WPF 中 glOrtho 的等价物

Question

在 OpenGL 中我可以这样做：

glOrtho(-10, 10, -10, 10, -1, 1)

建立一个坐标系，其中x的范围是-10到10，y的范围是-10到10。

有没有办法在 WPF 中改变画布的坐标系？

Answer 1

我在 Canvas 上创建了一个扩展方法，允许您设置笛卡尔坐标系。一个示例调用是：

canvas.SetCoordinateSystem(-10, 10, -10, 10)

这将设置canvas 的坐标系，使x 从-10 变为10，y 从-10 变为10。

扩展方法如下：

public static Canvas SetCoordinateSystem(this Canvas canvas, Double xMin, Double xMax, Double yMin, Double yMax)
{
    var width = xMax - xMin;
    var height = yMax - yMin;

    var translateX = -xMin;
    var translateY = height + yMin;

    var group = new TransformGroup();

    group.Children.Add(new TranslateTransform(translateX, -translateY));
    group.Children.Add(new ScaleTransform(canvas.ActualWidth / width, canvas.ActualHeight / -height));

    canvas.RenderTransform = group;

    return canvas;
}

这是一个演示程序，它在画布上绘制 Sin(x) 以及 X 和 Y 轴：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace CanvasScale
{
    public static class CanvasUtils
    {
        public static Canvas SetCoordinateSystem(this Canvas canvas, Double xMin, Double xMax, Double yMin, Double yMax)
        {
            var width = xMax - xMin;
            var height = yMax - yMin;

            var translateX = -xMin;
            var translateY = height + yMin;

            var group = new TransformGroup();

            group.Children.Add(new TranslateTransform(translateX, -translateY));
            group.Children.Add(new ScaleTransform(canvas.ActualWidth / width, canvas.ActualHeight / -height));

            canvas.RenderTransform = group;

            return canvas;
        }
    }

    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            var canvas = new Canvas();

            Content = canvas;

            SizeChanged += (s, e) => canvas.SetCoordinateSystem(-10, 10, -10, 10);                

            canvas.Children.Add(new Line() { X1 = -10, Y1 = 0, X2 = 10, Y2 = 0, Stroke = Brushes.Black, StrokeThickness = 0.2 });
            canvas.Children.Add(new Line() { X1 = 0, Y1 = -10, X2 = 0, Y2 = 10, Stroke = Brushes.Black, StrokeThickness = 0.2 });

            var polyline = new Polyline()
            {
                Stroke = Brushes.BurlyWood,
                StrokeThickness = 0.1,
                Points = new PointCollection()
            };

            for (var x = -10.0; x <= 10.0; x += 0.1)
                polyline.Points.Add(new Point(x, Math.Sin(x)));

            canvas.Children.Add(polyline);
        }
    }
}

它是这样的：

Answer 2

OrthographicCamera 提供正交投影，而不是更常见的透视投影 (PerspectiveCamera)。

要确定从相机可见的坐标“范围”，您可能需要调整Width 和Position 属性。

Answer 3

只要您没有同时设置 Canvas.Top、Canvas.Left、Canvas.Right 或 Canvas.Bottom 属性，您可以将 Canvas 中每个子项的 LayoutTransform 或 RenderTransform 属性设置为适当的TransformGroup 或MatrixTransform：

Rect viewport = new Rect(-10, -10, 20, 20);
double scaleX = ActualWidth / viewport.Width;
double scaleY = ActualHeight / viewport.Height;
RenderTransform = new MatrixTransform(
    scaleX, 0d, 0d, scaleY, -viewport.X * scaleX, -viewport.Y * scaleY);