Fix ascent and descent calculation in panorama

pict-lib/pict/private/pict.rkt

@@ -572,10 +572,13 @@
 
 (define (panorama p)
   (let-values ([(x1 y1 x2 y2 ay dy) (panorama-box! p)])
-    (let ([h (- y2 y1)])
-      (place-over (blank (- x2 x1) h (- h ay) dy)
-                  (- x1) (- y2 (pict-height p))
-                  p))))
+    (place-over (blank (- x2 x1)
+                       (- y2 y1)
+                       (- y2 ay)
+                       (- dy y1))
+                (- x1)
+                (- y2 (pict-height p))
+                p)))
 
 (define (clip-descent b)
   (let* ([w (pict-width b)]

pict-test/tests/pict/main.rkt

@@ -531,6 +531,11 @@
 (check-equal? (pict-width (rotate (rectangle 10 10) pi))
               (pict-width (panorama (rotate (rectangle 10 10) pi))))
 
+;; check panorama descent calculation (racket/pict#63)
+(let ()
+  (define p (panorama (pin-over (hline 40 2) 36 -4 (arrowhead 10 0))))
+  (check-equal? (pict-descent p) 0))
+
 ;;;; contract tests
 
 (test-case "dingbats-contracts"