hide cursor when drawing, minor other fixes

c64/kernal/blink_cursor.s

@@ -0,0 +1,51 @@
+	;; We have the following variables:
+	;; cursor_blink_disable
+	;; cursor_blink_countdown
+	;; cursor_saved_character
+	;; cursor_is_visible
+	;; colour_under_cursor
+	
+blink_cursor:
+	;; Is the cursor enabled?
+	bit cursor_blink_disable
+	bne no_blink_cursor
+
+	;; Do we need to redraw things?
+	dec cursor_blink_countdown
+	bpl no_blink_cursor
+
+	;; XXX - Save character colour also!
+	
+	;; Check if cursor was visible or not, and toggle
+	lda cursor_is_visible
+	bne undraw_cursor
+draw_cursor:
+	ldy current_screen_x
+	lda (current_screen_line_ptr),y
+	sta cursor_saved_character
+	eor #$80
+	sta (current_screen_line_ptr),y
+	lda #1
+	sta cursor_is_visible
+	jmp reset_blink_timer
+
+undraw_cursor:
+	lda cursor_saved_character
+	ldy current_screen_x
+	sta (current_screen_line_ptr),y
+	lda #0
+	sta cursor_is_visible
+	;; Fall through
+reset_blink_timer:	
+	;; Rest blink counter
+	;; (Compute's Mapping the 64, p39-40)
+	lda #20
+	sta cursor_blink_countdown
+no_blink_cursor:
+
+	rts
+
+hide_cursor_if_visible:
+	bit cursor_is_visible
+	bne undraw_cursor
+	rts