestIndex >= 0 && bestIndex < numCandidates);
+
+ // Resolve URL
+ nsresult rv;
+ const nsAString& urlStr = mCandidates[bestIndex].URLString();
+ nsCOMPtr<nsIURI> candidateURL;
+ rv = nsContentUtils::NewURIWithDocumentCharset(getter_AddRefs(candidateURL),
+ urlStr, doc, baseURI);
+
+ mSelectedCandidateURL = NS_SUCCEEDED(rv) ? candidateURL : nullptr;
+ mSelectedCandidateIndex = bestIndex;
+
+ return mSelectedCandidateIndex != oldBest;
+}
+
+int ResponsiveImageSelector::GetSelectedCandidateIndex() {
+ SelectImage();
+
+ return mSelectedCandidateIndex;
+}
+
+bool ResponsiveImageSelector::ComputeFinalWidthForCurrentViewport(
+ double* aWidth) {
+ dom::Document* doc = Document();
+ PresShell* presShell = doc->GetPresShell();
+ nsPresContext* pctx = presShell ? presShell->GetPresContext() : nullptr;
+
+ if (!pctx) {
+ return false;
+ }
+ nscoord effectiveWidth =
+ presShell->StyleSet()->EvaluateSourceSizeList(mServoSourceSizeList.get());
+
+ *aWidth =
+ nsPresContext::AppUnitsToDoubleCSSPixels(std::max(effectiveWidth, 0));
+ return true;
+}
+
+ResponsiveImageCandidate::ResponsiveImageCandidate() {
+ mType = CandidateType::Invalid;
+ mValue.mDensity = 1.0;
+}
+
+void ResponsiveImageCandidate::SetURLSpec(const nsAString& aURLString) {
+ mURLString = aURLString;
+}
+
+void ResponsiveImageCandidate::SetTriggeringPrincipal(
+ nsIPrincipal* aPrincipal) {
+ mTriggeringPrincipal = aPrincipal;
+}
+
+void ResponsiveImageCandidate::SetParameterAsComputedWidth(int32_t aWidth) {
+ mType = CandidateType::ComputedFromWidth;
+ mValue.mWidth = aWidth;
+}
+
+void ResponsiveImageCandidate::SetParameterDefault() {
+ MOZ_ASSERT(!IsValid(), "double setting candidate type");
+
+ mType = CandidateType::Default;
+ // mValue shouldn't actually be used for this type, but set it to default
+ // anyway
+ mValue.mDensity = 1.0;
+}
+
+void ResponsiveImageCandidate::SetParameterInvalid() {
+ mType = CandidateType::Invalid;
+ // mValue shouldn't actually be used for this type, but set it to default
+ // anyway
+ mValue.mDensity = 1.0;
+}
+
+void ResponsiveImageCandidate::SetParameterAsDensity(double aDensity) {
+ MOZ_ASSERT(!IsValid(), "double setting candidate type");
+
+ mType = CandidateType::Density;
+ mValue.mDensity = aDensity;
+}
+
+// Represents all supported descriptors for a ResponsiveImageCandidate, though
+// there is no candidate type that uses all of these. This should generally
+// match the mValue union of ResponsiveImageCandidate.
+struct ResponsiveImageDescriptors {
+ ResponsiveImageDescriptors() : mInvalid(false){};
+
+ Maybe<double> mDensity;
+ Maybe<int32_t> mWidth;
+ // We don't support "h" descriptors yet and they are not spec'd, but the
+ // current spec does specify that they can be silently ignored (whereas
+ // entirely unknown descriptors cause us to invalidate the candidate)
+ //
+ // If we ever start honoring them we should serialize them in
+ // AppendDescriptors.
+ Maybe<int32_t> mFutureCompatHeight;
+ // If this descriptor set is bogus, e.g. a value was added twice (and thus
+ // dropped) or an unknown descriptor was added.
+ bool mInvalid;
+
+ void AddDescriptor(const nsAString& aDescriptor);
+ bool Valid();
+ // Use the current set of descriptors to configure a candidate
+ void FillCandidate(ResponsiveImageCandidate& aCandidate);
+};
+
+// Try to parse a single descriptor from a string. If value already set or
+// unknown, sets invalid flag.
+// This corresponds to the descriptor "Descriptor parser" step in:
+// https://html.spec.whatwg.org/#parse-a-srcset-attribute
+void ResponsiveImageDescriptors::AddDescriptor(const nsAString& aDescriptor) {
+ if (aDescriptor.IsEmpty()) {
+ return;
+ }
+
+ // All currently supported descriptors end with an identifying character.
+ nsAString::const_iterator descStart, descType;
+ aDescriptor.BeginReading(descStart);
+ aDescriptor.EndReading(descType);
+ descType--;
+ const nsDependentSubstring& valueStr = Substring(descStart, descType);
+ if (*descType == char16_t('w')) {
+ int32_t possibleWidth;
+ // If the value is not a valid non-negative integer, it doesn't match this
+ // descriptor, fall through.
+ if (ParseInteger(valueStr, possibleWidth) && possibleWidth >= 0) {
+ if (possibleWidth != 0 && mWidth.isNothing() && mDensity.isNothing()) {
+ mWidth.emplace(possibleWidth);
+ } else {
+ // Valid width descriptor, but width or density were already seen, sizes
+ // support isn't enabled, or it parsed to 0, which is an error per spec
+ mInvalid = true;
+ }
+
+ return;
+ }
+ } else if (*descType == char16_t('h')) {
+ int32_t possibleHeight;
+ // If the value is not a valid non-negative integer, it doesn't match this
+ // descriptor, fall through.
+ if (ParseInteger(valueStr, possibleHeight) && possibleHeight >= 0) {
+ if (possibleHeight != 0 && mFutureCompatHeight.isNothing() &&
+ mDensity.isNothing()) {
+ mFutureCompatHeight.emplace(possibleHeight);
+ } else {
+ // Valid height descriptor, but height or density were already seen, or
+ // it parsed to zero, which is an error per spec
+ mInvalid = true;
+ }
+
+ return;
+ }
+ } else if (*descType == char16_t('x')) {
+ // If the value is not a valid floating point number, it doesn't match this
+ // descriptor, fall through.
+ double possibleDensity = 0.0;
+ if (ParseFloat(valueStr, possibleDensity)) {
+ if (possibleDensity >= 0.0 && mWidth.isNothing() &&
+ mDensity.isNothing() && mFutureCompatHeight.isNothing()) {
+ mDensity.emplace(possibleDensity);
+ } else {
+ // Valid density descriptor, but height or width or density were already
+ // seen, or it parsed to less than zero, which is an error per spec
+ mInvalid = true;
+ }
+
+ return;
+ }
+ }
+
+ // Matched no known descriptor, mark this descriptor set invalid
+ mInvalid = true;
+}
+
+bool ResponsiveImageDescriptors::Valid() {
+ return !mInvalid && !(mFutureCompatHeight.isSome() && mWidth.isNothing());
+}
+
+void ResponsiveImageDescriptors::FillCandidate(
+ ResponsiveImageCandidate& aCandidate) {
+ if (!Valid()) {
+ aCandidate.SetParameterInvalid();
+ } else if (mWidth.isSome()) {
+ MOZ_ASSERT(mDensity.isNothing()); // Shouldn't be valid
+
+ aCandidate.SetParameterAsComputedWidth(*mWidth);
+ } else if (mDensity.isSome()) {
+ MOZ_ASSERT(mWidth.isNothing()); // Shouldn't be valid
+
+ aCandidate.SetParameterAsDensity(*mDensity);
+ } else {
+ // A valid set of descriptors with no density nor width (e.g. an empty set)
+ // becomes 1.0 density, per spec
+ aCandidate.SetParameterAsDensity(1.0);
+ }
+}
+
+bool ResponsiveImageCandidate::ConsumeDescriptors(
+ nsAString::const_iterator& aIter,
+ const nsAString::const_iterator& aIterEnd) {
+ nsAString::const_iterator& iter = aIter;
+ const nsAString::const_iterator& end = aIterEnd;
+
+ bool inParens = false;
+
+ ResponsiveImageDescriptors descriptors;
+
+ // Parse descriptor list.
+ // This corresponds to the descriptor parsing loop from:
+ // https://html.spec.whatwg.org/#parse-a-srcset-attribute
+
+ // Skip initial whitespace
+ for (; iter != end && nsContentUtils::IsHTMLWhitespace(*iter); ++iter)
+ ;
+
+ nsAString::const_iterator currentDescriptor = iter;
+
+ for (;; iter++) {
+ if (iter == end) {
+ descriptors.AddDescriptor(Substring(currentDescriptor, iter));
+ break;
+ } else if (inParens) {
+ if (*iter == char16_t(')')) {
+ inParens = false;
+ }
+ } else {
+ if (*iter == char16_t(',')) {
+ // End of descriptors, flush current descriptor and advance past comma
+ // before breaking
+ descriptors.AddDescriptor(Substring(currentDescriptor, iter));
+ iter++;
+ break;
+ }
+ if (nsContentUtils::IsHTMLWhitespace(*iter)) {
+ // End of current descriptor, consume it, skip spaces
+ // ("After descriptor" state in spec) before continuing
+ descriptors.AddDescriptor(Substring(currentDescriptor, iter));
+ for (; iter != end && nsContentUtils::IsHTMLWhitespace(*iter); ++iter)
+ ;
+ if (iter == end) {
+ break;
+ }
+ currentDescriptor = iter;
+ // Leave one whitespace so the loop advances to this position next
+ // iteration
+ iter--;
+ } else if (*iter == char16_t('(')) {
+ inParens = true;
+ }
+ }
+ }
+
+ descriptors.FillCandidate(*this);
+
+ return IsValid();
+}
+
+bool ResponsiveImageCandidate::HasSameParameter(
+ const ResponsiveImageCandidate& aOther) const {
+ if (aOther.mType != mType) {
+ return false;
+ }
+
+ if (mType == CandidateType::Default) {
+ return true;
+ }
+
+ if (mType == CandidateType::Density) {
+ return aOther.mValue.mDensity == mValue.mDensity;
+ }
+
+ if (mType == CandidateType::Invalid) {
+ MOZ_ASSERT_UNREACHABLE("Comparing invalid candidates?");
+ return true;
+ }
+
+ if (mType == CandidateType::ComputedFromWidth) {
+ return aOther.mValue.mWidth == mValue.mWidth;
+ }
+
+ MOZ_ASSERT(false, "Somebody forgot to check for all uses of this enum");
+ return false;
+}
+
+double ResponsiveImageCandidate::Density(
+ ResponsiveImageSelector* aSelector) const {
+ if (mType == CandidateType::ComputedFromWidth) {
+ double width;
+ if (!aSelector->ComputeFinalWidthForCurrentViewport(&width)) {
+ return 1.0;
+ }
+ return Density(width);
+ }
+
+ // Other types don't need matching width
+ MOZ_ASSERT(mType == CandidateType::Default || mType == CandidateType::Density,
+ "unhandled candidate type");
+ return Density(-1);
+}
+
+void ResponsiveImageCandidate::AppendDescriptors(
+ nsAString& aDescriptors) const {
+ MOZ_ASSERT(IsValid());
+ switch (mType) {
+ case CandidateType::Default:
+ case CandidateType::Invalid:
+ return;
+ case CandidateType::ComputedFromWidth:
+ aDescriptors.Append(' ');
+ aDescriptors.AppendInt(mValue.mWidth);
+ aDescriptors.Append('w');
+ return;
+ case CandidateType::Density:
+ aDescriptors.Append(' ');
+ aDescriptors.AppendFloat(mValue.mDensity);
+ aDescriptors.Append('x');
+ return;
+ }
+}
+
+double ResponsiveImageCandidate::Density(double aMatchingWidth) const {
+ if (mType == CandidateType::Invalid) {
+ MOZ_ASSERT(false, "Getting density for uninitialized candidate");
+ return 1.0;
+ }
+
+ if (mType == CandidateType::Default) {
+ return 1.0;
+ }
+
+ if (mType == CandidateType::Density) {
+ return mValue.mDensity;
+ }
+ if (mType == CandidateType::ComputedFromWidth) {
+ if (aMatchingWidth < 0) {
+ MOZ_ASSERT(
+ false,
+ "Don't expect to have a negative matching width at this point");
+ return 1.0;
+ }
+ double density = double(mValue.mWidth) / aMatchingWidth;
+ MOZ_ASSERT(density > 0.0);
+ return density;
+ }
+
+ MOZ_ASSERT(false, "Unknown candidate type");
+ return 1.0;
+}
+
+} // namespace mozilla::dom