prevent text wandering from baseline

src/ImageSharp.Drawing/Processing/Processors/Text/DrawTextProcessor.cs

@@ -97,7 +97,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Text
 
             this.textRenderer = new CachingGlyphRenderer(source.GetMemoryAllocator(), this.Text.Length, this.Pen, this.Brush != null);
             this.textRenderer.Options = (GraphicsOptions)this.Options;
-            TextRenderer.RenderTextTo(this.textRenderer, this.Text, style);
+            var renderer = new TextRenderer(this.textRenderer);
+            renderer.RenderText(this.Text, style);
         }
 
         protected override void AfterImageApply(Image<TPixel> source, Rectangle sourceRectangle)
@@ -164,14 +165,18 @@ namespace SixLabors.ImageSharp.Processing.Processors.Text
 
         private class CachingGlyphRenderer : IGlyphRenderer, IDisposable
         {
+            // just enough accuracy to allow for half pixel differences which
+            // later are componded into full pixel offsets while rendering.
+            private const float AcuracyMultiple = 2;
+
             private PathBuilder builder;
 
             private Point currentRenderPosition = default;
-            private GlyphRendererParameters currentGlyphRenderParams = default;
+            private (GlyphRendererParameters glyph, PointF subPixelOffset) currentGlyphRenderParams = default;
             private int offset = 0;
             private PointF currentPoint = default(PointF);
 
-            private readonly Dictionary<GlyphRendererParameters, GlyphRenderData> glyphData = new Dictionary<GlyphRendererParameters, GlyphRenderData>();
+            private readonly Dictionary<(GlyphRendererParameters glyph, PointF subPixelOffset), GlyphRenderData> glyphData = new Dictionary<(GlyphRendererParameters glyph, PointF subPixelOffset), GlyphRenderData>();
 
             private bool renderOutline = false;
             private bool renderFill = false;
@@ -216,11 +221,15 @@ namespace SixLabors.ImageSharp.Processing.Processors.Text
             public bool BeginGlyph(RectangleF bounds, GlyphRendererParameters paramters)
             {
                 this.currentRenderPosition = Point.Truncate(bounds.Location);
+                PointF dif = bounds.Location - this.currentRenderPosition;
+
+                dif.X = ((int)(dif.X * AcuracyMultiple)) / AcuracyMultiple;
+                dif.Y = ((int)(dif.Y * AcuracyMultiple)) / AcuracyMultiple;
 
                 // we have offset our rendering origion a little bit down to prevent edge cropping, move the draw origin up to compensate
                 this.currentRenderPosition = new Point(this.currentRenderPosition.X - this.offset, this.currentRenderPosition.Y - this.offset);
-                this.currentGlyphRenderParams = paramters;
-                if (this.glyphData.ContainsKey(paramters))
+                this.currentGlyphRenderParams = (paramters, dif);
+                if (this.glyphData.ContainsKey(this.currentGlyphRenderParams))
                 {
                     // we have already drawn the glyph vectors skip trying again
                     this.raterizationRequired = false;
@@ -252,7 +261,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Text
 
             public void Dispose()
             {
-                foreach (KeyValuePair<GlyphRendererParameters, GlyphRenderData> kv in this.glyphData)
+                foreach (KeyValuePair<(GlyphRendererParameters glyph, PointF subPixelOffset), GlyphRenderData> kv in this.glyphData)
                 {
                     kv.Value.Dispose();
                 }

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

@@ -22,8 +22,8 @@ namespace SixLabors.ImageSharp.Tests.Drawing.Text
 
         private const string TestText = "Sphinx of black quartz, judge my vow\n0123456789";
 
-        public static ImageComparer TextDrawingComparer = ImageComparer.TolerantPercentage(0.01f);
-        public static ImageComparer OutlinedTextDrawingComparer = ImageComparer.TolerantPercentage(0.5f, 3);
+        public static ImageComparer TextDrawingComparer = ImageComparer.Exact;//.TolerantPercentage(0.01f);
+        public static ImageComparer OutlinedTextDrawingComparer = ImageComparer.Exact;// TolerantPercentage(0.5f, 3);
 
         [Theory]
         [WithSolidFilledImages(200, 100, "White", PixelTypes.Rgba32, 50, 0, 0, "SixLaborsSampleAB.woff", AB)]

tests/Images/External

@@ -1 +1 @@
-Subproject commit c6980db777e49d5e526b56cb986001d1a191acdf
+Subproject commit 5634b8b2affa1158cec31ccbb67f9583e9137234