Add rudimentary buffer scrolling when cursor leaves window

Squashed in fix for crash when only moving one line

sloth/common.scm

@@ -5,12 +5,16 @@
             get-main-win
             set-cursor-pos
             end
+            width
+            height
             write-buffer))
 
 (define-class <sloth-frontend> ()
-  (main-win #:getter get-main-win #:init-keyword #:main-win))
+  (main-win #:getter get-main-win #:init-keyword #:main-win)
+  (height #:accessor height)
+  (width #:accessor width))
 
 (define-generic fetch-input)            ; args: <sloth-frontend>
-(define-generic set-cursor-pos)         ; args: <sloth-frontend> x y
+(define-generic set-cursor-pos)         ; args: <sloth-frontend> x y scroll line
 (define-generic end)                    ; args: <sloth-frontend>
-(define-generic write-buffer) ; args: <sloth-frontend> buffer lines-scrolled
+(define-generic write-buffer)           ; args: <sloth-frontend> buffer scroll

sloth/editor.scm

@@ -123,9 +123,20 @@
               (if relative?
                   (+ y (cury state))
                   y)))
+  (define scroll (lines-scrolled state))
+  (define screen-height (height (get-frontend state)))
+  (define relative-y (- (cury state) scroll))
+  (if (>= relative-y
+          screen-height)
+      (set! (lines-scrolled state) (cury state)))
+  (if (< relative-y 0)
+      (set! (lines-scrolled state)
+            (max 0 (- (cury state) screen-height))))
   (set-cursor-pos (get-frontend state)
                   (curx state)
-                  (cury state)))
+                  (cury state)
+                  (lines-scrolled state)
+                  (list-ref (buffer state) (cury state))))
 
 (define (string-insert s ch k)
   (string-append

sloth/ncurses.scm

@@ -1,7 +1,8 @@
 (define-module (sloth ncurses)
   #:use-module (ncurses curses)
-  #:use-module (sloth interface)
+  #:use-module (sloth editor)
   #:use-module (sloth common)
+  #:use-module (sloth interface)
   #:use-module (oop goops)
   #:export (init-ncurses))
 
@@ -12,6 +13,11 @@
   (curx #:init-value 0 #:accessor curx)
   (cury #:init-value 0 #:accessor cury))
 
+(define-method (initialize (nc <ncurses-frontend>) . initargs)
+  (set! (height nc) (lines))
+  (set! (width nc) (cols))
+  (next-method))
+
 (define (init-ncurses)
   (define win (initscr))
   (define state (make <ncurses-frontend>
@@ -278,22 +284,26 @@
                    ((#\/) 'm-/)
                    ((#\?) 'm-?)))))))))
 
-(define-method (set-cursor-pos (nc <ncurses-frontend>) x y)
-  (set! (curx nc) x)
-  (set! (cury nc) y)
-  (move (get-main-win nc) y x))
+(define-method (set-cursor-pos (nc <ncurses-frontend>) x y scroll line)
+  (define y-real (max 0 (- y scroll)))
+  (define tabcount (string-count line #\tab))
+  (define x-real (+ (- x tabcount)
+                    (* (tabsize) tabcount)))
+  (set! (curx nc) x-real)
+  (set! (cury nc) y-real)
+  (move (get-main-win nc) y-real x-real))
 
 (define-method (end (nc <ncurses-frontend>))
   (endwin)
   (quit))
 
-(define-method (write-buffer (nc <ncurses-frontend>) buffer lines-scrolled)
+(define-method (write-buffer (nc <ncurses-frontend>) buffer scroll)
   (define win (get-main-win nc))
   (erase win)
   (do ((i 0 (1+ i)))
       ((or (> i (lines))
-           (>= (+ i lines-scrolled) (length buffer))))
-    (addstr win (list-ref buffer (+ i lines-scrolled))
+           (>= (+ i scroll) (length buffer))))
+    (addstr win (list-ref buffer (+ i scroll))
             #:y i #:x 0))
   (move win (cury nc) (curx nc))
   (refresh win))