IDWriteBitmapRenderTarget interface (dwrite.h)

Article
02/22/2024

Encapsulates a 32-bit device independent bitmap and device context, which can be used for rendering glyphs.

Inheritance

The IDWriteBitmapRenderTarget interface inherits from the IUnknown interface. IDWriteBitmapRenderTarget also has these types of members:

Methods

The IDWriteBitmapRenderTarget interface has these methods.


IDWriteBitmapRenderTarget::DrawGlyphRun Draws a run of glyphs to a bitmap target at the specified position.
IDWriteBitmapRenderTarget::GetCurrentTransform Gets the transform that maps abstract coordinates to DIPs. By default this is the identity transform. Note that this is unrelated to the world transform of the underlying device context.
IDWriteBitmapRenderTarget::GetMemoryDC Gets a handle to the memory device context.
IDWriteBitmapRenderTarget::GetPixelsPerDip Gets the number of bitmap pixels per DIP.
IDWriteBitmapRenderTarget::GetSize Gets the dimensions of the target bitmap.
IDWriteBitmapRenderTarget::Resize Resizes the bitmap.
IDWriteBitmapRenderTarget::SetCurrentTransform Sets the transform that maps abstract coordinate to DIPs (device-independent pixel). This does not affect the world transform of the underlying device context.
IDWriteBitmapRenderTarget::SetPixelsPerDip Sets the number of bitmap pixels per DIP (device-independent pixel). A DIP is 1/96 inch, so this value is the number if pixels per inch divided by 96.

Remarks

You create an IDWriteBitmapRenderTarget by using the IDWriteGdiInterop::CreateBitmapRenderTarget method, as shown in the following code.

if (SUCCEEDED(hr))
{
    hr = g_pGdiInterop->CreateBitmapRenderTarget(hdc, r.right, r.bottom, &g_pBitmapRenderTarget);
}

IDWriteGdiInterop::CreateBitmapRenderTarget takes a handle to a DC and the desired width and height. In the above example, the width and height given are the size of the window rect.

Rendering

One way to use a IDWriteBitmapRenderTarget, for rendering to a bitmap, is to implement a custom renderer interface derived from the IDWriteTextRenderer interface. In your implementation of the DrawGlyphRun method of your custom renderer, call the IDWriteBitmapRenderTarget::DrawGlyphRun method to draw the glyphs as shown in the following code.

STDMETHODIMP GdiTextRenderer::DrawGlyphRun(
    __maybenull void* clientDrawingContext,
    FLOAT baselineOriginX,
    FLOAT baselineOriginY,
    DWRITE_MEASURING_MODE measuringMode,
    __in DWRITE_GLYPH_RUN const* glyphRun,
    __in DWRITE_GLYPH_RUN_DESCRIPTION const* glyphRunDescription,
    IUnknown* clientDrawingEffect
    )
{
    HRESULT hr = S_OK;

    // Pass on the drawing call to the render target to do the real work.
    RECT dirtyRect = {0};

    hr = pRenderTarget_->DrawGlyphRun(
        baselineOriginX,
        baselineOriginY,
        measuringMode,
        glyphRun,
        pRenderingParams_,
        RGB(0,200,255),
        &dirtyRect
        );
    

    return hr;
}

The IDWriteBitmapRenderTarget encapsulates and renders to a bitmap in memory. The GetMemoryDC function returns a handle to the device context of this bitmap.

Requirements

Requirement	Value
Minimum supported client	Windows 7, Windows Vista with SP2 and Platform Update for Windows Vista [desktop apps \| UWP apps]
Minimum supported server	Windows Server 2008 R2, Windows Server 2008 with SP2 and Platform Update for Windows Server 2008 [desktop apps \| UWP apps]
Target Platform	Windows
Header	dwrite.h

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