我如何清除的Direct2D渲染目标，以完全透明 [英] How do I clear a Direct2D render target to fully transparent

问题描述

我试图借鉴一种无形的HWND半透明矩形。但是，清除与ID2D1HwndRenderTarget ::清除窗口只是使整个窗口黑色的，所以当我画在上面的矩形，它们看起来半黑的。

I'm trying to draw semi-transparent rectangles on an invisible HWND. However, clearing the window with ID2D1HwndRenderTarget::Clear just makes the entire window black, so when I draw rectangles on top, they look semi-black.

如果我不清除（）和不画，则该窗口是看不见的，因为它应该是。清除（）是这里的罪魁祸首;但是如果我不使用它，然后画严重打乱了pretty。

If I don't Clear() and don't draw, then the window is invisible, as it should be. Clear() is the culprit here; however if I don't use it then painting messes up pretty badly.

这里的code，我用我的WindowProc：

Here's the code I'm using in my WindowProc:

case WM_PAINT:
    // Begin drawing
    pRenderTarget->BeginDraw();
    pRenderTarget->SetTransform(D2D1::Matrix3x2F::Identity());

    // Clear the window
    pRenderTarget->Clear();

    // Paint the panel and its children
    D2DSurface()->StartPainting();
    {
        D2DSurface()->PaintTraverse(panel);
    }
    D2DSurface()->FinishPainting();

    // Finish drawing
    HRESULT hr = plat->pRenderTarget->EndDraw();

在此先感谢！

推荐答案

在创建的RenderTarget，你必须告诉您要使用阿尔法（以premultiplied模式）的像素格式D2D：

When creating your RenderTarget, you'll have to tell D2D that you want to use alpha (in premultiplied mode) in the pixel format:

  HRESULT hr = mD2DFactory->CreateHwndRenderTarget(
    D2D1::RenderTargetProperties( D2D1_RENDER_TARGET_TYPE_DEFAULT, D2D1::PixelFormat( DXGI_FORMAT_UNKNOWN, D2D1_ALPHA_MODE_PREMULTIPLIED ) ),
    D2D1::HwndRenderTargetProperties( mWindow, size ),
    &mRenderTarget );

在此之后，调用清除（）为零的Alpha值的作品就好。

After this, calling Clear() with an alpha value of zero works just fine.

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