for record-dc%', record initial configuration after each erase'

Closes PR 12460

collects/racket/draw/private/record-dc.rkt

@@ -103,6 +103,11 @@
   (class %
     (super-new)
 
+    (inherit get-origin get-scale get-rotation get-initial-matrix 
+             get-pen get-brush get-font
+             get-smoothing get-text-mode 
+             get-alpha get-clipping-region)
+
     (define record-limit +inf.0)
     (define current-size 0)
 
@@ -135,7 +140,30 @@
       (start-atomic)
       (set! procs null)
       (set! current-size 0)
-      (end-atomic))
+      (end-atomic)
+      ;; install current configuration explicitly (so it gets recorded):
+      (let-values ([(ox oy) (get-origin)]
+                   [(sx sy) (get-scale)]
+                   [(r) (get-rotation)]
+                   [(m) (get-initial-matrix)]
+                   [(p) (get-pen)]
+                   [(b) (get-brush)]
+                   [(s) (get-smoothing)]
+                   [(f) (get-font)]
+                   [(tm) (get-text-mode)]
+                   [(a) (get-alpha)]
+                   [(cr) (get-clipping-region)])
+        (unless (and (zero? ox) (zero? oy)) (set-origin ox oy))
+        (unless (and (= 1 sx) (= 1 sy)) (set-scale sx sy))
+        (unless (zero? r) (set-rotation r))
+        (unless (equal? m '#(1.0 0.0 0.0 1.0 0.0 0.0)) (set-initial-matrix m))
+        (do-set-pen! p)
+        (do-set-brush! b)
+        (set-font f)
+        (unless (eq? s 'unsmoothed) (set-smoothing s))
+        (unless (eq? tm 'transparent) (set-text-mode tm))
+        (unless (= a 1.0) (set-alpha a))
+        (when cr (set-clipping-region cr))))
 
     (define clones (make-hasheq))
     (define/private (clone clone-x x)

collects/tests/gracket/record-dc.rkt

@@ -0,0 +1,59 @@
+#lang racket/base
+(require racket/class
+         racket/draw
+         racket/draw/private/record-dc)
+
+(define bm1 (make-bitmap 100 100))
+(define bm2 (make-bitmap 100 100))
+(define bm3 (make-bitmap 100 100))
+
+(define dc1 (make-object bitmap-dc% bm1))
+(define dc2 (make-object (record-dc-mixin bitmap-dc%) bm2))
+(define dc3 (make-object bitmap-dc% bm3))
+
+(define (config dc)
+  (send dc set-origin 2 3)
+  (send dc set-scale 1.1 0.9)
+  (send dc set-rotation 0.1)
+  (send dc set-initial-matrix '#(1.0 -0.1 0.1 1.0 1.0 2.0))
+  (send dc set-pen "red" 2 'solid)
+  (send dc set-brush "blue" 'solid)
+  (send dc set-font (make-font #:size 32))
+  (send dc set-smoothing 'smoothed)
+  (send dc set-text-mode 'solid)
+  (send dc set-alpha 0.8)
+  (send dc set-clipping-rect 5 5 95 95))
+
+(define (draw dc)
+  (send dc draw-ellipse 2 2 100 100)
+  (send dc draw-text "Hello" 10 10))
+
+(define (get-bytes bm)
+  (define w (send bm get-width))
+  (define h (send bm get-height))
+  (define bstr (make-bytes (* 4 w h)))
+  (send bm get-argb-pixels 0 0 w h bstr)
+  bstr)
+
+(config dc1)
+(draw dc1)
+
+(define pre-bytes (get-bytes bm1))
+
+(config dc2)
+(send dc2 erase)
+(draw dc2)
+
+(define middle-bytes (get-bytes bm2))
+
+(define cms (send dc2 get-recorded-command))
+
+(cms dc3)
+
+(define post-bytes (get-bytes bm3))
+
+(unless (equal? pre-bytes middle-bytes)
+  (error "middle != pre"))
+
+(unless (equal? pre-bytes post-bytes)
+  (error "post != pre"))