//// This code is part of Document Solutions for PDF .NET demos.// Copyright (c) MESCIUS inc. All rights reserved.//using System;using System.IO;using System.Drawing;using System.Numerics;using GrapeCity.Documents.Pdf;using GCTEXT = GrapeCity.Documents.Text;using GCDRAW = GrapeCity.Documents.Drawing;
namespace DsPdfWeb.Demos{    // This sample shows how to add a simple text watermark-like overlay    // to all pages of an existing PDF.    public class AddWatermark    {        public int CreatePDF(Stream stream)        {            var doc = new GcPdfDocument();            using var fs = File.OpenRead(Path.Combine("Resources", "PDFs", "SlidePages.pdf"));            doc.Load(fs);            foreach (var page in doc.Pages)            {                var g = page.Graphics;
                // Text layout used to draw the 'watermark':                var tl = g.CreateTextLayout();                tl.Append("DsPdf Demo");                tl.DefaultFormat.Font = GCTEXT.Font.FromFile(Path.Combine("Resources", "Fonts", "NotoSans-Bold.ttf"));                tl.DefaultFormat.FontSize = g.Resolution;                // Semi-transparent color:                tl.DefaultFormat.ForeColor = Color.FromArgb(128, Color.Yellow);                tl.DefaultFormat.GlyphAdvanceFactor = 1.5f;                tl.PerformLayout();
                // Rotation angle (radians) - from left/bottom to right/top corners of the page:                var angle = -Math.Asin(g.CanvasSize.Width / g.CanvasSize.Height);                // Page center:                var center = new PointF(g.CanvasSize.Width / 2, g.CanvasSize.Height / 2);                // Additional offset from text size:                var delta = new PointF(                    (float)((tl.ContentWidth * Math.Cos(angle) - tl.ContentHeight * Math.Sin(angle)) / 2),                    (float)((tl.ContentWidth * Math.Sin(angle) + tl.ContentHeight * Math.Cos(angle)) / 2));
                // Draw watermark text diagonally in the center of the page                // (matrix transforms are applied from last to first):                g.Transform =                    Matrix3x2.CreateRotation((float)angle) *                    Matrix3x2.CreateTranslation(center.X - delta.X, center.Y - delta.Y);
                g.DrawTextLayout(tl, PointF.Empty);                g.Transform = Matrix3x2.Identity;            }            doc.Save(stream);            return doc.Pages.Count;        }    }}