reordered and size-optimized some screen routines

c64/kernal/screen/cursor.s

@@ -0,0 +1,81 @@
+
+//
+// Variables used:
+// - BLNSW (cursor blink switch)
+// - BLNCT (cursor blink countdown)
+// - GDBLN (cursor saved character)
+// - BLNON (if cursor is visible)
+// - GDCOL (colour under cursor)
+// - USER  (current screen line colour pointer)
+// - PNT   (current screen line pointer)
+// - PNTR  (current screen x position)
+//
+
+
+cursor_blink:
+	// Is the cursor enabled?
+	lda BLNSW
+	bne cursor_blink_end
+
+	// Do we need to redraw things?
+	dec BLNCT
+	bpl cursor_blink_end
+
+	// Check if cursor was visible or not, and toggle
+	lda BLNON
+	bne cursor_undraw
+
+	// FALLTROUGH
+
+cursor_draw:
+	jsr calculate_screen_line_pointer // XXX make sure this is not needed and remove the call
+
+	ldy PNTR
+	lda (PNT),y
+	sta GDBLN
+	eor #$80
+	sta (PNT),y
+	// Also set cursor colour
+	lda (USER),y
+	sta GDCOL
+	lda COLOR
+	sta (USER),y
+
+	lda #1
+	sta BLNON
+
+	bne cursor_blink_timer_reset // branches always
+
+cursor_disable:
+	lda #$80
+	sta BLNSW
+
+	// FALLTHROUGH
+
+cursor_hide_if_visible:
+	lda BLNON
+	beq cursor_blink_end
+
+cursor_undraw:
+
+	lda GDBLN
+	ldy PNTR
+	sta (PNT),y
+	lda GDCOL
+	sta (USER),y
+	
+	lda #0
+	sta BLNON
+
+	// FALLTROUGH
+
+cursor_blink_timer_reset:
+
+	// Rest blink counter (Mapping the 64, p39-40)
+	lda #20
+	sta BLNCT
+
+	// FALLTROUGH
+
+cursor_blink_end:
+	rts