reordered and size-optimized some screen routines

c64/kernal/screen/cursor_show.s

@@ -0,0 +1,34 @@
+
+//
+// Variables used:
+// - BLNSW (cursor blink switch)
+// - BLNON (if cursor is visible)
+// - BLNCT (cursor blink countdown)
+//
+
+cursor_show_if_enabled:
+	lda BLNSW
+	bne cursor_show_end
+	lda BLNON
+	bne cursor_show_end
+
+	// FALLTROUGH
+
+cursor_show:
+
+	// Set cursor as though it had just finished the off phase,
+	// so that the call to cursor_blink paints it
+	lda #$00
+	sta BLNCT
+	sta BLNON
+	jsr cursor_blink
+
+	// Then set the timeout to 1 frame, so that the cursor
+	// blinks under key repeat conditions, like on the original KERNAL
+	lda #$01
+	sta BLNCT
+
+	// FALLTROUGH
+
+cursor_show_end:
+	rts