为什么我的坐标(1,1)从(0，1)开始? [英] Why my coordinate (1,1) start at (0, 1)?

问题描述

我重写了Border控件，并在重写的OnRender中执行了

I overriden Border control and in my overriden OnRender I do:

protected override void OnRender(System.Windows.Media.DrawingContext dc)
        {
            this.SnapsToDevicePixels = true;
            this.VisualEdgeMode = EdgeMode.Aliased;
            var myPen = new Pen(new SolidColorBrush(Colors.LightGray), 1);
            dc.DrawLine(myPen, new Point(1, 1), new Point(1, RenderSize.Height - 1));
            return;

哪个给我这个结果:

Which give me this result:

问题:

有人可以告诉我为什么我的代码画一条以(0,1)开头的行，而假定它以(1，1)开头，就像用代码编写的那样吗?

我的DPI是96、96.

My DPI are 96, 96.

对于裁判，这是我的xaml:

For ref, this is my xaml:

<Window xmlns:MyControls="clr-namespace:MyControls;assembly=MyControls"  x:Class="TestControls.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"></RowDefinition>
            <RowDefinition></RowDefinition>
            <RowDefinition></RowDefinition>
        </Grid.RowDefinitions>

        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto"></ColumnDefinition>
            <ColumnDefinition></ColumnDefinition>
            <ColumnDefinition></ColumnDefinition>
        </Grid.ColumnDefinitions>


        <MyControls:Border3D BorderThickness="3" BorderBrush="Aqua">
            <Rectangle Width="74" Height="3" HorizontalAlignment="Left">
                <Rectangle.Fill>
                    <SolidColorBrush Color="#40FF0000">

                    </SolidColorBrush>
                </Rectangle.Fill>
            </Rectangle>
        </MyControls:Border3D>

        <Rectangle  Grid.Row="1" Grid.Column="0" Width="80" Grid.ColumnSpan="2" HorizontalAlignment="Left">
            <Rectangle.Fill>
                <SolidColorBrush Color="LightGray"></SolidColorBrush>
            </Rectangle.Fill>
        </Rectangle>

    </Grid>
</Window>

推荐答案

请记住，(0, 0)不在左上像素的中心.相反，它是该像素的左上角.为了在第二个像素列(索引为1)的中间绘制笔划粗细为1的线，您必须从(1.5, 1)绘制到(1.5, RenderSize.Height - 1):

Keep in mind that (0, 0) is not the center of the upper left pixel. Instead it is the upper left corner of that pixel. In order to draw a line with a stroke thickness of 1 in the middle of the second pixel column (with index 1) you would have to draw from (1.5, 1) to (1.5, RenderSize.Height - 1):

dc.DrawLine(myPen, new Point(1.5, 1), new Point(1.5, RenderSize.Height - 1));

设置SnapsToDevicePixels = true使您的行向左对齐半个像素.

Setting SnapsToDevicePixels = true made your line snap to the left by half a pixel.

如果您使用 PenLineCap.Square 对于线条的Pen的StartLineCap和EndLineCap属性，您可以从一个像素中心精确地绘制到另一个像素中心:

If you would use PenLineCap.Square for both the StartLineCap and EndLineCap properties of the line's Pen, you could draw from exactly one pixel center to the other:

var myPen = new Pen(Brushes.LightGray, 1);
myPen.StartLineCap = PenLineCap.Square;
myPen.EndLineCap = PenLineCap.Square;
dc.DrawLine(myPen, new Point(1.5, 1.5), new Point(1.5, RenderSize.Height - 1.5));

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