c# - 从点列表下载相交但不复制 map 下载图 block ？

Question

我有一个 WPF 用户控件，用户可以使用它在 map Canvas 上绘制一个矩形来定义一个区域，用于从 Web 服务下载背景图像图 block 。瓷砖的经纬度为 1x1 度。

这是有效的，我将一个点作为参数传递并下载磁贴。但是我现在正试图通过 List<Point>对于用户定义矩形的每个角，因此确定哪些图 block 与每个点相交。这在一定程度上是有效的，但是如果用户在单个图 block 中完全定义了一个矩形，那么同一个图 block 将被下载 4 次(每个点一次):

ForEach(point in rectanglePointsList)
 {
   DownloadTile(point);
 }

我需要遍历这些点并确定是否下载后续图 block 。这段代码对瓷砖来说是愚蠢的，我只有传入的点参数。一位同事建议使用嵌套的 for 循环，我可以从每个点转换 X 和 Y，找到最小值和最大值，然后以某种方式确定是否知道瓷砖总是 1x1 度的瓷砖应该被下载。有没有算法可以实现这个？真的不知道从哪里开始。

List<int>xValuesList = new List<int>();
List<int> yValuesList = new List<int>();

ForEach(point in RectanglePointsList)
 {
   xValuesList.Add(Convert.ToInt32(point.X);
   yValuesList.Add(Convert.ToInt32(point.Y);
 }

 int maxX = xValuesList.Select(value => value.X).Max();
 int maxY = yValuesList.Select(value => value.Y).Max();

 //Lost after here...

Answer 1

这是一个快速示例 :D

• 选择一组图 block
• 是否将它们添加到缓存
• 已添加或未添加的节目
• 支持鼠标单击，无需画矩形
• 无论您从哪里开始/结束，都包含选定的图 block

这里我点击了前两个，这次我画了一个包含下面两个的矩形，它们没有被添加两次。

XAML:

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:local="clr-namespace:WpfApplication1"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        x:Name="Window"
        Title="MainWindow"
        Width="525"
        Height="350"
        Background="Transparent"
        SnapsToDevicePixels="True"
        UseLayoutRounding="True"
        mc:Ignorable="d">
    <Grid />
</Window>

代码:

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows;
using System.Windows.Input;
using System.Windows.Media;

namespace WpfApplication1
{
    public partial class MainWindow : Window
    {
        private readonly HashSet<Int32Point> _set = new HashSet<Int32Point>();
        private readonly int columns = 10;
        private readonly int rows = 10;
        private bool _down;
        private Point _position1;
        private Point _position2;
        private Size size = new Size(500, 500);

        public MainWindow()
        {
            InitializeComponent();
            MouseDown += MainWindow_MouseDown;
            MouseMove += MainWindow_MouseMove;
            MouseUp += MainWindow_MouseUp;
        }

        private void MainWindow_MouseUp(object sender, MouseButtonEventArgs e)
        {
            _down = false;
            InvalidateVisual();

            // find rects selected
            var x1 = (int) Math.Floor(_position1.X/(size.Width/columns));
            var y1 = (int) Math.Floor(_position1.Y/(size.Height/rows));
            var x2 = (int) Math.Ceiling(_position2.X/(size.Width/columns));
            var y2 = (int) Math.Ceiling(_position2.Y/(size.Height/rows));
            var w = x2 - x1;
            var h = y2 - y1;

            var builder = new StringBuilder();
            for (var y = 0; y < h; y++)
            {
                for (var x = 0; x < w; x++)
                {
                    var int32Point = new Int32Point(x1 + x, y1 + y);
                    var add = _set.Add(int32Point);
                    if (add)
                    {
                        // download image !!!
                    }
                    else
                    {
                        // image already downloaded, do something !
                    }
                    builder.AppendLine(string.Format("{0} : {1}", int32Point, (add ? "added" : "ignored")));
                }
            }
            MessageBox.Show(builder.ToString());
        }

        private void MainWindow_MouseMove(object sender, MouseEventArgs e)
        {
            _position2 = e.GetPosition(this);
            InvalidateVisual();
        }

        private void MainWindow_MouseDown(object sender, MouseButtonEventArgs e)
        {
            _position1 = e.GetPosition(this);
            _down = true;
        }

        protected override void OnRenderSizeChanged(SizeChangedInfo sizeInfo)
        {
            InvalidateVisual();
        }

        protected override void OnRender(DrawingContext drawingContext)
        {
            // draw a mini-map
            for (var y = 0; y < rows; y++)
            {
                for (var x = 0; x < columns; x++)
                {
                    var color = Color.FromRgb((byte) ((double) x/columns*255), (byte) ((double) y/rows*255), 255);
                    var brush = new SolidColorBrush(color);
                    var w = size.Width/columns;
                    var h = size.Height/rows;
                    var rect = new Rect(w*x, h*y, w, h);
                    drawingContext.DrawRectangle(brush, null, rect);
                }
            }

            // draw selection rectangle
            if (_down)
            {
                drawingContext.DrawRectangle(null, new Pen(new SolidColorBrush(Colors.White), 2.0),
                    new Rect(_position1, _position2));
            }
        }

        private struct Int32Point
        {
            public readonly int X, Y;

            public Int32Point(int x, int y)
            {
                X = x;
                Y = y;
            }

            public override string ToString()
            {
                return $"X: {X}, Y: {Y}";
            }
        }
    }
}

继续改进!