gecko-dev/widget/windows/nsWindowGfx.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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/. */

/*
 * nsWindowGfx - Painting and aceleration.
 */

/**************************************************************
 **************************************************************
 **
 ** BLOCK: Includes
 **
 ** Include headers.
 **
 **************************************************************
 **************************************************************/

#include "mozilla/dom/ContentParent.h"

#include "nsWindowGfx.h"
#include "nsAppRunner.h"
#include <windows.h>
#include <shellapi.h>
#include "gfxEnv.h"
#include "gfxImageSurface.h"
#include "gfxUtils.h"
#include "gfxConfig.h"
#include "gfxWindowsSurface.h"
#include "gfxWindowsPlatform.h"
#include "gfxDWriteFonts.h"
#include "mozilla/gfx/2D.h"
#include "mozilla/gfx/DataSurfaceHelpers.h"
#include "mozilla/gfx/Tools.h"
#include "mozilla/RefPtr.h"
#include "mozilla/UniquePtrExtensions.h"
#include "nsGfxCIID.h"
#include "gfxContext.h"
#include "WinUtils.h"
#include "WinWindowOcclusionTracker.h"
#include "nsIWidgetListener.h"
#include "mozilla/Unused.h"
#include "nsDebug.h"
#include "WindowRenderer.h"
#include "mozilla/layers/WebRenderLayerManager.h"

#include "mozilla/gfx/GPUProcessManager.h"
#include "mozilla/layers/CompositorBridgeParent.h"
#include "mozilla/layers/CompositorBridgeChild.h"
#include "InProcessWinCompositorWidget.h"

#include "nsUXThemeData.h"
#include "nsUXThemeConstants.h"

using namespace mozilla;
using namespace mozilla::gfx;
using namespace mozilla::layers;
using namespace mozilla::widget;
using namespace mozilla::plugins;
extern mozilla::LazyLogModule gWindowsLog;

/**************************************************************
 **************************************************************
 **
 ** BLOCK: Variables
 **
 ** nsWindow Class static initializations and global variables.
 **
 **************************************************************
 **************************************************************/

/**************************************************************
 *
 * SECTION: nsWindow statics
 *
 **************************************************************/

struct IconMetrics {
  int32_t xMetric;
  int32_t yMetric;
  int32_t defaultSize;
};

// Corresponds 1:1 to the IconSizeType enum
static IconMetrics sIconMetrics[] = {
    {SM_CXSMICON, SM_CYSMICON, 16},  // small icon
    {SM_CXICON, SM_CYICON, 32}       // regular icon
};

/**************************************************************
 **************************************************************
 **
 ** BLOCK: nsWindow impl.
 **
 ** Paint related nsWindow methods.
 **
 **************************************************************
 **************************************************************/

// GetRegionToPaint returns the invalidated region that needs to be painted
LayoutDeviceIntRegion nsWindow::GetRegionToPaint(bool aForceFullRepaint,
                                                 PAINTSTRUCT ps, HDC aDC) {
  if (aForceFullRepaint) {
    RECT paintRect;
    ::GetClientRect(mWnd, &paintRect);
    return LayoutDeviceIntRegion(WinUtils::ToIntRect(paintRect));
  }

  HRGN paintRgn = ::CreateRectRgn(0, 0, 0, 0);
  if (paintRgn != nullptr) {
    int result = GetRandomRgn(aDC, paintRgn, SYSRGN);
    if (result == 1) {
      POINT pt = {0, 0};
      ::MapWindowPoints(nullptr, mWnd, &pt, 1);
      ::OffsetRgn(paintRgn, pt.x, pt.y);
    }
    LayoutDeviceIntRegion rgn(WinUtils::ConvertHRGNToRegion(paintRgn));
    ::DeleteObject(paintRgn);
    return rgn;
  }
  return LayoutDeviceIntRegion(WinUtils::ToIntRect(ps.rcPaint));
}

nsIWidgetListener* nsWindow::GetPaintListener() {
  if (mDestroyCalled) return nullptr;
  return mAttachedWidgetListener ? mAttachedWidgetListener : mWidgetListener;
}

void nsWindow::ForcePresent() {
  if (mResizeState != RESIZING) {
    if (CompositorBridgeChild* remoteRenderer = GetRemoteRenderer()) {
      remoteRenderer->SendForcePresent(wr::RenderReasons::WIDGET);
    }
  }
}

bool nsWindow::OnPaint(uint32_t aNestingLevel) {
  gfx::DeviceResetReason resetReason = gfx::DeviceResetReason::OK;
  if (gfxWindowsPlatform::GetPlatform()->DidRenderingDeviceReset(
          &resetReason)) {
    gfxCriticalNote << "(nsWindow) Detected device reset: " << (int)resetReason;

    gfxWindowsPlatform::GetPlatform()->UpdateRenderMode();

    GPUProcessManager::GPUProcessManager::NotifyDeviceReset(
        resetReason, gfx::DeviceResetDetectPlace::WIDGET);

    gfxCriticalNote << "(nsWindow) Finished device reset.";
    return false;
  }

  PAINTSTRUCT ps;

  // Avoid starting the GPU process for the initial navigator:blank window.
  if (mIsEarlyBlankWindow) {
    // Call BeginPaint/EndPaint or Windows will keep sending us messages.
    ::BeginPaint(mWnd, &ps);
    ::EndPaint(mWnd, &ps);
    return true;
  }

  WindowRenderer* renderer = GetWindowRenderer();
  KnowsCompositor* knowsCompositor = renderer->AsKnowsCompositor();
  WebRenderLayerManager* layerManager = renderer->AsWebRender();

  if (mClearNCEdge) {
    // We need to clear this edge of the non-client region to black (once).
    HDC hdc;
    RECT rect;
    hdc = ::GetWindowDC(mWnd);
    ::GetWindowRect(mWnd, &rect);
    ::MapWindowPoints(nullptr, mWnd, (LPPOINT)&rect, 2);
    switch (mClearNCEdge.value()) {
      case ABE_TOP:
        rect.bottom = rect.top + kHiddenTaskbarSize;
        break;
      case ABE_LEFT:
        rect.right = rect.left + kHiddenTaskbarSize;
        break;
      case ABE_BOTTOM:
        rect.top = rect.bottom - kHiddenTaskbarSize;
        break;
      case ABE_RIGHT:
        rect.left = rect.right - kHiddenTaskbarSize;
        break;
      default:
        MOZ_ASSERT_UNREACHABLE("Invalid edge value");
        break;
    }
    ::FillRect(hdc, &rect,
               reinterpret_cast<HBRUSH>(::GetStockObject(BLACK_BRUSH)));
    ::ReleaseDC(mWnd, hdc);

    mClearNCEdge.reset();
  }

  if (knowsCompositor && layerManager &&
      !mBounds.IsEqualEdges(mLastPaintBounds)) {
    // Do an early async composite so that we at least have something on the
    // screen in the right place, even if the content is out of date.
    layerManager->ScheduleComposite(wr::RenderReasons::WIDGET);
  }
  mLastPaintBounds = mBounds;

  // For layered translucent windows all drawing should go to memory DC and no
  // WM_PAINT messages are normally generated. To support asynchronous painting
  // we force generation of WM_PAINT messages by invalidating window areas with
  // RedrawWindow, InvalidateRect or InvalidateRgn function calls.
  const bool usingMemoryDC =
      renderer->GetBackendType() == LayersBackend::LAYERS_NONE &&
      mTransparencyMode == TransparencyMode::Transparent;

  HDC hDC = nullptr;
  if (usingMemoryDC) {
    // BeginPaint/EndPaint must be called to make Windows think that invalid
    // area is painted. Otherwise it will continue sending the same message
    // endlessly.
    ::BeginPaint(mWnd, &ps);
    ::EndPaint(mWnd, &ps);

    // We're guaranteed to have a widget proxy since we called
    // GetLayerManager().
    hDC = mBasicLayersSurface->GetTransparentDC();
  } else {
    hDC = ::BeginPaint(mWnd, &ps);
  }

  const bool forceRepaint = mTransparencyMode == TransparencyMode::Transparent;
  const LayoutDeviceIntRegion region = GetRegionToPaint(forceRepaint, ps, hDC);

  if (knowsCompositor && layerManager) {
    // We need to paint to the screen even if nothing changed, since if we
    // don't have a compositing window manager, our pixels could be stale.
    layerManager->SetNeedsComposite(true);
    layerManager->SendInvalidRegion(region.ToUnknownRegion());
  }

  RefPtr<nsWindow> strongThis(this);

  nsIWidgetListener* listener = GetPaintListener();
  if (listener) {
    listener->WillPaintWindow(this);
  }
  // Re-get the listener since the will paint notification may have killed it.
  listener = GetPaintListener();
  if (!listener) {
    return false;
  }

  if (knowsCompositor && layerManager && layerManager->NeedsComposite()) {
    layerManager->ScheduleComposite(wr::RenderReasons::WIDGET);
    layerManager->SetNeedsComposite(false);
  }

  bool result = true;
  if (!region.IsEmpty() && listener) {
    // Should probably pass in a real region here, using GetRandomRgn
    // http://msdn.microsoft.com/library/default.asp?url=/library/en-us/gdi/clipping_4q0e.asp

#ifdef WIDGET_DEBUG_OUTPUT
    debug_DumpPaintEvent(stdout, this, region.ToUnknownRegion(), "noname",
                         (int32_t)mWnd);
#endif  // WIDGET_DEBUG_OUTPUT

    switch (renderer->GetBackendType()) {
      case LayersBackend::LAYERS_NONE: {
        RefPtr<gfxASurface> targetSurface;

        // don't support transparency for non-GDI rendering, for now
        if (TransparencyMode::Transparent == mTransparencyMode) {
          // This mutex needs to be held when EnsureTransparentSurface is
          // called.
          MutexAutoLock lock(mBasicLayersSurface->GetTransparentSurfaceLock());
          targetSurface = mBasicLayersSurface->EnsureTransparentSurface();
        }

        RefPtr<gfxWindowsSurface> targetSurfaceWin;
        if (!targetSurface) {
          uint32_t flags = (mTransparencyMode == TransparencyMode::Opaque)
                               ? 0
                               : gfxWindowsSurface::FLAG_IS_TRANSPARENT;
          targetSurfaceWin = new gfxWindowsSurface(hDC, flags);
          targetSurface = targetSurfaceWin;
        }

        if (!targetSurface) {
          NS_ERROR("Invalid RenderMode!");
          return false;
        }

        RECT paintRect;
        ::GetClientRect(mWnd, &paintRect);
        RefPtr<DrawTarget> dt = gfxPlatform::CreateDrawTargetForSurface(
            targetSurface, IntSize(paintRect.right - paintRect.left,
                                   paintRect.bottom - paintRect.top));
        if (!dt || !dt->IsValid()) {
          gfxWarning()
              << "nsWindow::OnPaint failed in CreateDrawTargetForSurface";
          return false;
        }

        // don't need to double buffer with anything but GDI
        BufferMode doubleBuffering = mozilla::layers::BufferMode::BUFFER_NONE;
        switch (mTransparencyMode) {
          case TransparencyMode::Transparent:
            // If we're rendering with translucency, we're going to be
            // rendering the whole window; make sure we clear it first
            dt->ClearRect(
                Rect(0.f, 0.f, dt->GetSize().width, dt->GetSize().height));
            break;
          default:
            // If we're not doing translucency, then double buffer
            doubleBuffering = mozilla::layers::BufferMode::BUFFERED;
            break;
        }

        gfxContext thebesContext(dt);

        {
          AutoLayerManagerSetup setupLayerManager(this, &thebesContext,
                                                  doubleBuffering);
          result = listener->PaintWindow(this, region);
        }

        if (TransparencyMode::Transparent == mTransparencyMode) {
          // Data from offscreen drawing surface was copied to memory bitmap of
          // transparent bitmap. Now it can be read from memory bitmap to apply
          // alpha channel and after that displayed on the screen.
          mBasicLayersSurface->RedrawTransparentWindow();
        }
      } break;
      case LayersBackend::LAYERS_WR: {
        result = listener->PaintWindow(this, region);
        if (!gfxEnv::MOZ_DISABLE_FORCE_PRESENT()) {
          nsCOMPtr<nsIRunnable> event = NewRunnableMethod(
              "nsWindow::ForcePresent", this, &nsWindow::ForcePresent);
          NS_DispatchToMainThread(event);
        }
      } break;
      default:
        NS_ERROR("Unknown layers backend used!");
        break;
    }
  }

  if (!usingMemoryDC) {
    ::EndPaint(mWnd, &ps);
  }

  mLastPaintEndTime = TimeStamp::Now();

  // Re-get the listener since painting may have killed it.
  listener = GetPaintListener();
  if (listener) listener->DidPaintWindow();

  if (aNestingLevel == 0 && ::GetUpdateRect(mWnd, nullptr, false)) {
    OnPaint(1);
  }

  return result;
}

bool nsWindow::NeedsToTrackWindowOcclusionState() {
  if (!WinWindowOcclusionTracker::Get()) {
    return false;
  }

  if (mCompositorSession && mWindowType == WindowType::TopLevel) {
    return true;
  }

  return false;
}

void nsWindow::NotifyOcclusionState(mozilla::widget::OcclusionState aState) {
  MOZ_ASSERT(NeedsToTrackWindowOcclusionState());

  bool isFullyOccluded = aState == mozilla::widget::OcclusionState::OCCLUDED;
  // When window is minimized, it is not set as fully occluded.
  if (mFrameState->GetSizeMode() == nsSizeMode_Minimized) {
    isFullyOccluded = false;
  }

  // Don't dispatch if the new occlustion state is the same as the current
  // state.
  if (mIsFullyOccluded == isFullyOccluded) {
    return;
  }

  mIsFullyOccluded = isFullyOccluded;

  MOZ_LOG(gWindowsLog, LogLevel::Info,
          ("nsWindow::NotifyOcclusionState() mIsFullyOccluded %d "
           "mFrameState->GetSizeMode() %d",
           mIsFullyOccluded, mFrameState->GetSizeMode()));

  wr::DebugFlags flags{0};
  flags._0 = gfx::gfxVars::WebRenderDebugFlags();
  bool debugEnabled = bool(flags & wr::DebugFlags::WINDOW_VISIBILITY_DBG);
  if (debugEnabled && mCompositorWidgetDelegate) {
    mCompositorWidgetDelegate->NotifyVisibilityUpdated(
        mFrameState->GetSizeMode(), mIsFullyOccluded);
  }

  if (mWidgetListener) {
    mWidgetListener->OcclusionStateChanged(mIsFullyOccluded);
  }
}

void nsWindow::MaybeEnableWindowOcclusion(bool aEnable) {
  // WindowOcclusion is enabled/disabled only when compositor session exists.
  // See nsWindow::NeedsToTrackWindowOcclusionState().
  if (!mCompositorSession) {
    return;
  }

  bool enabled = gfxConfig::IsEnabled(gfx::Feature::WINDOW_OCCLUSION);

  if (aEnable) {
    // Enable window occlusion.
    if (enabled && NeedsToTrackWindowOcclusionState()) {
      WinWindowOcclusionTracker::Get()->Enable(this, mWnd);

      wr::DebugFlags flags{0};
      flags._0 = gfx::gfxVars::WebRenderDebugFlags();
      bool debugEnabled = bool(flags & wr::DebugFlags::WINDOW_VISIBILITY_DBG);
      if (debugEnabled && mCompositorWidgetDelegate) {
        mCompositorWidgetDelegate->NotifyVisibilityUpdated(
            mFrameState->GetSizeMode(), mIsFullyOccluded);
      }
    }
    return;
  }

  // Disable window occlusion.
  MOZ_ASSERT(!aEnable);

  if (!NeedsToTrackWindowOcclusionState()) {
    return;
  }

  WinWindowOcclusionTracker::Get()->Disable(this, mWnd);
  NotifyOcclusionState(OcclusionState::VISIBLE);

  wr::DebugFlags flags{0};
  flags._0 = gfx::gfxVars::WebRenderDebugFlags();
  bool debugEnabled = bool(flags & wr::DebugFlags::WINDOW_VISIBILITY_DBG);
  if (debugEnabled && mCompositorWidgetDelegate) {
    mCompositorWidgetDelegate->NotifyVisibilityUpdated(
        mFrameState->GetSizeMode(), mIsFullyOccluded);
  }
}

// This override of CreateCompositor is to add support for sending the IPC
// call for RequesetFxrOutput as soon as the compositor for this widget is
// available.
void nsWindow::CreateCompositor() {
  nsBaseWidget::CreateCompositor();

  MaybeEnableWindowOcclusion(/* aEnable */ true);

  if (mRequestFxrOutputPending) {
    GetRemoteRenderer()->SendRequestFxrOutput();
  }
}

void nsWindow::DestroyCompositor() {
  MaybeEnableWindowOcclusion(/* aEnable */ false);

  nsBaseWidget::DestroyCompositor();
}

void nsWindow::RequestFxrOutput() {
  if (GetRemoteRenderer() != nullptr) {
    MOZ_CRASH("RequestFxrOutput should happen before Compositor is created.");
  } else {
    // The compositor isn't ready, so indicate to make the IPC call when
    // it is available.
    mRequestFxrOutputPending = true;
  }
}

LayoutDeviceIntSize nsWindowGfx::GetIconMetrics(IconSizeType aSizeType) {
  int32_t width = ::GetSystemMetrics(sIconMetrics[aSizeType].xMetric);
  int32_t height = ::GetSystemMetrics(sIconMetrics[aSizeType].yMetric);

  if (width == 0 || height == 0) {
    width = height = sIconMetrics[aSizeType].defaultSize;
  }

  return LayoutDeviceIntSize(width, height);
}

nsresult nsWindowGfx::CreateIcon(imgIContainer* aContainer, bool aIsCursor,
                                 LayoutDeviceIntPoint aHotspot,
                                 LayoutDeviceIntSize aScaledSize,
                                 HICON* aIcon) {
  MOZ_ASSERT(aHotspot.x >= 0 && aHotspot.y >= 0);
  MOZ_ASSERT((aScaledSize.width > 0 && aScaledSize.height > 0) ||
             (aScaledSize.width == 0 && aScaledSize.height == 0));

  // Get the image data
  RefPtr<SourceSurface> surface = aContainer->GetFrame(
      imgIContainer::FRAME_CURRENT,
      imgIContainer::FLAG_SYNC_DECODE | imgIContainer::FLAG_ASYNC_NOTIFY);
  NS_ENSURE_TRUE(surface, NS_ERROR_NOT_AVAILABLE);

  IntSize frameSize = surface->GetSize();
  if (frameSize.IsEmpty()) {
    return NS_ERROR_FAILURE;
  }

  IntSize iconSize(aScaledSize.width, aScaledSize.height);
  if (iconSize == IntSize(0, 0)) {  // use frame's intrinsic size
    iconSize = frameSize;
  }

  RefPtr<DataSourceSurface> dataSurface;
  bool mappedOK;
  DataSourceSurface::MappedSurface map;

  if (iconSize != frameSize) {
    // Scale the surface
    dataSurface =
        Factory::CreateDataSourceSurface(iconSize, SurfaceFormat::B8G8R8A8);
    NS_ENSURE_TRUE(dataSurface, NS_ERROR_FAILURE);
    mappedOK = dataSurface->Map(DataSourceSurface::MapType::READ_WRITE, &map);
    NS_ENSURE_TRUE(mappedOK, NS_ERROR_FAILURE);

    RefPtr<DrawTarget> dt = Factory::CreateDrawTargetForData(
        BackendType::CAIRO, map.mData, dataSurface->GetSize(), map.mStride,
        SurfaceFormat::B8G8R8A8);
    if (!dt) {
      gfxWarning()
          << "nsWindowGfx::CreatesIcon failed in CreateDrawTargetForData";
      return NS_ERROR_OUT_OF_MEMORY;
    }
    dt->DrawSurface(surface, Rect(0, 0, iconSize.width, iconSize.height),
                    Rect(0, 0, frameSize.width, frameSize.height),
                    DrawSurfaceOptions(),
                    DrawOptions(1.0f, CompositionOp::OP_SOURCE));
  } else if (surface->GetFormat() != SurfaceFormat::B8G8R8A8) {
    // Convert format to SurfaceFormat::B8G8R8A8
    dataSurface = gfxUtils::CopySurfaceToDataSourceSurfaceWithFormat(
        surface, SurfaceFormat::B8G8R8A8);
    NS_ENSURE_TRUE(dataSurface, NS_ERROR_FAILURE);
    mappedOK = dataSurface->Map(DataSourceSurface::MapType::READ, &map);
  } else {
    dataSurface = surface->GetDataSurface();
    NS_ENSURE_TRUE(dataSurface, NS_ERROR_FAILURE);
    mappedOK = dataSurface->Map(DataSourceSurface::MapType::READ, &map);
  }
  NS_ENSURE_TRUE(dataSurface && mappedOK, NS_ERROR_FAILURE);
  MOZ_ASSERT(dataSurface->GetFormat() == SurfaceFormat::B8G8R8A8);

  uint8_t* data = nullptr;
  UniquePtr<uint8_t[]> autoDeleteArray;
  if (map.mStride == BytesPerPixel(dataSurface->GetFormat()) * iconSize.width) {
    // Mapped data is already packed
    data = map.mData;
  } else {
    // We can't use map.mData since the pixels are not packed (as required by
    // CreateDIBitmap, which is called under the DataToBitmap call below).
    //
    // We must unmap before calling SurfaceToPackedBGRA because it needs access
    // to the pixel data.
    dataSurface->Unmap();
    map.mData = nullptr;

    autoDeleteArray = SurfaceToPackedBGRA(dataSurface);
    data = autoDeleteArray.get();
    NS_ENSURE_TRUE(data, NS_ERROR_FAILURE);
  }

  HBITMAP bmp = DataToBitmap(data, iconSize.width, -iconSize.height, 32);
  uint8_t* a1data = Data32BitTo1Bit(data, iconSize.width, iconSize.height);
  if (map.mData) {
    dataSurface->Unmap();
  }
  if (!a1data) {
    return NS_ERROR_FAILURE;
  }

  HBITMAP mbmp = DataToBitmap(a1data, iconSize.width, -iconSize.height, 1);
  free(a1data);

  ICONINFO info = {0};
  info.fIcon = !aIsCursor;
  info.xHotspot = aHotspot.x;
  info.yHotspot = aHotspot.y;
  info.hbmMask = mbmp;
  info.hbmColor = bmp;

  HCURSOR icon = ::CreateIconIndirect(&info);
  ::DeleteObject(mbmp);
  ::DeleteObject(bmp);
  if (!icon) return NS_ERROR_FAILURE;
  *aIcon = icon;
  return NS_OK;
}

// Adjust cursor image data
uint8_t* nsWindowGfx::Data32BitTo1Bit(uint8_t* aImageData, uint32_t aWidth,
                                      uint32_t aHeight) {
  // We need (aWidth + 7) / 8 bytes plus zero-padding up to a multiple of
  // 4 bytes for each row (HBITMAP requirement). Bug 353553.
  uint32_t outBpr = ((aWidth + 31) / 8) & ~3;

  // Allocate and clear mask buffer
  uint8_t* outData = (uint8_t*)calloc(outBpr, aHeight);
  if (!outData) return nullptr;

  int32_t* imageRow = (int32_t*)aImageData;
  for (uint32_t curRow = 0; curRow < aHeight; curRow++) {
    uint8_t* outRow = outData + curRow * outBpr;
    uint8_t mask = 0x80;
    for (uint32_t curCol = 0; curCol < aWidth; curCol++) {
      // Use sign bit to test for transparency, as alpha byte is highest byte
      if (*imageRow++ < 0) *outRow |= mask;

      mask >>= 1;
      if (!mask) {
        outRow++;
        mask = 0x80;
      }
    }
  }

  return outData;
}

/**
 * Convert the given image data to a HBITMAP. If the requested depth is
 * 32 bit, a bitmap with an alpha channel will be returned.
 *
 * @param aImageData The image data to convert. Must use the format accepted
 *                   by CreateDIBitmap.
 * @param aWidth     With of the bitmap, in pixels.
 * @param aHeight    Height of the image, in pixels.
 * @param aDepth     Image depth, in bits. Should be one of 1, 24 and 32.
 *
 * @return The HBITMAP representing the image. Caller should call
 *         DeleteObject when done with the bitmap.
 *         On failure, nullptr will be returned.
 */
HBITMAP nsWindowGfx::DataToBitmap(uint8_t* aImageData, uint32_t aWidth,
                                  uint32_t aHeight, uint32_t aDepth) {
  HDC dc = ::GetDC(nullptr);

  if (aDepth == 32) {
    // Alpha channel. We need the new header.
    BITMAPV4HEADER head = {0};
    head.bV4Size = sizeof(head);
    head.bV4Width = aWidth;
    head.bV4Height = aHeight;
    head.bV4Planes = 1;
    head.bV4BitCount = aDepth;
    head.bV4V4Compression = BI_BITFIELDS;
    head.bV4SizeImage = 0;  // Uncompressed
    head.bV4XPelsPerMeter = 0;
    head.bV4YPelsPerMeter = 0;
    head.bV4ClrUsed = 0;
    head.bV4ClrImportant = 0;

    head.bV4RedMask = 0x00FF0000;
    head.bV4GreenMask = 0x0000FF00;
    head.bV4BlueMask = 0x000000FF;
    head.bV4AlphaMask = 0xFF000000;

    HBITMAP bmp = ::CreateDIBitmap(
        dc, reinterpret_cast<CONST BITMAPINFOHEADER*>(&head), CBM_INIT,
        aImageData, reinterpret_cast<CONST BITMAPINFO*>(&head), DIB_RGB_COLORS);
    ::ReleaseDC(nullptr, dc);
    return bmp;
  }

  char reserved_space[sizeof(BITMAPINFOHEADER) + sizeof(RGBQUAD) * 2];
  BITMAPINFOHEADER& head = *(BITMAPINFOHEADER*)reserved_space;

  head.biSize = sizeof(BITMAPINFOHEADER);
  head.biWidth = aWidth;
  head.biHeight = aHeight;
  head.biPlanes = 1;
  head.biBitCount = (WORD)aDepth;
  head.biCompression = BI_RGB;
  head.biSizeImage = 0;  // Uncompressed
  head.biXPelsPerMeter = 0;
  head.biYPelsPerMeter = 0;
  head.biClrUsed = 0;
  head.biClrImportant = 0;

  BITMAPINFO& bi = *(BITMAPINFO*)reserved_space;

  if (aDepth == 1) {
    RGBQUAD black = {0, 0, 0, 0};
    RGBQUAD white = {255, 255, 255, 0};

    bi.bmiColors[0] = white;
    bi.bmiColors[1] = black;
  }

  HBITMAP bmp =
      ::CreateDIBitmap(dc, &head, CBM_INIT, aImageData, &bi, DIB_RGB_COLORS);
  ::ReleaseDC(nullptr, dc);
  return bmp;
}