Explicitly throw for degenerate matrices.

src/ImageSharp/Processing/Processors/Transforms/Linear/AffineTransformProcessor.cs

@@ -21,6 +21,11 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
             Guard.NotNull(sampler, nameof(sampler));
             Guard.MustBeValueType(sampler, nameof(sampler));
 
+            if (TransformUtils.IsDegenerate(matrix))
+            {
+                throw new DegenerateTransformException("Matrix is degenerate. Check input values.");
+            }
+
             this.Sampler = sampler;
             this.TransformMatrix = matrix;
             this.DestinationSize = targetDimensions;

src/ImageSharp/Processing/Processors/Transforms/Linear/AffineTransformProcessor{TPixel}.cs

@@ -61,7 +61,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
             Matrix3x2 matrix = this.transformMatrix;
 
             // Handle transforms that result in output identical to the original.
-            if (matrix.Equals(default) || matrix.Equals(Matrix3x2.Identity))
+            // Degenerate matrices are already handled in the upstream definition.
+            if (matrix.Equals(Matrix3x2.Identity))
             {
                 // The clone will be blank here copy all the pixel data over
                 var interest = Rectangle.Intersect(this.SourceRectangle, destination.Bounds());

src/ImageSharp/Processing/Processors/Transforms/Linear/ProjectiveTransformProcessor.cs

@@ -21,6 +21,11 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
             Guard.NotNull(sampler, nameof(sampler));
             Guard.MustBeValueType(sampler, nameof(sampler));
 
+            if (TransformUtils.IsDegenerate(matrix))
+            {
+                throw new DegenerateTransformException("Matrix is degenerate. Check input values.");
+            }
+
             this.Sampler = sampler;
             this.TransformMatrix = matrix;
             this.DestinationSize = targetDimensions;

src/ImageSharp/Processing/Processors/Transforms/Linear/ProjectiveTransformProcessor{TPixel}.cs

@@ -60,7 +60,8 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
             Matrix4x4 matrix = this.transformMatrix;
 
             // Handle transforms that result in output identical to the original.
-            if (matrix.Equals(default) || matrix.Equals(Matrix4x4.Identity))
+            // Degenerate matrices are already handled in the upstream definition.
+            if (matrix.Equals(Matrix4x4.Identity))
             {
                 // The clone will be blank here copy all the pixel data over
                 var interest = Rectangle.Intersect(this.SourceRectangle, destination.Bounds());