png/graphics/ellipse: Add class printers

* modules/png/graphics/ellipse.scm: Add class printers.
* tests/graphics.scm ("<ellipse>: display"): New test.

modules/png/graphics/ellipse.scm

@@ -1,6 +1,7 @@
 (define-module (png graphics ellipse)
   #:use-module (oop goops)
   #:use-module (png image)
+  #:use-module (png core common)
   #:use-module (png graphics pixel)
   #:use-module (png graphics graphic)
   #:use-module (png graphics point)
@@ -29,6 +30,21 @@
    #:init-value   0
    #:getter       ellipse-height))
 
+
+(define-method (%display (ellipse <ellipse>) (port <port>))
+  (format port "#<ellipse center: ~a,~a size: ~ax~a ~a>"
+          (point-x (ellipse-center ellipse))
+          (point-y (ellipse-center ellipse))
+          (ellipse-width ellipse)
+          (ellipse-height ellipse)
+          (object-address/hex-string ellipse)))
+
+(define-method (display (ellipse <ellipse>) (port <port>))
+  (%display ellipse port))
+
+(define-method (write (ellipse <ellipse>) (port <port>))
+  (%display ellipse port))
+
 
 
 (define-method (draw! (image <png-image>) (ellipse <ellipse>))

tests/graphics.scm

@@ -235,7 +235,7 @@
          #:height   100)))))
 
 
-;; Rectangle.
+;; Multiline.
 
 (test-assert "<multiline>: display"
   (with-output-to-string
@@ -246,6 +246,18 @@
                         (make <point> #:x 30 #:y 40)
                         (make <point> #:x 50 #:y 60)))))))
 
+
+;; Ellipse.
+
+(test-assert "<ellipse>: display"
+  (with-output-to-string
+    (lambda ()
+      (display
+       (make <ellipse>
+         #:center (make <point> #:x 10 #:y 20)
+         #:width  10
+         #:height 20)))))
+
 
 (define exit-status (test-runner-fail-count (test-runner-current)))