c# - UWP - 如何平铺背景图像？

Question

在通用 Windows 应用程序中，我尝试使用背景图像(来自 ImageSource)并将其平铺在控件上。

XAML

<Grid x:Name="gridBackground">
  <ContentPresenter />
</Grid>

C#

void UpdateBackground(ImageSource source)
{
// ...
  gridBackground.Background = new ImageBrush {
    ImageSource = source,
    Stretch = Stretch.None
  };
}

根据 MSDN ,ImageBrush继承自TileBrush。它甚至说:

Use for an ImageBrush include decorative effects for text, or tiled backgrounds for controls or layout containers.

如果禁用拉伸(stretch)，我会假设这应该平铺图像，但是，唉，它只是在控件的中间绘制图像。我没有看到任何使其平铺的实际属性。

在WPF中，有一个TileMode可以设置属性和 ViewPort 来指定图 block 的尺寸。但这在通用平台下似乎不存在。

A previous question指的是 WinRT (Windows 8)，但我希望有一个基于画笔的解决方案，而不是用图像填充 Canvas 。

如何使用 UWP 平铺背景图像？

Answer 1

A previous question refers to WinRT (Windows 8), but I'm hoping for a brush based solution, rather than filling a canvas with images.

目前，在 UWP 应用程序中以平铺模式显示背景图像只有两种解决方案，您知道的第一种是填充 Canvas 。

我使用的第二个是创建一个 Panel 并在其上绘制图像，这个想法源自 this article

此方法的作用是滥用我们在矩形中绘制重复线组的事实。首先，它尝试在顶部绘制一个与我们的图 block 高度相同的 block 。然后它向下复制该 block ，直到它到达底部。

我修改了一些代码并修复了一些问题:

public class TiledBackground : Panel
{
        public ImageSource BackgroundImage
        {
            get { return (ImageSource)GetValue(BackgroundImageProperty); }
            set { SetValue(BackgroundImageProperty, value); }
        }

        // Using a DependencyProperty as the backing store for BackgroundImage.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty BackgroundImageProperty =
            DependencyProperty.Register("BackgroundImage", typeof(ImageSource), typeof(TiledBackground), new PropertyMetadata(null, BackgroundImageChanged));


        private static void BackgroundImageChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ((TiledBackground)d).OnBackgroundImageChanged();
        }
        private static void DesignDataChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ((TiledBackground)d).OnDesignDataChanged();
        }

        private ImageBrush backgroundImageBrush = null;

        private bool tileImageDataRebuildNeeded = true;
        private byte[] tileImagePixels = null;
        private int tileImageWidth = 0;
        private int tileImageHeight = 0;

        private readonly BitmapPixelFormat bitmapPixelFormat = BitmapPixelFormat.Bgra8;
        private readonly BitmapTransform bitmapTransform = new BitmapTransform();
        private readonly BitmapAlphaMode bitmapAlphaMode = BitmapAlphaMode.Straight;
        private readonly ExifOrientationMode exifOrientationMode = ExifOrientationMode.IgnoreExifOrientation;
        private readonly ColorManagementMode coloManagementMode = ColorManagementMode.ColorManageToSRgb;

        public TiledBackground()
        {
            this.backgroundImageBrush = new ImageBrush();
            this.Background = backgroundImageBrush;

            this.SizeChanged += TiledBackground_SizeChanged;
        }

        private async void TiledBackground_SizeChanged(object sender, SizeChangedEventArgs e)
        {
            await this.Render((int)e.NewSize.Width, (int)e.NewSize.Height);
        }

        private async void OnBackgroundImageChanged()
        {
            tileImageDataRebuildNeeded = true;
            await Render((int)this.ActualWidth, (int)this.ActualHeight);
        }

        private async void OnDesignDataChanged()
        {
            tileImageDataRebuildNeeded = true;
            await Render((int)this.ActualWidth, (int)this.ActualHeight);
        }

        private async Task RebuildTileImageData()
        {
            BitmapImage image = BackgroundImage as BitmapImage;
            if ((image != null) && (!DesignMode.DesignModeEnabled))
            {
                string imgUri = image.UriSource.OriginalString;
                if (!imgUri.Contains("ms-appx:///"))
                {
                    imgUri += "ms-appx:///";
                }
                var imageSource = new Uri(imgUri);
                StorageFile storageFile = await StorageFile.GetFileFromApplicationUriAsync(imageSource);
                using (var imageStream = await storageFile.OpenAsync(FileAccessMode.Read))
                {
                    BitmapDecoder decoder = await BitmapDecoder.CreateAsync(imageStream);

                    var pixelDataProvider = await decoder.GetPixelDataAsync(this.bitmapPixelFormat, this.bitmapAlphaMode,
                        this.bitmapTransform, this.exifOrientationMode, this.coloManagementMode
                        );

                    this.tileImagePixels = pixelDataProvider.DetachPixelData();
                    this.tileImageHeight = (int)decoder.PixelHeight;
                    this.tileImageWidth = (int)decoder.PixelWidth;
                }
            }
        }

        private byte[] CreateBackgroud(int width, int height)
        {
            int bytesPerPixel = this.tileImagePixels.Length / (this.tileImageWidth * this.tileImageHeight);
            byte[] data = new byte[width * height * bytesPerPixel];

            int y = 0;
            int fullTileInRowCount = width / tileImageWidth;
            int tileRowLength = tileImageWidth * bytesPerPixel;

            //Stage 1: Go line by line and create a block of our pattern
            //Stop when tile image height or required height is reached
            while ((y < height) && (y < tileImageHeight))
            {
                int tileIndex = y * tileImageWidth * bytesPerPixel;
                int dataIndex = y * width * bytesPerPixel;

                //Copy the whole line from tile at once
                for (int i = 0; i < fullTileInRowCount; i++)
                {
                    Array.Copy(tileImagePixels, tileIndex, data, dataIndex, tileRowLength);
                    dataIndex += tileRowLength;
                }

                //Copy the rest - if there is any
                //Length will evaluate to 0 if all lines were copied without remainder
                Array.Copy(tileImagePixels, tileIndex, data, dataIndex,
                           (width - fullTileInRowCount * tileImageWidth) * bytesPerPixel);
                y++; //Next line
            }

            //Stage 2: Now let's copy those whole blocks from top to bottom
            //If there is not enough space to copy the whole block, skip to stage 3
            int rowLength = width * bytesPerPixel;
            int blockLength = this.tileImageHeight * rowLength;

            while (y <= (height - tileImageHeight))
            {
                int dataBaseIndex = y * width * bytesPerPixel;
                Array.Copy(data, 0, data, dataBaseIndex, blockLength);
                y += tileImageHeight;
            }

            //Copy the rest line by line
            //Use previous lines as source
            for (int row = y; row < height; row++)
                Array.Copy(data, (row - tileImageHeight) * rowLength, data, row * rowLength, rowLength);

            return data;
        }

        private async Task Render(int width, int height)
        {
            Stopwatch fullsw = Stopwatch.StartNew();

            if (tileImageDataRebuildNeeded)
                await RebuildTileImageData();

            if ((height > 0) && (width > 0))
            {
                using (var randomAccessStream = new InMemoryRandomAccessStream())
                {
                    Stopwatch sw = Stopwatch.StartNew();
                    var backgroundPixels = CreateBackgroud(width, height);
                    sw.Stop();
                    Debug.WriteLine("Background generation finished: {0} ticks - {1} ms", sw.ElapsedTicks, sw.ElapsedMilliseconds);

                    BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.PngEncoderId, randomAccessStream);
                    encoder.SetPixelData(this.bitmapPixelFormat, this.bitmapAlphaMode, (uint)width, (uint)height, 96, 96, backgroundPixels);
                    await encoder.FlushAsync();

                    if (this.backgroundImageBrush.ImageSource == null)
                    {
                        BitmapImage bitmapImage = new BitmapImage();
                        randomAccessStream.Seek(0);
                        bitmapImage.SetSource(randomAccessStream);
                        this.backgroundImageBrush.ImageSource = bitmapImage;
                    }
                    else ((BitmapImage)this.backgroundImageBrush.ImageSource).SetSource(randomAccessStream);
                }
            }
            else this.backgroundImageBrush.ImageSource = null;

            fullsw.Stop();
            Debug.WriteLine("Background rendering finished: {0} ticks - {1} ms", fullsw.ElapsedTicks, fullsw.ElapsedMilliseconds);
        }
}

用法:

<Grid x:Name="rootGrid" Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <tileCtrl:TiledBackground
                               BackgroundImage="Assets/avatar1.png"
                               Width="{Binding ActualWidth, ElementName=rootGrid}" Height="{Binding ActualHeight, ElementName=rootGrid}"/>
    </Grid>

查看解决方案 Github