From 933bcac9781e60fbac488b14adfef52661e04cc4 Mon Sep 17 00:00:00 2001
From: Paul Gardner-Stephen <paul@servalproject.org>
Date: Mon, 22 Apr 2019 00:10:26 +0930
Subject: [PATCH] fix screen scrolling bugs

---
 c64/kernal/chrout.s | 35 +++++++++++++----------------------
 1 file changed, 13 insertions(+), 22 deletions(-)

diff --git a/c64/kernal/chrout.s b/c64/kernal/chrout.s
index 58680503..280a9f76 100644
--- a/c64/kernal/chrout.s
+++ b/c64/kernal/chrout.s
@@ -234,8 +234,6 @@ scroll_screen_up:
 	;; Now scroll the whole screen up either one or two lines
 	;; based on whether the first screen line is linked or not.
 
-	jsr hide_cursor_if_visible
-	
 	;; Get pointers to start of screen + colour RAM
 	lda HIBASE
 	sta current_screen_line_ptr+1
@@ -279,7 +277,8 @@ scroll_copy_loop:
 	;; Copy last partial page
 	;; We need to copy 1000-(3*256)-line length
 	;; = 232 - line length
-	lda 232
+	lda load_or_scroll_temp_pointer+0
+	lda #232
 	sec
 	sbc load_or_scroll_temp_pointer+0
 	tax
@@ -291,6 +290,17 @@ scroll_copy_loop2:
  	iny
  	dex
  	bne scroll_copy_loop2
+
+	;; Fill in scrolled up area
+	ldx load_or_scroll_temp_pointer+0
+scroll_copy_loop3:
+	lda #$20
+	sta (current_screen_line_ptr),y
+	lda text_colour
+	sta (current_screen_line_colour_ptr),y
+	iny
+	dex
+	bne scroll_copy_loop3
 	
 	;; Shift line linkage list
 	ldy #0
@@ -304,25 +314,6 @@ link_copy:
 	;; Clear line link flag of last line
 	stx screen_line_link_table+24
 
-	;; Now erase last line
-	lda HIBASE
-	clc
-	adc #3
-	sta current_screen_line_ptr+1
-	lda #>$DBC0
-	sta current_screen_line_colour_ptr+1
-	lda #$c0
-	sta current_screen_line_ptr+0
-	sta current_screen_line_colour_ptr+0
-clear_current_physical_line:	
-	ldy #39
-*	lda #$20
-	sta (current_screen_line_ptr),y
-	lda text_colour
-	sta (current_screen_line_colour_ptr),y
-	dey
-	bpl -
-	
 	;; Restore correct line pointers
 	jsr calculate_screen_line_pointer