drawnui/drawnui.net/drawnui-pdf

<draw:SkiaLayout
    x:Class="MyApp.Reports.ReportView"
    x:DataType="vm:ReportViewModel"
    Type="Column"
    Padding="48"
    Spacing="28"
    BackgroundColor="White"
    HorizontalOptions="Fill">

const int Dpi = 150;
const float MarginInches = 0.3f;
static readonly TimeSpan ContentTimeout = TimeSpan.FromSeconds(15);
 
var scale = 1f;
var inches = Pdf.GetPaperSizeInInches(PaperFormat.A4);      // swap W/H for landscape
var paper = Pdf.GetPaperSizePixels(inches, Dpi);
var margins = MarginInches * Dpi;
var pageInner = new SKSize(paper.Width - margins * 2, paper.Height - margins * 2);
 
// 1. create, never attach to a Canvas
var content = new ReportView { BindingContext = data, HorizontalOptions = LayoutOptions.Fill };
 
// 2. measure at page width with unlimited height, warm up off the PDF
await WarmUpAsync(content, pageInner.Width, float.PositiveInfinity, scale);
 
// 3. page offsets that break between rows (needs the render tree from the warm-up)
var pages = Pdf.SplitStackToPages(content, isTemplated: true, pageInner, scale);
 
// 4. a window over the content: padding = margins, scroll = viewport
SkiaScroll viewport = null;
var wrapper = new SkiaLayout
{
    BindingContext = data,
    Padding = new Thickness(margins),
    HorizontalOptions = LayoutOptions.Fill,
    VerticalOptions = LayoutOptions.Fill,
    Children = new List<SkiaControl>
    {
        new SkiaScroll
        {
            BackgroundColor = Colors.White,
            HorizontalOptions = LayoutOptions.Fill,
            VerticalOptions = LayoutOptions.Fill,
            Content = content,
        }.Assign(out viewport)
    }
};
wrapper.Measure(paper.Width, paper.Height, scale);
wrapper.Arrange(new SKRect(0, 0, paper.Width, paper.Height),
    wrapper.MeasuredSize.Pixels.Width, wrapper.MeasuredSize.Pixels.Height, scale);
 
// 5. the document: pages in POINTS, canvas scaled from our dpi
var pagePoints = new SKSize(inches.Width * 72, inches.Height * 72);
using var ms = new MemoryStream();
using (var stream = new SKManagedWStream(ms))
using (var document = SKDocument.CreatePdf(stream, new SKDocumentPdfMetadata
{
    RasterDpi = Dpi, EncodingQuality = 85, Author = "...", Producer = "DrawnUI", Title = "...",
}))
{
    foreach (var page in pages)
    {
        viewport.ViewportOffsetY = -page.Position.Y;
        RenderOnce(wrapper, paper, scale);                 // settle the scroll off the PDF
        using (var canvas = document.BeginPage(pagePoints.Width, pagePoints.Height))
        {
            canvas.Scale(72f / Dpi);
            canvas.Clear(SKColors.White);
            canvas.ClipRect(SKRect.Create(0, 0, paper.Width, margins + page.Height)); // page ends at the split, not at the paper edge
            var ctx = new SkiaDrawingContext { Canvas = canvas, Width = paper.Width, Height = paper.Height };
            wrapper.Render(new DrawingContext(ctx, new SKRect(0, 0, paper.Width, paper.Height), scale));
        }
        document.EndPage();
    }
    document.Close();
}
await File.WriteAllBytesAsync(fullFilename, ms.ToArray());

static async Task WarmUpAsync(SkiaControl layout, float width, float height, float scale)
{
    layout.Measure(width, height, scale);
    layout.Arrange(new SKRect(0, 0, layout.MeasuredSize.Pixels.Width, layout.MeasuredSize.Pixels.Height),
        layout.MeasuredSize.Pixels.Width, layout.MeasuredSize.Pixels.Height, scale);
    var size = new SKSize(layout.MeasuredSize.Pixels.Width, layout.MeasuredSize.Pixels.Height);
 
    RenderOnce(layout, size, scale);                        // starts image loads
    var started = DateTime.UtcNow;
    if (layout is IContentReadyAware aware)
        while (!aware.ContentIsLoaded && DateTime.UtcNow - started < ContentTimeout)
            await Task.Delay(50);
 
    RenderOnce(layout, size, scale);                        // reflects loaded images
    var frames = 0;
    while (layout.NeedUpdate && frames++ < 60)             // settle, capped
    {
        await Task.Delay(16);
        RenderOnce(layout, size, scale);
    }
    layout.Arrange(new SKRect(0, 0, layout.MeasuredSize.Pixels.Width, layout.MeasuredSize.Pixels.Height),
        layout.MeasuredSize.Pixels.Width, layout.MeasuredSize.Pixels.Height, scale);
}
 
static void RenderOnce(SkiaControl layout, SKSize size, float scale)
{
    using var recorder = new SKPictureRecorder();
    var canvas = recorder.BeginRecording(new SKRect(0, 0, size.Width, size.Height));
    var ctx = new SkiaDrawingContext { Canvas = canvas, Width = size.Width, Height = size.Height };
    layout.Render(new DrawingContext(ctx, new SKRect(0, 0, size.Width, size.Height), scale));
    using var picture = recorder.EndRecording();
}

var w = (int)Math.Ceiling(content.MeasuredSize.Pixels.Width);
var h = (int)Math.Ceiling(content.MeasuredSize.Pixels.Height);
using var surface = SKSurface.Create(new SKImageInfo(w, h));
surface.Canvas.Clear(SKColors.White);
var ctx = new SkiaDrawingContext { Canvas = surface.Canvas, Surface = surface, Width = w, Height = h };
content.Render(new DrawingContext(ctx, new SKRect(0, 0, w, h), scale));
surface.Flush();
using var image = surface.Snapshot();
using var encoded = image.Encode(SKEncodedImageFormat.Jpeg, 90);