c# - 「こぼれ」のない影

Question

「こぼれる」ことなく、一方向にだけ進む影を作りたい。

左側と右側でわかるように、影は「こぼれています」が、影が側面ではなく上に上がるようにします。どうやってやるの？これは私がこれまでに持っているコードです:

<UserControl x:Class="Client.Views.CartItemToolBar"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         xmlns:ctrl="clr-namespace:Client.Controls"
         xmlns:local="clr-namespace:Client.Views"
         mc:Ignorable="d">
<Grid Height="56" Background="{StaticResource color_white}" Margin="2,0">
    <Border Background="Transparent" BorderBrush="{Binding Path=Background, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Grid}}" BorderThickness="0,10,0,0">
        <Border.Effect>
            <DropShadowEffect ShadowDepth="0" BlurRadius="16" Direction="90" />
        </Border.Effect>
    </Border>
    <StackPanel Orientation="Horizontal" Background="{Binding Path=Background, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Grid}}">
        <ctrl:TestButton Style="{StaticResource ButtonCartPositionAction}" PosAction="CartItem/Minus">
            <ctrl:IconViewbox IconData="{StaticResource IconPathNumericNegative1}" IconSize="20" RenderTransformOrigin="0.5,0.5" >
                <ctrl:IconViewbox.RenderTransform>
                    <TransformGroup>
                        <ScaleTransform/>
                        <SkewTransform/>
                        <RotateTransform/>
                        <TranslateTransform X="-4" Y="-4"/>
                    </TransformGroup>
                </ctrl:IconViewbox.RenderTransform>
            </ctrl:IconViewbox>
        </ctrl:TestButton>
        <ctrl:TestButton Style="{StaticResource ButtonCartPositionAction}" PosAction="CartItem/Plus" >
            <ctrl:IconViewbox IconData="{StaticResource IconPathNumericPositive1}" IconSize="20" RenderTransformOrigin="0.5,0.5" >
                <ctrl:IconViewbox.RenderTransform>
                    <TransformGroup>
                        <ScaleTransform/>
                        <SkewTransform/>
                        <RotateTransform/>
                        <TranslateTransform X="-4" Y="-4"/>
                    </TransformGroup>
                </ctrl:IconViewbox.RenderTransform>
            </ctrl:IconViewbox>
        </ctrl:TestButton>
        <ctrl:TestButton Style="{StaticResource ButtonCartPositionAction}" Content="Change Price" PosAction="CartItem/ChangePrice" />
        <ctrl:TestButton Style="{StaticResource ButtonCartPositionAction}" PosAction="UI/SwitchTo/CartItemDiscount">
            <Grid>
                <Label Margin="0" Padding="0">Pos Discount</Label>                    
            </Grid>
        </ctrl:TestButton>            
        <ctrl:TestButton Style="{StaticResource ButtonCartPositionAction}" PosAction="CartItem/Remove">
            <ctrl:IconViewbox IconData="{StaticResource IconPathTrashCan}" IconSize="20" />
        </ctrl:TestButton>
    </StackPanel>        
</Grid>