widget/nsNativeTheme.cpp

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 #include "nsNativeTheme.h"
   7 #include "nsIWidget.h"
   8 #include "mozilla/dom/Document.h"
   9 #include "nsIContent.h"
  10 #include "nsIFrame.h"
  11 #include "nsIScrollableFrame.h"
  12 #include "nsLayoutUtils.h"
  13 #include "nsNumberControlFrame.h"
  14 #include "nsPresContext.h"
  15 #include "nsString.h"
  16 #include "nsNameSpaceManager.h"
  17 #include "nsStyleConsts.h"
  18 #include "nsPIDOMWindow.h"
  19 #include "nsProgressFrame.h"
  20 #include "nsMeterFrame.h"
  21 #include "nsMenuFrame.h"
  22 #include "nsRangeFrame.h"
  23 #include "nsCSSRendering.h"
  24 #include "ImageContainer.h"
  25 #include "mozilla/ComputedStyle.h"
  26 #include "mozilla/EventStates.h"
  27 #include "mozilla/dom/Element.h"
  28 #include "mozilla/dom/HTMLBodyElement.h"
  29 #include "mozilla/dom/HTMLInputElement.h"
  30 #include "mozilla/dom/HTMLProgressElement.h"
  31 #include "mozilla/PresShell.h"
  32 #include "mozilla/StaticPrefs_layout.h"
  33 #include "mozilla/dom/DocumentInlines.h"
  34 #include "mozilla/RelativeLuminanceUtils.h"
  35 #include <algorithm>
  36
  37 using namespace mozilla;
  38 using namespace mozilla::dom;
  39
  40 nsNativeTheme::nsNativeTheme() : mAnimatedContentTimeout(UINT32_MAX) {}
  41
  42 NS_IMPL_ISUPPORTS(nsNativeTheme, nsITimerCallback, nsINamed)
  43
  44 /* static */ EventStates nsNativeTheme::GetContentState(
  45     nsIFrame* aFrame, StyleAppearance aAppearance) {
  46   if (!aFrame) {
  47     return EventStates();
  48   }
  49
  50   nsIContent* frameContent = aFrame->GetContent();
  51   if (!frameContent || !frameContent->IsElement()) {
  52     return EventStates();
  53   }
  54
  55   const bool isXULElement = frameContent->IsXULElement();
  56   if (isXULElement) {
  57     if (aAppearance == StyleAppearance::CheckboxLabel ||
  58         aAppearance == StyleAppearance::RadioLabel) {
  59       aFrame = aFrame->GetParent()->GetParent();
  60       frameContent = aFrame->GetContent();
  61     } else if (aAppearance == StyleAppearance::Checkbox ||
  62                aAppearance == StyleAppearance::Radio ||
  63                aAppearance == StyleAppearance::ToolbarbuttonDropdown ||
  64                aAppearance == StyleAppearance::Treeheadersortarrow ||
  65                aAppearance == StyleAppearance::ButtonArrowPrevious ||
  66                aAppearance == StyleAppearance::ButtonArrowNext ||
  67                aAppearance == StyleAppearance::ButtonArrowUp ||
  68                aAppearance == StyleAppearance::ButtonArrowDown) {
  69       aFrame = aFrame->GetParent();
  70       frameContent = aFrame->GetContent();
  71     }
  72     MOZ_ASSERT(frameContent && frameContent->IsElement());
  73   }
  74
  75   EventStates flags = frameContent->AsElement()->State();
  76   nsNumberControlFrame* numberControlFrame =
  77       nsNumberControlFrame::GetNumberControlFrameForSpinButton(aFrame);
  78   if (numberControlFrame &&
  79       numberControlFrame->GetContent()->AsElement()->State().HasState(
  80           NS_EVENT_STATE_DISABLED)) {
  81     flags |= NS_EVENT_STATE_DISABLED;
  82   }
  83
  84   if (!isXULElement) {
  85     return flags;
  86   }
  87
  88   if (CheckBooleanAttr(aFrame, nsGkAtoms::disabled)) {
  89     flags |= NS_EVENT_STATE_DISABLED;
  90   }
  91
  92   switch (aAppearance) {
  93     case StyleAppearance::RadioLabel:
  94     case StyleAppearance::Radio: {
  95       if (CheckBooleanAttr(aFrame, nsGkAtoms::focused)) {
  96         flags |= NS_EVENT_STATE_FOCUS;
  97         nsPIDOMWindowOuter* window =
  98             aFrame->GetContent()->OwnerDoc()->GetWindow();
  99         if (window && window->ShouldShowFocusRing()) {
 100           flags |= NS_EVENT_STATE_FOCUSRING;
 101         }
 102       }
 103       if (CheckBooleanAttr(aFrame, nsGkAtoms::selected)) {
 104         flags |= NS_EVENT_STATE_CHECKED;
 105       }
 106       break;
 107     }
 108     case StyleAppearance::CheckboxLabel:
 109     case StyleAppearance::Checkbox: {
 110       if (CheckBooleanAttr(aFrame, nsGkAtoms::checked)) {
 111         flags |= NS_EVENT_STATE_CHECKED;
 112       } else if (CheckBooleanAttr(aFrame, nsGkAtoms::indeterminate)) {
 113         flags |= NS_EVENT_STATE_INDETERMINATE;
 114       }
 115       break;
 116     }
 117     case StyleAppearance::MenulistButton:
 118     case StyleAppearance::Menulist:
 119     case StyleAppearance::NumberInput:
 120     case StyleAppearance::Textfield:
 121     case StyleAppearance::Searchfield:
 122     case StyleAppearance::Textarea: {
 123       if (CheckBooleanAttr(aFrame, nsGkAtoms::focused)) {
 124         flags |= NS_EVENT_STATE_FOCUS | NS_EVENT_STATE_FOCUSRING;
 125       }
 126       break;
 127     }
 128     default:
 129       break;
 130   }
 131
 132   return flags;
 133 }
 134
 135 /* static */
 136 bool nsNativeTheme::CheckBooleanAttr(nsIFrame* aFrame, nsAtom* aAtom) {
 137   if (!aFrame) return false;
 138
 139   nsIContent* content = aFrame->GetContent();
 140   if (!content || !content->IsElement()) return false;
 141
 142   if (content->IsHTMLElement())
 143     return content->AsElement()->HasAttr(kNameSpaceID_None, aAtom);
 144
 145   // For XML/XUL elements, an attribute must be equal to the literal
 146   // string "true" to be counted as true.  An empty string should _not_
 147   // be counted as true.
 148   return content->AsElement()->AttrValueIs(kNameSpaceID_None, aAtom, u"true"_ns,
 149                                            eCaseMatters);
 150 }
 151
 152 /* static */
 153 int32_t nsNativeTheme::CheckIntAttr(nsIFrame* aFrame, nsAtom* aAtom,
 154                                     int32_t defaultValue) {
 155   if (!aFrame) return defaultValue;
 156
 157   nsIContent* content = aFrame->GetContent();
 158   if (!content || !content->IsElement()) return defaultValue;
 159
 160   nsAutoString attr;
 161   content->AsElement()->GetAttr(kNameSpaceID_None, aAtom, attr);
 162   nsresult err;
 163   int32_t value = attr.ToInteger(&err);
 164   if (attr.IsEmpty() || NS_FAILED(err)) return defaultValue;
 165
 166   return value;
 167 }
 168
 169 /* static */
 170 double nsNativeTheme::GetProgressValue(nsIFrame* aFrame) {
 171   if (!aFrame || !aFrame->GetContent()->IsHTMLElement(nsGkAtoms::progress)) {
 172     return 0;
 173   }
 174
 175   return static_cast<HTMLProgressElement*>(aFrame->GetContent())->Value();
 176 }
 177
 178 /* static */
 179 double nsNativeTheme::GetProgressMaxValue(nsIFrame* aFrame) {
 180   if (!aFrame || !aFrame->GetContent()->IsHTMLElement(nsGkAtoms::progress)) {
 181     return 100;
 182   }
 183
 184   return static_cast<HTMLProgressElement*>(aFrame->GetContent())->Max();
 185 }
 186
 187 bool nsNativeTheme::IsButtonTypeMenu(nsIFrame* aFrame) {
 188   if (!aFrame) return false;
 189
 190   nsIContent* content = aFrame->GetContent();
 191   return content->IsXULElement(nsGkAtoms::button) &&
 192          content->AsElement()->AttrValueIs(kNameSpaceID_None, nsGkAtoms::type,
 193                                            u"menu"_ns, eCaseMatters);
 194 }
 195
 196 bool nsNativeTheme::IsPressedButton(nsIFrame* aFrame) {
 197   EventStates eventState =
 198       GetContentState(aFrame, StyleAppearance::Toolbarbutton);
 199   if (eventState.HasState(NS_EVENT_STATE_DISABLED)) return false;
 200
 201   return IsOpenButton(aFrame) ||
 202          eventState.HasAllStates(NS_EVENT_STATE_ACTIVE | NS_EVENT_STATE_HOVER);
 203 }
 204
 205 bool nsNativeTheme::IsWidgetStyled(nsPresContext* aPresContext,
 206                                    nsIFrame* aFrame,
 207                                    StyleAppearance aAppearance) {
 208   // Check for specific widgets to see if HTML has overridden the style.
 209   if (!aFrame) {
 210     return false;
 211   }
 212
 213   // Resizers have some special handling, dependent on whether in a scrollable
 214   // container or not. If so, use the scrollable container's to determine
 215   // whether the style is overriden instead of the resizer. This allows a
 216   // non-native transparent resizer to be used instead. Otherwise, we just
 217   // fall through and return false.
 218   if (aAppearance == StyleAppearance::Resizer) {
 219     nsIFrame* parentFrame = aFrame->GetParent();
 220     if (parentFrame && parentFrame->IsScrollFrame()) {
 221       // if the parent is a scrollframe, the resizer should be native themed
 222       // only if the scrollable area doesn't override the widget style.
 223       //
 224       // note that the condition below looks a bit suspect but it's the right
 225       // one. If there's no valid appearance, then we should return true, it's
 226       // effectively the same as if it had overridden the appearance.
 227       parentFrame = parentFrame->GetParent();
 228       if (!parentFrame) {
 229         return false;
 230       }
 231       auto parentAppearance =
 232           parentFrame->StyleDisplay()->EffectiveAppearance();
 233       return parentAppearance == StyleAppearance::None ||
 234              IsWidgetStyled(aPresContext, parentFrame, parentAppearance);
 235     }
 236   }
 237
 238   /**
 239    * Progress bar appearance should be the same for the bar and the container
 240    * frame. nsProgressFrame owns the logic and will tell us what we should do.
 241    */
 242   if (aAppearance == StyleAppearance::Progresschunk ||
 243       aAppearance == StyleAppearance::ProgressBar) {
 244     nsProgressFrame* progressFrame = do_QueryFrame(
 245         aAppearance == StyleAppearance::Progresschunk ? aFrame->GetParent()
 246                                                       : aFrame);
 247     if (progressFrame) {
 248       return !progressFrame->ShouldUseNativeStyle();
 249     }
 250   }
 251
 252   /**
 253    * Meter bar appearance should be the same for the bar and the container
 254    * frame. nsMeterFrame owns the logic and will tell us what we should do.
 255    */
 256   if (aAppearance == StyleAppearance::Meterchunk ||
 257       aAppearance == StyleAppearance::Meter) {
 258     nsMeterFrame* meterFrame = do_QueryFrame(
 259         aAppearance == StyleAppearance::Meterchunk ? aFrame->GetParent()
 260                                                    : aFrame);
 261     if (meterFrame) {
 262       return !meterFrame->ShouldUseNativeStyle();
 263     }
 264   }
 265
 266   /**
 267    * An nsRangeFrame and its children are treated atomically when it
 268    * comes to native theming (either all parts, or no parts, are themed).
 269    * nsRangeFrame owns the logic and will tell us what we should do.
 270    */
 271   if (aAppearance == StyleAppearance::Range ||
 272       aAppearance == StyleAppearance::RangeThumb) {
 273     nsRangeFrame* rangeFrame = do_QueryFrame(
 274         aAppearance == StyleAppearance::RangeThumb ? aFrame->GetParent()
 275                                                    : aFrame);
 276     if (rangeFrame) {
 277       return !rangeFrame->ShouldUseNativeStyle();
 278     }
 279   }
 280
 281   return nsLayoutUtils::AuthorSpecifiedBorderBackgroundDisablesTheming(
 282              aAppearance) &&
 283          aFrame->GetContent()->IsHTMLElement() &&
 284          aFrame->Style()->HasAuthorSpecifiedBorderOrBackground();
 285 }
 286
 287 /* static */
 288 bool nsNativeTheme::IsFrameRTL(nsIFrame* aFrame) {
 289   if (!aFrame) {
 290     return false;
 291   }
 292   return aFrame->GetWritingMode().IsPhysicalRTL();
 293 }
 294
 295 /* static */
 296 bool nsNativeTheme::IsHTMLContent(nsIFrame* aFrame) {
 297   if (!aFrame) {
 298     return false;
 299   }
 300   nsIContent* content = aFrame->GetContent();
 301   return content && content->IsHTMLElement();
 302 }
 303
 304 // treeheadercell:
 305 nsNativeTheme::TreeSortDirection nsNativeTheme::GetTreeSortDirection(
 306     nsIFrame* aFrame) {
 307   if (!aFrame || !aFrame->GetContent()) return eTreeSortDirection_Natural;
 308
 309   static Element::AttrValuesArray strings[] = {nsGkAtoms::descending,
 310                                                nsGkAtoms::ascending, nullptr};
 311
 312   nsIContent* content = aFrame->GetContent();
 313   if (content->IsElement()) {
 314     switch (content->AsElement()->FindAttrValueIn(
 315         kNameSpaceID_None, nsGkAtoms::sortDirection, strings, eCaseMatters)) {
 316       case 0:
 317         return eTreeSortDirection_Descending;
 318       case 1:
 319         return eTreeSortDirection_Ascending;
 320     }
 321   }
 322
 323   return eTreeSortDirection_Natural;
 324 }
 325
 326 bool nsNativeTheme::IsLastTreeHeaderCell(nsIFrame* aFrame) {
 327   if (!aFrame) return false;
 328
 329   // A tree column picker is always the last header cell.
 330   if (aFrame->GetContent()->IsXULElement(nsGkAtoms::treecolpicker)) return true;
 331
 332   // Find the parent tree.
 333   nsIContent* parent = aFrame->GetContent()->GetParent();
 334   while (parent && !parent->IsXULElement(nsGkAtoms::tree)) {
 335     parent = parent->GetParent();
 336   }
 337
 338   // If the column picker is visible, this can't be the last column.
 339   if (parent && !parent->AsElement()->AttrValueIs(kNameSpaceID_None,
 340                                                   nsGkAtoms::hidecolumnpicker,
 341                                                   u"true"_ns, eCaseMatters))
 342     return false;
 343
 344   while ((aFrame = aFrame->GetNextSibling())) {
 345     if (aFrame->GetRect().Width() > 0) return false;
 346   }
 347   return true;
 348 }
 349
 350 // tab:
 351 bool nsNativeTheme::IsBottomTab(nsIFrame* aFrame) {
 352   if (!aFrame) return false;
 353
 354   nsAutoString classStr;
 355   if (aFrame->GetContent()->IsElement()) {
 356     aFrame->GetContent()->AsElement()->GetAttr(kNameSpaceID_None,
 357                                                nsGkAtoms::_class, classStr);
 358   }
 359   // FIXME: This looks bogus, shouldn't this be looking at GetClasses()?
 360   return !classStr.IsEmpty() && classStr.Find("tab-bottom") != kNotFound;
 361 }
 362
 363 bool nsNativeTheme::IsFirstTab(nsIFrame* aFrame) {
 364   if (!aFrame) return false;
 365
 366   for (nsIFrame* first : aFrame->GetParent()->PrincipalChildList()) {
 367     if (first->GetRect().Width() > 0 &&
 368         first->GetContent()->IsXULElement(nsGkAtoms::tab))
 369       return (first == aFrame);
 370   }
 371   return false;
 372 }
 373
 374 bool nsNativeTheme::IsHorizontal(nsIFrame* aFrame) {
 375   if (!aFrame) return false;
 376
 377   if (!aFrame->GetContent()->IsElement()) return true;
 378
 379   return !aFrame->GetContent()->AsElement()->AttrValueIs(
 380       kNameSpaceID_None, nsGkAtoms::orient, nsGkAtoms::vertical, eCaseMatters);
 381 }
 382
 383 bool nsNativeTheme::IsNextToSelectedTab(nsIFrame* aFrame, int32_t aOffset) {
 384   if (!aFrame) return false;
 385
 386   if (aOffset == 0) return IsSelectedTab(aFrame);
 387
 388   int32_t thisTabIndex = -1, selectedTabIndex = -1;
 389
 390   nsIFrame* currentTab = aFrame->GetParent()->PrincipalChildList().FirstChild();
 391   for (int32_t i = 0; currentTab; currentTab = currentTab->GetNextSibling()) {
 392     if (currentTab->GetRect().Width() == 0) continue;
 393     if (aFrame == currentTab) thisTabIndex = i;
 394     if (IsSelectedTab(currentTab)) selectedTabIndex = i;
 395     ++i;
 396   }
 397
 398   if (thisTabIndex == -1 || selectedTabIndex == -1) return false;
 399
 400   return (thisTabIndex - selectedTabIndex == aOffset);
 401 }
 402
 403 bool nsNativeTheme::IsVerticalProgress(nsIFrame* aFrame) {
 404   if (!aFrame) {
 405     return false;
 406   }
 407   return IsVerticalMeter(aFrame);
 408 }
 409
 410 bool nsNativeTheme::IsVerticalMeter(nsIFrame* aFrame) {
 411   MOZ_ASSERT(aFrame, "You have to pass a non-null aFrame");
 412   switch (aFrame->StyleDisplay()->mOrient) {
 413     case StyleOrient::Horizontal:
 414       return false;
 415     case StyleOrient::Vertical:
 416       return true;
 417     case StyleOrient::Inline:
 418       return aFrame->GetWritingMode().IsVertical();
 419     case StyleOrient::Block:
 420       return !aFrame->GetWritingMode().IsVertical();
 421   }
 422   MOZ_ASSERT_UNREACHABLE("unexpected -moz-orient value");
 423   return false;
 424 }
 425
 426 // menupopup:
 427 bool nsNativeTheme::IsSubmenu(nsIFrame* aFrame, bool* aLeftOfParent) {
 428   if (!aFrame) return false;
 429
 430   nsIContent* parentContent = aFrame->GetContent()->GetParent();
 431   if (!parentContent || !parentContent->IsXULElement(nsGkAtoms::menu))
 432     return false;
 433
 434   nsIFrame* parent = aFrame;
 435   while ((parent = parent->GetParent())) {
 436     if (parent->GetContent() == parentContent) {
 437       if (aLeftOfParent) {
 438         LayoutDeviceIntRect selfBounds, parentBounds;
 439         selfBounds = aFrame->GetNearestWidget()->GetScreenBounds();
 440         parentBounds = parent->GetNearestWidget()->GetScreenBounds();
 441         *aLeftOfParent = selfBounds.X() < parentBounds.X();
 442       }
 443       return true;
 444     }
 445   }
 446
 447   return false;
 448 }
 449
 450 bool nsNativeTheme::QueueAnimatedContentForRefresh(nsIContent* aContent,
 451                                                    uint32_t aMinimumFrameRate) {
 452   NS_ASSERTION(aContent, "Null pointer!");
 453   NS_ASSERTION(aMinimumFrameRate, "aMinimumFrameRate must be non-zero!");
 454   NS_ASSERTION(aMinimumFrameRate <= 1000,
 455                "aMinimumFrameRate must be less than 1000!");
 456
 457   uint32_t timeout = 1000 / aMinimumFrameRate;
 458   timeout = std::min(mAnimatedContentTimeout, timeout);
 459
 460   if (!mAnimatedContentTimer) {
 461     mAnimatedContentTimer = NS_NewTimer();
 462     NS_ENSURE_TRUE(mAnimatedContentTimer, false);
 463   }
 464
 465   if (mAnimatedContentList.IsEmpty() || timeout != mAnimatedContentTimeout) {
 466     nsresult rv;
 467     if (!mAnimatedContentList.IsEmpty()) {
 468       rv = mAnimatedContentTimer->Cancel();
 469       NS_ENSURE_SUCCESS(rv, false);
 470     }
 471
 472     if (XRE_IsContentProcess() && NS_IsMainThread()) {
 473       mAnimatedContentTimer->SetTarget(
 474           aContent->OwnerDoc()->EventTargetFor(TaskCategory::Other));
 475     }
 476     rv = mAnimatedContentTimer->InitWithCallback(this, timeout,
 477                                                  nsITimer::TYPE_ONE_SHOT);
 478     NS_ENSURE_SUCCESS(rv, false);
 479
 480     mAnimatedContentTimeout = timeout;
 481   }
 482
 483   // XXX(Bug 1631371) Check if this should use a fallible operation as it
 484   // pretended earlier.
 485   mAnimatedContentList.AppendElement(aContent);
 486
 487   return true;
 488 }
 489
 490 NS_IMETHODIMP
 491 nsNativeTheme::Notify(nsITimer* aTimer) {
 492   NS_ASSERTION(aTimer == mAnimatedContentTimer, "Wrong timer!");
 493
 494   // XXX Assumes that calling nsIFrame::Invalidate won't reenter
 495   //     QueueAnimatedContentForRefresh.
 496
 497   uint32_t count = mAnimatedContentList.Length();
 498   for (uint32_t index = 0; index < count; index++) {
 499     nsIFrame* frame = mAnimatedContentList[index]->GetPrimaryFrame();
 500     if (frame) {
 501       frame->InvalidateFrame();
 502     }
 503   }
 504
 505   mAnimatedContentList.Clear();
 506   mAnimatedContentTimeout = UINT32_MAX;
 507   return NS_OK;
 508 }
 509
 510 NS_IMETHODIMP
 511 nsNativeTheme::GetName(nsACString& aName) {
 512   aName.AssignLiteral("nsNativeTheme");
 513   return NS_OK;
 514 }
 515
 516 nsIFrame* nsNativeTheme::GetAdjacentSiblingFrameWithSameAppearance(
 517     nsIFrame* aFrame, bool aNextSibling) {
 518   if (!aFrame) return nullptr;
 519
 520   // Find the next visible sibling.
 521   nsIFrame* sibling = aFrame;
 522   do {
 523     sibling =
 524         aNextSibling ? sibling->GetNextSibling() : sibling->GetPrevSibling();
 525   } while (sibling && sibling->GetRect().Width() == 0);
 526
 527   // Check same appearance and adjacency.
 528   if (!sibling ||
 529       sibling->StyleDisplay()->EffectiveAppearance() !=
 530           aFrame->StyleDisplay()->EffectiveAppearance() ||
 531       (sibling->GetRect().XMost() != aFrame->GetRect().X() &&
 532        aFrame->GetRect().XMost() != sibling->GetRect().X()))
 533     return nullptr;
 534   return sibling;
 535 }
 536
 537 bool nsNativeTheme::IsRangeHorizontal(nsIFrame* aFrame) {
 538   nsIFrame* rangeFrame = aFrame;
 539   if (!rangeFrame->IsRangeFrame()) {
 540     // If the thumb's frame is passed in, get its range parent:
 541     rangeFrame = aFrame->GetParent();
 542   }
 543   if (rangeFrame->IsRangeFrame()) {
 544     return static_cast<nsRangeFrame*>(rangeFrame)->IsHorizontal();
 545   }
 546   // Not actually a range frame - just use the ratio of the frame's size to
 547   // decide:
 548   return aFrame->GetSize().width >= aFrame->GetSize().height;
 549 }
 550
 551 static nsIFrame* GetBodyFrame(nsIFrame* aCanvasFrame) {
 552   nsIContent* body = aCanvasFrame->PresContext()->Document()->GetBodyElement();
 553   if (!body) {
 554     return nullptr;
 555   }
 556   return body->GetPrimaryFrame();
 557 }
 558
 559 bool nsNativeTheme::IsDarkColor(nscolor aColor) {
 560   // Given https://www.w3.org/TR/WCAG20/#contrast-ratiodef, this is the
 561   // threshold that tells us whether contrast is better against white or black.
 562   //
 563   // Contrast ratio against black is: (L + 0.05) / 0.05
 564   // Contrast ratio against white is: 1.05 / (L + 0.05)
 565   //
 566   // So the intersection is:
 567   //
 568   //   (L + 0.05) / 0.05 = 1.05 / (L + 0.05)
 569   //
 570   // And the solution to that equation is:
 571   //
 572   //   sqrt(1.05 * 0.05) - 0.05
 573   //
 574   // So we consider a color dark if the contrast is below this threshold, and
 575   // it's at least half-opaque.
 576   constexpr float kThreshold = 0.179129;
 577   return NS_GET_A(aColor) > 127 &&
 578          RelativeLuminanceUtils::Compute(aColor) < kThreshold;
 579 }
 580
 581 /* static */
 582 bool nsNativeTheme::IsDarkBackground(nsIFrame* aFrame) {
 583   // Try to find the scrolled frame. Note that for stuff like xul <tree> there
 584   // might be none.
 585   {
 586     nsIFrame* frame = aFrame;
 587     nsIScrollableFrame* scrollFrame = nullptr;
 588     while (!scrollFrame && frame) {
 589       scrollFrame = frame->GetScrollTargetFrame();
 590       frame = frame->GetParent();
 591     }
 592     if (scrollFrame) {
 593       aFrame = scrollFrame->GetScrolledFrame();
 594     } else {
 595       // Leave aFrame untouched.
 596     }
 597   }
 598
 599   auto backgroundFrame = nsCSSRendering::FindNonTransparentBackgroundFrame(
 600       aFrame, /* aStopAtThemed = */ false);
 601   if (!backgroundFrame.mFrame) {
 602     return false;
 603   }
 604
 605   nscolor color = backgroundFrame.mFrame->StyleBackground()->BackgroundColor(
 606       backgroundFrame.mFrame);
 607
 608   if (backgroundFrame.mIsForCanvas) {
 609     // For canvas frames, prefer to look at the body first, because the body
 610     // background color is most likely what will be visible as the background
 611     // color of the page, even if the html element has a different background
 612     // color which prevents that of the body frame to propagate to the viewport.
 613     if (nsIFrame* bodyFrame = GetBodyFrame(aFrame)) {
 614       nscolor bodyColor =
 615           bodyFrame->StyleBackground()->BackgroundColor(bodyFrame);
 616       if (NS_GET_A(bodyColor)) {
 617         color = bodyColor;
 618       }
 619     }
 620   }
 621
 622   return IsDarkColor(color);
 623 }
 624
 625 /*static*/
 626 bool nsNativeTheme::IsWidgetScrollbarPart(StyleAppearance aAppearance) {
 627   switch (aAppearance) {
 628     case StyleAppearance::ScrollbarVertical:
 629     case StyleAppearance::ScrollbarHorizontal:
 630     case StyleAppearance::ScrollbarbuttonUp:
 631     case StyleAppearance::ScrollbarbuttonDown:
 632     case StyleAppearance::ScrollbarbuttonLeft:
 633     case StyleAppearance::ScrollbarbuttonRight:
 634     case StyleAppearance::ScrollbarthumbVertical:
 635     case StyleAppearance::ScrollbarthumbHorizontal:
 636     case StyleAppearance::ScrollbartrackHorizontal:
 637     case StyleAppearance::ScrollbartrackVertical:
 638     case StyleAppearance::Scrollcorner:
 639       return true;
 640     default:
 641       return false;
 642   }
 643 }