RedactPolygon.cs
//
// This code is part of GrapeCity Documents for PDF samples.
// Copyright (c) GrapeCity, Inc. All rights reserved.
//
using System;
using System.IO;
using System.Numerics;
using System.Linq;
using System.Drawing;
using System.Text.RegularExpressions;
using GrapeCity.Documents.Pdf;
using GrapeCity.Documents.Pdf.Annotations;
using GrapeCity.Documents.Pdf.TextMap;
using GrapeCity.Documents.Pdf.AcroForms;
using GrapeCity.Documents.Drawing;
using GrapeCity.Documents.Common;

namespace GcPdfWeb.Samples
{
    // This sample demonstrates the use of RedactAnnotation.AddPolygon() method
    // which allows to add arbitrary polygons to the redact annotation.
    // It loads the first page of the PDF generated by the BalancedColumns sample,
    // and adds redact annotations that redact out some polygons on that page.
    public class RedactPolygonQ
    {
        public int CreatePDF(Stream stream)
        {
            var doc = new GcPdfDocument();
            using (var fs = File.OpenRead(Path.Combine("Resources", "PDFs", "BalancedColumns.pdf")))
            {
                // Load the original document (we will use its first page only):
                var tdoc = new GcPdfDocument();
                tdoc.Load(fs);
                // Get the first page:
                doc.MergeWithDocument(tdoc, new MergeDocumentOptions() { PagesRange = new OutputRange(1, 1) });
                var page = doc.Pages[0];

                // Set up a layout grid:
                var grid = new
                {
                    Cols = 2,
                    Rows = 6,
                    MarginX = 72,
                    MarginY = 72,
                    Radius = 36,
                    StepX = (page.Size.Width - 72) / 2,
                    StepY = (page.Size.Height - 144) / 6,
                };
                // Insertion point for next polygon to be redacted:
                PointF startIp = new PointF(page.Size.Width / 3, grid.MarginY + grid.StepY / 2);
                PointF ip = startIp;
                int ipIdx = 0;
                // Some pastels to use as redact fill colors :
                var fills = new Color[]
                {
                    Color.FromArgb(unchecked((int)0xff70ae98)),
                    Color.FromArgb(unchecked((int)0xffecbe7a)),
                    Color.FromArgb(unchecked((int)0xffe58b88)),
                    Color.FromArgb(unchecked((int)0xff9dabdd)),
                    Color.FromArgb(unchecked((int)0xff9dabd0)),
                    Color.FromArgb(unchecked((int)0xff38908f)),
                    Color.FromArgb(unchecked((int)0xffb2ebe0)),
                    Color.FromArgb(unchecked((int)0xff5e96ae)),
                    Color.FromArgb(unchecked((int)0xffffbfa3)),
                    Color.FromArgb(unchecked((int)0xffe08963)),
                    Color.FromArgb(unchecked((int)0xff9799ba)),
                    Color.FromArgb(unchecked((int)0xffbc85a3)),
                };
                var fillColor = fills[0];
                void nextIp()
                {
                    if (++ipIdx % 2 != 0)
                    {
                        ip.X += grid.StepX;
                    }
                    else
                    {
                        ip.X = startIp.X;
                        ip.Y += grid.StepY;
                    }
                    fillColor = fills[ipIdx];
                }

                // Layout helper setup done, now add some polygons to be redacted:

                // Pentagon:
                var pts = MakePolygon(ip, grid.Radius, 5, (float)-Math.PI / 2);
                AddPolygonToRedact(page, fillColor, pts);
                nextIp();

                // Hexagon:
                pts = MakePolygon(ip, grid.Radius, 6, 0);
                // Distort the shape a bit:
                pts[0].X += 18;
                pts[3].X -= 72;
                AddPolygonToRedact(page, fillColor, pts);
                nextIp();

                // Octagon:
                pts = MakePolygon(ip, grid.Radius, 8, (float)-Math.PI / 8);
                AddPolygonToRedact(page, fillColor, pts);
                nextIp();

                // Triangle:
                pts = MakePolygon(ip, grid.Radius, 3, (float)-Math.PI / 2);
                AddPolygonToRedact(page, fillColor, pts);
                nextIp();

                // Pentagram:
                pts = MakePolygon(ip, grid.Radius, 5, (float)-Math.PI / 2);
                pts = new PointF[] { pts[0], pts[2], pts[4], pts[1], pts[3], };
                AddPolygonToRedact(page, fillColor, pts);
                nextIp();

                // Same pentagram using FillMode.Winding (the default is FillMode.Alternate):
                pts = pts.Select(p_ => new PointF(p_.X + grid.StepX, p_.Y)).ToArray();
                AddPolygonToRedact(page, fillColor, pts, FillMode.Winding);
                nextIp();

                // Set up a simple oblique projection to draw a pyramid:
                var angle = Math.PI / 6;
                float s = (float)Math.Sin(angle);
                float c = (float)Math.Cos(angle);
                Func<float, float, float, PointF> project = (x_, y_, z_) => new PointF(x_ - c * y_ * 0.5f, -(z_ - s * y_ * 0.5f));
                float hedge = grid.Radius; // 1/2 edge
                Func<Vector3, PointF> p3d = v_ => { var p_ = project(v_.X, v_.Y, v_.Z); p_.X += ip.X; p_.Y += ip.Y + hedge * 0.7f; return p_; };
                // 3d points forming a square pyramid:
                var pts3d = new Vector3[]
                {
                    new Vector3(-hedge, -hedge, 0),
                    new Vector3(hedge, -hedge, 0),
                    new Vector3(hedge, hedge, 0),
                    new Vector3(-hedge, hedge, 0),
                    new Vector3(0, 0, hedge * 2),
                };
                // Project the points to draw the pyramid:
                pts = pts3d.Select(v_ => p3d(v_)).ToArray();
                // Visible edges:
                AddPolygonToRedact(page, fillColor, new PointF[] { pts[4], pts[1], pts[2], pts[3], pts[4], pts[2] });
                // For reference, invisible edges are: pts[0]..pts[4], pts[0]..pts[1], pts[0]..pts[3]
                nextIp();

                // Parallelogram:
                float dx = 10;
                pts = MakePolygon(ip, grid.Radius, 4, (float)-Math.PI / 4);
                pts[0].X += dx;
                pts[1].X -= dx;
                pts[2].X -= dx;
                pts[3].X += dx;
                AddPolygonToRedact(page, fillColor, pts);
                nextIp();

                // Trapezoid:
                pts = MakePolygon(ip, grid.Radius, 4, (float)-Math.PI / 4);
                pts[0].X -= dx;
                pts[1].X += dx;
                pts[2].X -= dx;
                pts[3].X += dx;
                AddPolygonToRedact(page, fillColor, pts);
                nextIp();

                // Hexagram:
                pts = MakePolygon(ip, grid.Radius, 6, (float)-Math.PI / 2);
                pts = new PointF[]
                {
                    pts[0],
                    Intersect(pts[0], pts[2], pts[5], pts[1]),
                    pts[1],
                    Intersect(pts[0], pts[2], pts[1], pts[3]),
                    pts[2],
                    Intersect(pts[1], pts[3], pts[2], pts[4]),
                    pts[3],
                    Intersect(pts[2], pts[4], pts[3], pts[5]),
                    pts[4],
                    Intersect(pts[4], pts[0], pts[3], pts[5]),
                    pts[5],
                    Intersect(pts[4], pts[0], pts[5], pts[1]),
                };
                AddPolygonToRedact(page, fillColor, pts);
                nextIp();

                // Octagram:
                pts = MakePolygon(ip, grid.Radius, 8, (float)-Math.PI / 2);
                pts = new PointF[]
                {
                    pts[0],
                    Intersect(pts[0], pts[2], pts[7], pts[1]),
                    pts[1],
                    Intersect(pts[1], pts[3], pts[0], pts[2]),
                    pts[2],
                    Intersect(pts[2], pts[4], pts[1], pts[3]),
                    pts[3],
                    Intersect(pts[2], pts[4], pts[3], pts[5]),
                    pts[4],
                    Intersect(pts[3], pts[5], pts[4], pts[6]),
                    pts[5],
                    Intersect(pts[5], pts[7], pts[4], pts[6]),
                    pts[6],
                    Intersect(pts[6], pts[0], pts[5], pts[7]),
                    pts[7],
                    Intersect(pts[6], pts[0], pts[1], pts[7]),
                };
                AddPolygonToRedact(page, fillColor, pts);
                nextIp();

                // Another octagram:
                pts = MakePolygon(ip, grid.Radius, 8, (float)-Math.PI / 2);
                pts = new PointF[] { pts[0], pts[3], pts[6], pts[1], pts[4], pts[7], pts[2], pts[5] };
                AddPolygonToRedact(page, fillColor, pts);

                // Apply all redacts:
                doc.Redact();

                // Done:
                doc.Save(stream);
                return doc.Pages.Count;
            }
        }

        // Finds the intersection of two infinite lines specified by
        // points a0..a1 and b0..b1.
        private PointF Intersect(PointF a0, PointF a1, PointF b0, PointF b1)
        {
            // Math:
            // y = (x - a0.X) * qa + a0.Y
            // (x - a0.X) * qa + a0.Y = (x - b0.X) * qb + b0.Y
            // (x - a0.X) * qa - (x - b0.X) * qb = b0.Y - a0.Y
            // x = (b0.Y - a0.Y + a0.X * qa - b0.X * qb) / (qa - qb)
            var ret = PointF.Empty;
            var qa = (a1.Y - a0.Y) / (a1.X - a0.X);
            var qb = (b1.Y - b0.Y) / (b1.X - b0.X);
            // Deal with non-functions (vertical lines):
            if (!float.IsFinite(qa) || !float.IsFinite(qb))
            {
                if (float.IsFinite(qa) || a0.X == b0.X)
                    ret.X = b0.X;
                else if (float.IsFinite(qb))
                    ret.X = a0.X;
                else
                    ret.X = float.NaN;
            }
            else if (qa == qb)
                ret.X = float.NaN;
            else
                ret.X = (b0.Y - a0.Y + a0.X * qa - b0.X * qb) / (qa - qb);
            if (float.IsFinite(qa))
                ret.Y = (ret.X - a0.X) * qa + a0.Y;
            else
                ret.Y = (ret.X - b0.X) * qb + b0.Y;
            return ret;
        }

        private PointF[] MakePolygon(PointF center, float r, int n, float startAngle)
        {
            PointF[] pts = new PointF[n];
            for (int i = 0; i < n; ++i)
                pts[i] = new PointF(center.X + (float)(r * Math.Cos(startAngle + 2 * Math.PI * i / n)), center.Y + (float)(r * Math.Sin(startAngle + 2 * Math.PI * i / n)));
            return pts;
        }

        private void AddPolygonToRedact(Page p, Color fillColor, PointF[] pts, FillMode fillMode = FillMode.Alternate)
        {
            var redact = new RedactAnnotation()
            {
                Page = p,
                OverlayFillColor = fillColor
            };
            redact.AddPolygon(pts, fillMode);
            // Debug:
            // p.Graphics.DrawPolygon(pts, Color.Magenta);
        }
    }
}