SvgGradientServer.cs

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Drawing2D;
using Svg.Transforms;

namespace Svg
{
    /// <summary>
    /// Provides the base class for all paint servers that wish to render a gradient.
    /// </summary>
    public abstract class SvgGradientServer : SvgPaintServer
    {
        private SvgCoordinateUnits _gradientUnits;
        private SvgGradientSpreadMethod _spreadMethod;
        private SvgGradientServer _inheritGradient;
        private List<SvgGradientStop> _stops;

        /// <summary>
        /// Initializes a new instance of the <see cref="SvgGradientServer"/> class.
        /// </summary>
        internal SvgGradientServer()
        {
            this.GradientUnits = SvgCoordinateUnits.ObjectBoundingBox;
            this.SpreadMethod = SvgGradientSpreadMethod.Pad;
            this._stops = new List<SvgGradientStop>();
        }

        /// <summary>
        /// Called by the underlying <see cref="SvgElement"/> when an element has been added to the
        /// <see cref="Children"/> collection.
        /// </summary>
        /// <param name="child">The <see cref="SvgElement"/> that has been added.</param>
        /// <param name="index">An <see cref="int"/> representing the index where the element was added to the collection.</param>
        protected override void AddElement(SvgElement child, int index)
        {
            if (child is SvgGradientStop)
            {
                this.Stops.Add((SvgGradientStop)child);
            }

            base.AddElement(child, index);
        }

        /// <summary>
        /// Called by the underlying <see cref="SvgElement"/> when an element has been removed from the
        /// <see cref="Children"/> collection.
        /// </summary>
        /// <param name="child">The <see cref="SvgElement"/> that has been removed.</param>
        protected override void RemoveElement(SvgElement child)
        {
            if (child is SvgGradientStop)
            {
                this.Stops.Remove((SvgGradientStop)child);
            }

            base.RemoveElement(child);
        }

        /// <summary>
        /// Gets the ramp of colors to use on a gradient.
        /// </summary>
        public List<SvgGradientStop> Stops
        {
            get { return this._stops; }
        }

        /// <summary>
        /// Specifies what happens if the gradient starts or ends inside the bounds of the target rectangle.
        /// </summary>
        [SvgAttribute("spreadMethod")]
        public SvgGradientSpreadMethod SpreadMethod
        {
            get { return this._spreadMethod; }
            set { this._spreadMethod = value; }
        }

        /// <summary>
        /// Gets or sets the coordinate system of the gradient.
        /// </summary>
        [SvgAttribute("gradientUnits")]
        public SvgCoordinateUnits GradientUnits
        {
            get { return this._gradientUnits; }
            set { this._gradientUnits = value; }
        }

        /// <summary>
        /// Gets or sets another gradient fill from which to inherit the stops from.
        /// </summary>
        [SvgAttribute("href")]
        public SvgGradientServer InheritGradient
        {
            get { return this._inheritGradient; }
            set 
            { 
                this._inheritGradient = value;
                this.InheritStops();
            }
        }

        [SvgAttribute("gradientTransform")]
        public SvgTransformCollection GradientTransform
        {
            get
            {
                return (this.Attributes.GetAttribute<SvgTransformCollection>("gradientTransform"));
            }
            set
            {
                this.Attributes["gradientTransform"] = value;
            }
        }

        private Matrix EffectiveGradientTransform
        {
            get
            {
                var transform = new Matrix();

                if (GradientTransform != null)
                {
                    transform.Multiply(GradientTransform.GetMatrix());
                }
                return transform;
            }
        }

        /// <summary>
        /// Gets a <see cref="ColorBlend"/> representing the <see cref="SvgGradientServer"/>'s gradient stops.
        /// </summary>
        /// <param name="owner">The parent <see cref="SvgVisualElement"/>.</param>
        /// <param name="opacity">The opacity of the colour blend.</param>
        protected ColorBlend GetColorBlend(SvgVisualElement owner, float opacity, bool radial)
        {
            int colourBlends = this.Stops.Count;
            bool insertStart = false;
            bool insertEnd = false;

            //gradient.Transform = renderingElement.Transforms.Matrix;

            //stops should be processed in reverse order if it's a radial gradient

            // May need to increase the number of colour blends because the range *must* be from 0.0 to 1.0.
            // E.g. 0.5 - 0.8 isn't valid therefore the rest need to be calculated.

            // If the first stop doesn't start at zero
            if (this.Stops[0].Offset.Value > 0)
            {
                colourBlends++;
                
                if (radial)
                {
                    insertEnd = true;
                }
                else
                {
                    insertStart = true;
                }
            }

            // If the last stop doesn't end at 1 a stop
            float lastValue = this.Stops[this.Stops.Count - 1].Offset.Value;
            if (lastValue < 100 || lastValue < 1)
            {
                colourBlends++;
                if (radial)
                {
                    insertStart = true;
                }
                else
                {
                    insertEnd = true;
                }
            }

            ColorBlend blend = new ColorBlend(colourBlends);

            // Set positions and colour values
            int actualStops = 0;
            float mergedOpacity = 0.0f;
            float position = 0.0f;
            Color colour = Color.Black;

            for (int i = 0; i < colourBlends; i++)
            {
                var currentStop = this.Stops[radial ? this.Stops.Count - 1 - actualStops : actualStops];

                mergedOpacity = opacity * currentStop.Opacity;
                position =
                    radial
                    ? 1 - (currentStop.Offset.ToDeviceValue(owner) / owner.Bounds.Width)
                    : (currentStop.Offset.ToDeviceValue(owner) / owner.Bounds.Width);
                colour = Color.FromArgb((int)(mergedOpacity * 255), currentStop.Colour);

                actualStops++;

                // Insert this colour before itself at position 0
                if (insertStart && i == 0)
                {
                    blend.Positions[i] = 0.0f;
                    blend.Colors[i] = colour;

                    i++;
                }

                blend.Positions[i] = position;
                blend.Colors[i] = colour;

                // Insert this colour after itself at position 0
                if (insertEnd && i == colourBlends - 2)
                {
                    i++;

                    blend.Positions[i] = 1.0f;
                    blend.Colors[i] = colour;
                }
            }

            return blend;
        }

        /// <summary>
        // If this gradient contains no stops then it will search any inherited gradients for stops.
        /// </summary>
        protected virtual void InheritStops()
        {
            if (this.Stops.Count == 0 && this.InheritGradient != null)
            {
                _stops.AddRange(this.InheritGradient.Stops);
            }
        }

        protected ISvgBoundable CalculateBoundable(SvgVisualElement renderingElement)
        {
            return (this.GradientUnits == SvgCoordinateUnits.ObjectBoundingBox) ? (ISvgBoundable)renderingElement : renderingElement.OwnerDocument;
        }

        protected PointF TransformPoint(PointF originalPoint)
        {
            var newPoint = new[] { originalPoint };

            EffectiveGradientTransform.TransformPoints(newPoint);

            return newPoint[0];
        }

        protected PointF TransformVector(PointF originalVector)
        {
            var newVector = new[] { originalVector };

            EffectiveGradientTransform.TransformVectors(newVector);

            return newVector[0];
        }

        protected static double CalculateDistance(PointF first, PointF second)
        {
            return Math.Sqrt(Math.Pow(first.X - second.X, 2) + Math.Pow(first.Y - second.Y, 2));
        }

        protected static float CalculateLength(PointF vector)
        {
            return (float)Math.Sqrt(Math.Pow(vector.X, 2) + Math.Pow(vector.Y, 2));
        }

        public override SvgElement DeepCopy<T>()
        {
            var newObj = base.DeepCopy<T>() as SvgGradientServer;
            
            newObj.SpreadMethod = this.SpreadMethod;
            newObj.GradientUnits = this.GradientUnits;
            newObj.InheritGradient = this.InheritGradient;
            newObj.GradientTransform = this.GradientTransform;

            return newObj;
        }
    }
}