C ++ Direct2D徑向漸變筆刷

Question

您好，我正在使用Direct2D，並且正在使用“徑向漸變畫筆”，但是我被卡在一個地方。

我的徑向漸變筆刷代碼

struct SampleWindow：DesktopWindow

{
    //FOr Radial Gradient Brush

    ComPtr<ID2D1RadialGradientBrush> radialBrush;

    void CrateDeviceResources()
    {
        D2D1_GRADIENT_STOP stops[] =
        {
            {0.0f, COLOR_WHITE},
            {1.0f, COLOR_BLUE}
        };

        ComPtr<ID2D1GradientStopCollection> collection;
        m_target->CreateGradientStopCollection(stops, _countof(stops),collection.ReleaseAndGetAddressOf());

        D2D1_RADIAL_GRADIENT_BRUSH_PROPERTIES props = {};
        m_target->CreateRadialGradientBrush(props,collection.Get(),radialBrush.ReleaseAndGetAddressOf());
    }

    void Draw()
    {
        auto size = m_target->GetSize();
        radialBrush -> SetCenter(Point2F(size.width / 2.0f, size.height / 2.0f));
        radialBrush -> SetRadiusX(size.width / 2.0f);
        radialBrush -> SetRadiusY(size.height / 2.0f);

        auto rect = RectF(0.0f, 0.0f, size.width, size.height);
        m_target -> FillRectangle(rect,radialBrush.Get());
    }

    void MouseMoved(int x, int y, WPARAM)
    {
        auto centere = radialBrush->GetCenter();
        radialBrush->SetGradientOriginOffset(Point2F(x - centere.x, y - centere.y));
        Invalidate();
    }
}

當我使用此行時，在功能鼠標中移動

auto centere = radialBrush->GetCenter();

我的程序壞了告訴我

Access violation Exception

DesktopWindow類代碼為：

BEGIN_MSG_MAP()
        MESSAGE_HANDLER(WM_PAINT, PaintHandler)
        MESSAGE_HANDLER(WM_DESTROY, DestroyHandler)
        MESSAGE_HANDLER(WM_SIZE, SizeHandler)
        MESSAGE_HANDLER(WM_DISPLAYCHANGE, DisplayChangeHandler)
        MESSAGE_HANDLER(WM_MOUSEMOVE, MouseMovedHandler)
    END_MSG_MAP()

LRESULT MouseMovedHandler(UINT, WPARAM wParam, LPARAM lParam,BOOL &)
    {
        MouseMoved(GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam),wParam);
        return 0;
    }

     virtual void MouseMoved(int x, int y, WPARAM)
     {

     }

我將MouseMoved函數設為虛擬，以便可以在其他類中使用該函數。 我無法理解我在哪里做錯了，請更正我應該在我的代碼中進行更正的地方。

Answer 1

這個問題的答案是鼠標移動功能在初始化渲染目標之前出現，為避免此失敗，請使用此方法

LRESULT MouseMovedHandler(UINT, WPARAM wParam, LPARAM lParam,BOOL &)
    {
        if (m_target)
        {
            MouseMoved(GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam),wParam);
        }
        return 0;
    }

現在代碼可以正常運行