public void AddDirtyRect(Int32Rect dirtyRect){WritePreamble();if (_lockCount == 0){throw new InvalidOperationException(SR.Get(SRID.Image_MustBeLocked));}//// Sanitize the dirty rect.//dirtyRect.ValidateForDirtyRect("dirtyRect", _pixelWidth, _pixelHeight);if (dirtyRect.HasArea){MILSwDoubleBufferedBitmap.AddDirtyRect(_pDoubleBufferedBitmap,ref dirtyRect);_hasDirtyRects = true;}// Note: we do not call WritePostscript because we do not want to// raise change notifications until the writeable bitmap is unlocked.}

        [DllImport(DllImport.MilCore, EntryPoint = "MILSwDoubleBufferedBitmapAddDirtyRect", PreserveSig = false)]internal static extern void AddDirtyRect(SafeMILHandle /* CSwDoubleBufferedBitmap */ THIS_PTR,ref Int32Rect dirtyRect);

        private SafeMILHandle _pDoubleBufferedBitmap;   // CSwDoubleBufferedBitmap

HRESULT
MILSwDoubleBufferedBitmapAddDirtyRect(__in CSwDoubleBufferedBitmap * THIS_PTR,__in const MILRect *pRect)
{HRESULT hr = S_OK;UINT x = 0;UINT y = 0;UINT width = 0;UINT height = 0;CMilRectU rcDirty;CHECKPTR(THIS_PTR);CHECKPTR(pRect);IFC(IntToUInt(pRect->X, &x));IFC(IntToUInt(pRect->Y, &y));IFC(IntToUInt(pRect->Width, &width));IFC(IntToUInt(pRect->Height, &height));// Since we converted x, y, width, and height from ints, we can add them// together and remain within a UINT.rcDirty = CMilRectU(x, y, width, height, XYWH_Parameters);IFC(THIS_PTR->AddDirtyRect(&rcDirty));Cleanup:RRETURN(hr);
}

HRESULT
CSwDoubleBufferedBitmap::AddDirtyRect(__in const CMilRectU *prcDirty)
{HRESULT hr = S_OK;CMilRectU rcBounds(0, 0, m_width, m_height, XYWH_Parameters);CMilRectU rcDirty = *prcDirty;if (!rcDirty.IsEmpty()){// Each dirty rect will eventually be treated as a RECT, so we must// ensure that the Left, Right, Top, and Bottom values never exceed// INT_MAX.  We already restrict our dimensions to INT_MAX, so as// long as the dirty rect is fully within the bounds of the bitmap,// we are safe.if (!rcBounds.DoesContain(rcDirty)){IFC(E_INVALIDARG);}// Adding a dirty rect that spans the entire bitmap will simply// replace all existing dirty rects.if (rcDirty.IsEquivalentTo(rcBounds)){m_pDirtyRects[0] = rcBounds;m_numDirtyRects = 1;}else{// Check to see if one of the existing dirty rects fully contains the// new dirty rect.  If so, there is no need to add it.for (UINT i = 0; i < m_numDirtyRects; i++){if (m_pDirtyRects[i].DoesContain(rcDirty)){// No dirty list change - new dirty rect is already included.goto Cleanup;}}// Collapse existing dirty rects if we're about to exceed our maximum.if (m_numDirtyRects >= c_maxBitmapDirtyListSize){// Collapse dirty list to a single large rect (including new rect)while (m_numDirtyRects > 1){m_pDirtyRects[0].Union(m_pDirtyRects[--m_numDirtyRects]);}m_pDirtyRects[0].Union(rcDirty);Assert(m_numDirtyRects == 1);}else{m_pDirtyRects[m_numDirtyRects++] = rcDirty;}}}Cleanup:RRETURN(hr);
}

HRESULT
CSwDoubleBufferedBitmap::CopyForwardDirtyRects()
{HRESULT hr = S_OK;IWGXBitmapSource *pIWGXBitmapSource = NULL;IWGXBitmapLock *pFrontBufferLock = NULL;UINT cbLockStride = 0;UINT cbBufferSize = 0;BYTE *pbSurface = NULL;Assert(m_pBackBuffer);// 根据调用 AddDirtyRect 方法加入的 DirtyRect 获取当前有哪些需要拷贝的像素// This locks only the rect specified as dirty for each copy. It would// be more efficient to just lock the entire rect once for all of the// copies, but then we need to manually compute offsets into the front// buffer specific to each pixel format.while (m_numDirtyRects > 0){// We have to jump through a few RECT hoops here since// IWGXBitmapSource::Lock/CopyPixels take a WICRect and// IWGXBitmap::AddDirtyRect takes a GDI RECT, neither of which are// CMilRectU which we use in CSwDoubleBufferedBitmap for geometric operations.//// CMilRectU and RECT share the same memory alignment, but different// signs.  Since we restrict the size of our bitmap to MAX_INT, we can// safely cast.// 这里只是做一层转换而已，拿到当前的一个 DirtyRect 范围const RECT *rcDirty = reinterpret_cast<RECT const *>(&m_pDirtyRects[--m_numDirtyRects]);WICRect copyRegion = {static_cast<int>(rcDirty->left),static_cast<int>(rcDirty->top),static_cast<int>(rcDirty->right - rcDirty->left),static_cast<int>(rcDirty->bottom - rcDirty->top)};// 根据 IWICBitmapSource 的使用文档，在使用之前需要先加上锁// This adds copyRegion as a dirty rect to m_pFrontBuffer automatically.IFC(m_pFrontBuffer->Lock(&copyRegion,MilBitmapLock::Write,&pFrontBufferLock));IFC(pFrontBufferLock->GetStride(&cbLockStride));IFC(pFrontBufferLock->GetDataPointer(&cbBufferSize, &pbSurface));// If a format converter has been allocated, it is necessary that we call copy// pixels through it rather than directly from the back buffer since its very// existence implies that a conversion is needed.GetPossiblyFormatConvertedBackBuffer(&pIWGXBitmapSource);// 这里的 IFC 是一个宏，表示的是如果返回值是 gg 的，那么 goto 到 Cleanup 标签/** #ifndef IFC#define IFC(x) { hr = (x); if (FAILED(hr)) goto Cleanup; }#endif*/// 下面代码就是核心逻辑，通过 CopyPixels 方法从后面的缓存也就是 WPF 层的数据拷贝到前面的缓存用于显示// 在这一层里面其实就丢失了 DirtyRect 信息IFC(pIWGXBitmapSource->CopyPixels(&copyRegion,cbLockStride,cbBufferSize,pbSurface));// 释放掉锁// We need to release the lock and format converter here because we are in a loop.ReleaseInterface(pIWGXBitmapSource);ReleaseInterface(pFrontBufferLock);}Cleanup:ReleaseInterfaceNoNULL(pIWGXBitmapSource);ReleaseInterfaceNoNULL(pFrontBufferLock);RRETURN(hr);
}