prevent dc<%> state contamination among transparent canvases

collects/mred/private/wx/common/backing-dc.rkt

@@ -194,6 +194,7 @@
 (define (backing-draw-bm bm cr w h)
   (if (procedure? bm)
       (begin
+        (send cairo-dc reset-config)
         (send cairo-dc set-cr cr w h)
         (bm cairo-dc)
         (send cairo-dc set-cr #f 0 0))

collects/racket/draw/private/dc.rkt

@@ -322,6 +322,36 @@
 
     (define current-xform (vector 1.0 0.0 0.0 1.0 0.0 0.0))
 
+    (define/public (reset-config)
+      (start-atomic)
+      (set! matrix (make-cairo_matrix_t 1 0 0 1 0 0))
+      (set! origin-x 0.0)
+      (set! origin-y 0.0)
+      (set! scale-x 1.0)
+      (set! scale-y 1.0)
+      (set! rotation 0.0)
+      (set! effective-scale-x 1.0)
+      (set! effective-scale-y 1.0)
+      (set! effective-origin-x 0.0)
+      (set! effective-origin-y 0.0)
+      (set! current-xform (vector 1.0 0.0 0.0 1.0 0.0 0.0))
+      (set! pen (send the-pen-list find-or-create-pen "black" 1 'solid))
+      (set! brush (send the-brush-list find-or-create-brush "white" 'solid))
+      (set! font (send the-font-list find-or-create-font 12 'default))
+      (set! text-fg (send the-color-database find-color "black"))
+      (set! text-bg (send the-color-database find-color "white"))
+      (set! text-mode 'transparent)
+      (set! bg (send the-color-database find-color "white"))
+      (set! pen-stipple-s #f)
+      (set! brush-stipple-s #f)
+      (set! x-align-delta 0.5)
+      (set! y-align-delta 0.5)
+      (set! smoothing 'unsmoothed)
+      (set! current-smoothing #f)
+      (set! alpha 1.0)
+      (set! clipping-region #f)
+      (end-atomic))
+
     (define/private (reset-effective!)
       (let* ([mx (make-cairo_matrix_t 1 0 0 1 0 0)])
         (cairo_matrix_multiply mx mx matrix)

collects/racket/draw/private/local.rkt

@@ -21,6 +21,7 @@
   ;; dc%
   in-cairo-context
   get-clipping-matrix
+  reset-config
 
   ;; region%
   install-region