Shearing support from Mike T.

src/main/java/pythagoras/f/AbstractTransform.java

@@ -97,6 +97,23 @@ public abstract class AbstractTransform implements Transform
         throw new UnsupportedOperationException();
     }
 
+    @Override // from Transform
+    public Transform shear (float sx, float sy) {
+        shearX(sx);
+        shearY(sy);
+        return this;
+    }
+
+    @Override // from Transform
+    public Transform shearX (float sx) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override // from Transform
+    public Transform shearY (float sy) {
+        throw new UnsupportedOperationException();
+    }
+
     @Override // from Transform
     public Transform setTx (float tx) {
         throw new UnsupportedOperationException();

src/main/java/pythagoras/f/AffineTransform.java

@@ -225,6 +225,21 @@ public class AffineTransform extends AbstractTransform
         return Transforms.multiply(this, 1, 0, 0, 1, 0, ty, this);
     }
 
+    @Override // from Transform
+    public Transform shear (float sx, float sy) {
+        return Transforms.multiply(this, 1, sy, sx, 1, 0, 0, this);
+    }
+
+    @Override // from Transform
+    public Transform shearX (float sx) {
+        return Transforms.multiply(this, 1, 0, sx, 1, 0, 0, this);
+    }
+
+    @Override // from Transform
+    public Transform shearY (float sy) {
+        return Transforms.multiply(this, 1, sy, 0, 1, 0, 0, this);
+    }
+
     @Override // from Transform
     public Transform invert () {
         // compute the determinant, storing the subdeterminants for later use

src/main/java/pythagoras/f/Transform.java

@@ -137,6 +137,21 @@ public interface Transform
      * @throws UnsupportedOperationException if the transform is not rigid body or greater. */
     Transform translateY (float ty);
 
+    /** Shears this transform.
+     * @return this instance, for chaining.
+     * @throws UnsupportedOperationException if the transform is not affine or greater. */
+    Transform shear (float tx, float ty);
+
+    /** Shears this transform in the x dimension.
+     * @return this instance, for chaining.
+     * @throws UnsupportedOperationException if the transform is not affine or greater. */
+    Transform shearX (float tx);
+
+    /** Shears this transform in the y dimension.
+     * @return this instance, for chaining.
+     * @throws UnsupportedOperationException if the transform is not affine or greater. */
+    Transform shearY (float ty);
+
     /** Returns a new transform that represents the inverse of this transform.
      * @throws NoninvertibleTransformException if the transform is not invertible. */
     Transform invert ();