f32: add Affine2D.String

Signed-off-by: Elias Naur <mail@eliasnaur.com>

f32/affine.go

@@ -3,6 +3,7 @@
 package f32
 
 import (
+	"fmt"
 	"math"
 )
 
@@ -135,3 +136,8 @@ func (a Affine2D) shear(radiansX, radiansY float32) Affine2D {
 		(a.a+1)*ty + a.d, a.b*ty + (a.e + 1) - 1, a.f*ty + a.f,
 	}
 }
+
+func (a Affine2D) String() string {
+	sx, hx, ox, hy, sy, oy := a.Elems()
+	return fmt.Sprintf("[[%f %f %f] [%f %f %f]]", sx, hx, ox, hy, sy, oy)
+}