apply matrix transform while drawing text

Author: tocsoft

src/ImageSharp.Drawing/Processing/Processors/Text/DrawTextProcessor{TPixel}.cs

@@ -63,7 +63,8 @@ protected override void BeforeImageApply()
                 this.Configuration.MemoryAllocator,
                 this.Text.Length,
                 this.Pen,
-                this.Brush != null)
+                this.Brush != null,
+                this.Options.TextOptions.Transform)
             {
                 Options = this.Options
             };
@@ -185,7 +186,7 @@ private class CachingGlyphRenderer : IColorGlyphRenderer, IDisposable
             // - Provide a good accuracy (smaller than 0.2% image difference compared to the non-caching variant)
             // - Cache hit ratio above 60%
             private const float AccuracyMultiple = 8;
-
+            private readonly Matrix3x2 transform;
             private readonly PathBuilder builder;
 
             private Point currentRenderPosition;
@@ -201,7 +202,7 @@ private class CachingGlyphRenderer : IColorGlyphRenderer, IDisposable
             private readonly bool renderFill;
             private bool rasterizationRequired;
 
-            public CachingGlyphRenderer(MemoryAllocator memoryAllocator, int size, IPen pen, bool renderFill)
+            public CachingGlyphRenderer(MemoryAllocator memoryAllocator, int size, IPen pen, bool renderFill, Matrix3x2 transform)
             {
                 this.MemoryAllocator = memoryAllocator;
                 this.currentRenderPosition = default;
@@ -220,6 +221,7 @@ public CachingGlyphRenderer(MemoryAllocator memoryAllocator, int size, IPen pen,
                     this.OutlineOperations = new List<DrawingOperation>(size);
                 }
 
+                this.transform = transform;
                 this.builder = new PathBuilder();
             }
 
@@ -251,8 +253,12 @@ public void BeginFigure()
             public bool BeginGlyph(FontRectangle bounds, GlyphRendererParameters parameters)
             {
                 this.currentColor = null;
-                this.currentRenderPosition = Point.Truncate(bounds.Location);
-                PointF subPixelOffset = bounds.Location - this.currentRenderPosition;
+                var currentBounds = new RectangularPolygon(bounds.X, bounds.Y, bounds.Width, bounds.Height)
+                    .Transform(this.transform)
+                    .Bounds;
+
+                this.currentRenderPosition = Point.Truncate(currentBounds.Location);
+                PointF subPixelOffset = currentBounds.Location - this.currentRenderPosition;
 
                 subPixelOffset.X = MathF.Round(subPixelOffset.X * AccuracyMultiple) / AccuracyMultiple;
                 subPixelOffset.Y = MathF.Round(subPixelOffset.Y * AccuracyMultiple) / AccuracyMultiple;
@@ -272,7 +278,11 @@ public bool BeginGlyph(FontRectangle bounds, GlyphRendererParameters parameters)
                 this.builder.Clear();
 
                 // ensure all glyphs render around [zero, zero]  so offset negative root positions so when we draw the glyph we can offset it back
-                this.builder.SetOrigin(new PointF(-(int)bounds.X + this.offset, -(int)bounds.Y + this.offset));
+                var origionTransform = new Vector2(-(int)currentBounds.X + this.offset, -(int)currentBounds.Y + this.offset);
+
+                var transform = this.transform;
+                transform.Translation = transform.Translation + origionTransform;
+                this.builder.SetTransform(transform);
 
                 this.rasterizationRequired = true;
                 return true;
@@ -367,7 +377,7 @@ public void EndGlyph()
 
             private Buffer2D<float> Render(IPath path)
             {
-                Size size = Rectangle.Ceiling(path.Bounds).Size;
+                Size size = Rectangle.Ceiling(path.Bounds).Size * 2;
                 size = new Size(size.Width + (this.offset * 2), size.Height + (this.offset * 2));
 
                 int subpixelCount = FillRegionProcessor.MinimumSubpixelCount;

src/ImageSharp.Drawing/Processing/TextOptions.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System.Collections.Generic;
+using System.Numerics;
 using SixLabors.Fonts;
 
 namespace SixLabors.ImageSharp.Drawing.Processing
@@ -136,6 +137,11 @@ public float LineSpacing
         /// </summary>
         public bool RenderColorFonts { get; set; } = true;
 
+        /// <summary>
+        /// Gets or sets the transform to apply to the text during rendering.
+        /// </summary>
+        public Matrix3x2 Transform { get; set; } = Matrix3x2.Identity;
+
         /// <inheritdoc/>
         public TextOptions DeepClone() => new TextOptions(this);
     }

tests/ImageSharp.Drawing.Tests/Drawing/Text/DrawTextOnImageTests.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Linq;
+using System.Numerics;
 using System.Text;
 using SixLabors.Fonts;
 using SixLabors.ImageSharp.Drawing.Processing;
@@ -158,6 +159,81 @@ public void FontShapesAreRenderedCorrectly<TPixel>(
                 appendSourceFileOrDescription: true);
         }
 
+        [Theory]
+        [WithSolidFilledImages(50, 50, "White", PixelTypes.Rgba32, 50, 25, 25, "OpenSans-Regular.ttf", "i", 45, 25, 25)]
+        [WithSolidFilledImages(200, 200, "White", PixelTypes.Rgba32, 50, 100, 100, "SixLaborsSampleAB.woff", AB, 45, 100, 100)]
+        [WithSolidFilledImages(1100, 1100, "White", PixelTypes.Rgba32, 50, 550, 550, "OpenSans-Regular.ttf", TestText, 45, 550, 550)]
+        [WithSolidFilledImages(400, 400, "White", PixelTypes.Rgba32, 20, 200, 200, "OpenSans-Regular.ttf", TestText, 45, 200, 200)]
+        public void FontShapesAreRenderedCorrectly_WithRotationApplied<TPixel>(
+            TestImageProvider<TPixel> provider,
+            int fontSize,
+            int x,
+            int y,
+            string fontName,
+            string text,
+            float angle,
+            float rotationOriginX,
+            float rotationOriginY)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            Font font = CreateFont(fontName, fontSize);
+
+            var radians = (float)Math.PI * angle / 180f;
+
+            provider.RunValidatingProcessorTest(
+                c => c
+                    .SetTextOptions(o =>
+                    {
+                        o.HorizontalAlignment = HorizontalAlignment.Center;
+                        o.VerticalAlignment = VerticalAlignment.Center;
+                        o.Transform = Matrix3x2.CreateRotation(radians, new Vector2(rotationOriginX, rotationOriginY));
+                    })
+                    .DrawText(text, font, Color.Black, new PointF(x, y)),
+                $"{fontName}-{fontSize}-{ToTestOutputDisplayText(text)}-({x},{y})",
+                TextDrawingComparer,
+                appendPixelTypeToFileName: false,
+                appendSourceFileOrDescription: true);
+        }
+
+
+        [Theory]
+        [WithSolidFilledImages(50, 50, "White", PixelTypes.Rgba32, 50, 25, 25, "OpenSans-Regular.ttf", "i", -12, 0, 25, 25)]
+        [WithSolidFilledImages(200, 200, "White", PixelTypes.Rgba32, 50, 100, 100, "SixLaborsSampleAB.woff", AB, 10, 0, 100, 100)]
+        [WithSolidFilledImages(1100, 1100, "White", PixelTypes.Rgba32, 50, 550, 550, "OpenSans-Regular.ttf", TestText, 0, 10, 550, 550)]
+        [WithSolidFilledImages(400, 400, "White", PixelTypes.Rgba32, 20, 200, 200, "OpenSans-Regular.ttf", TestText, 0, -10, 200, 200)]
+        public void FontShapesAreRenderedCorrectly_WithSkewApplied<TPixel>(
+            TestImageProvider<TPixel> provider,
+            int fontSize,
+            int x,
+            int y,
+            string fontName,
+            string text,
+            float angleX,
+            float angleY,
+            float rotationOriginX,
+            float rotationOriginY)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            Font font = CreateFont(fontName, fontSize);
+
+            var radianX = (float)Math.PI * angleX / 180f;
+            var radianY = (float)Math.PI * angleY / 180f;
+
+            provider.RunValidatingProcessorTest(
+                c => c
+                    .SetTextOptions(o =>
+                    {
+                        o.HorizontalAlignment = HorizontalAlignment.Center;
+                        o.VerticalAlignment = VerticalAlignment.Center;
+                        o.Transform = Matrix3x2.CreateSkew(radianX, radianY, new Vector2(rotationOriginX, rotationOriginY));
+                    })
+                    .DrawText(text, font, Color.Black, new PointF(x, y)),
+                $"{fontName}-{fontSize}-{ToTestOutputDisplayText(text)}-({x},{y})",
+                TextDrawingComparer,
+                appendPixelTypeToFileName: false,
+                appendSourceFileOrDescription: true);
+        }
+
         /// <summary>
         /// Based on:
         /// https://github.com/SixLabors/ImageSharp/issues/572