We can change the color of a text range by passing a brush object to IDWriteTextLayout::SetDrawingEffect. Here is a simple example.

An example of using IDWriteTextLayout::SetDrawingEffect

LRESULT CDirectWriteDemoView::OnDraw2D(WPARAM wParam, LPARAM lParam)
{
   CHwndRenderTarget* pRenderTarget = (CHwndRenderTarget*)lParam;

   // Please, see the demo application for more details.
   // ...

   // init color effects 
   _InitColorEffects(pRenderTarget, spTextLayout);

   // Draw the text in the render target.
   pRenderTarget->DrawTextLayout(CD2DPointF(),         // upper-left corner of the text 
                                 spTextLayout.get(),   // text layout object
                                 &CD2DSolidColorBrush  // default brush used for text
                                 (pRenderTarget, 
                                 D2D1::ColorF(D2D1::ColorF::Black))); 
   return 0;
}

void CDirectWriteDemoView::_InitColorEffects(CHwndRenderTarget* pRenderTarget, 
                                   std::shared_ptr<CD2DTextLayout> spTextLayout)
{
   CDirectWriteDemoDoc* pDoc = _GetDocument();
   DWRITE_TEXT_RANGE textRange;

   if(pDoc->FindTextRange(_T("BLUE"), textRange))
       _SetTextLayoutDrawingEffect(pRenderTarget, spTextLayout, 
                                   D2D1::ColorF(D2D1::ColorF::Blue), textRange);

   if(pDoc->FindTextRange(_T("YELLOW"), textRange))
       _SetTextLayoutDrawingEffect(pRenderTarget, spTextLayout,
                                   D2D1::ColorF(D2D1::ColorF::Yellow), textRange);

   if(pDoc->FindTextRange(_T("RED"), textRange))
       _SetTextLayoutDrawingEffect(pRenderTarget, spTextLayout,
                                   D2D1::ColorF(D2D1::ColorF::Red), textRange);
}

void CDirectWriteDemoView::_SetTextLayoutDrawingEffect(CHwndRenderTarget* pRenderTarget, 
            std::shared_ptr<CD2DTextLayout> spTextLpayout,
            D2D1_COLOR_F color, DWRITE_TEXT_RANGE textRange)
{
    CD2DSolidColorBrush* pBrush = new CD2DSolidColorBrush(pRenderTarget, color);
    pBrush->Create(pRenderTarget);
    spTextLayout->Get()->SetDrawingEffect(static_cast<IUnknown*>(pBrush->Get()), textRange);
}

So far, there’s no much “special effects” in the above example. Although a little bit more difficult, it is possible to make more customized rendering like text highlighting, double/triple underline/strikethrough and so on. This will be the subject of a future article.

Demo application

Download: MFC Support for DirectWrite Demo - Part 6.zip (51)

MFC Support for DirectWrite (Part 6) – Effects

Resources and related articles

• MSDN: IDWriteTextLayout::SetDrawingEffect method
• Codexpert blog: Direc2D and DirectWrite topics