Added gaussian blur filter

src/PixiEditor.ChangeableDocument/Changeables/Graph/Nodes/FilterNodes/BlurNode.cs

@@ -0,0 +1,81 @@
+using System.Diagnostics;
+using Drawie.Backend.Core.Surfaces;
+using Drawie.Backend.Core.Surfaces.PaintImpl;
+using Drawie.Numerics;
+
+namespace PixiEditor.ChangeableDocument.Changeables.Graph.Nodes.FilterNodes;
+
+[NodeInfo("BlurFilter")]
+public class BlurNode : FilterNode
+{
+    public InputProperty<bool> PreserveAlpha { get; }
+    
+    public InputProperty<VecD> Radius { get; }
+    
+    public BlurNode()
+    {
+        PreserveAlpha = CreateInput("PreserveAlpha", "PRESERVE_ALPHA", true);
+        Radius = CreateInput("Radius", "RADIUS", new VecD(1, 1)).WithRules(x => x.Min(new VecD(0, 0)));
+    }
+
+    protected override ImageFilter GetImageFilter()
+    {
+        var sigma = (VecF)Radius.Value;
+        var preserveAlpha = PreserveAlpha.Value;
+
+        var xFilter = GetGaussianFilter(sigma.X, true, preserveAlpha, null, out float[] xKernel);
+        
+        // Reuse xKernel if x == y
+        var yKernel = Math.Abs(sigma.Y - sigma.X) < 0.0001f ? xKernel : null;
+        var yFilter = GetGaussianFilter(sigma.Y, false, preserveAlpha, yKernel, out _);
+
+        return (xFilter, yFilter) switch
+        {
+            (null, _) => yFilter,
+            (_, null) => xFilter,
+            (_, _) => ImageFilter.CreateCompose(yFilter, xFilter)
+        };
+    }
+
+    private static ImageFilter? GetGaussianFilter(float sigma, bool isX, bool preserveAlpha, float[]? kernel, out float[] usedKernel)
+    {
+        usedKernel = null;
+        if (sigma < 0.0001f) return null;
+        
+        kernel ??= GenerateGaussianKernel(sigma);
+        usedKernel = kernel;
+        
+        var size = isX ? new VecI(kernel.Length, 1) : new VecI(1, kernel.Length);
+        var offset = isX ? new VecI(kernel.Length / 2, 0) : new VecI(0, kernel.Length / 2);
+        
+        return ImageFilter.CreateMatrixConvolution(size, kernel, 1, 0, offset, TileMode.Repeat, !preserveAlpha);
+    }
+    
+    public static float[] GenerateGaussianKernel(float sigma)
+    {
+        int radius = (int)Math.Ceiling(3 * sigma);
+        radius = Math.Min(radius, 300);
+        int kernelSize = 2 * radius + 1;
+
+        float[] kernel = new float[kernelSize];
+        float sum = 0f;
+        float twoSigmaSquare = 2 * sigma * sigma;
+
+        for (int i = 0; i < kernelSize; i++)
+        {
+            int x = i - radius;
+            kernel[i] = (float)Math.Exp(-(x * x) / twoSigmaSquare);
+            sum += kernel[i];
+        }
+
+        // Normalize the kernel to ensure the sum of elements is 1
+        for (int i = 0; i < kernelSize; i++)
+        {
+            kernel[i] /= sum;
+        }
+
+        return kernel;
+    }
+
+    public override Node CreateCopy() => new BlurNode();
+}

src/PixiEditor/ViewModels/Document/Nodes/FilterNodes/BlurNodeViewModel.cs

@@ -0,0 +1,7 @@
+using PixiEditor.ChangeableDocument.Changeables.Graph.Nodes.FilterNodes;
+using PixiEditor.ViewModels.Nodes;
+
+namespace PixiEditor.ViewModels.Document.Nodes.FilterNodes;
+
+[NodeViewModel("BLUR_FILTER_NODE", "FILTERS", null)] // TODO: Blur Icon
+internal class BlurNodeViewModel : NodeViewModel<BlurNode>;