# HG changeset patch
# User telesto
# Date 1513892287 -3600
#      Thu Dec 21 22:38:07 2017 +0100
# Node ID 7f3e7e4c8e2e5d509081498c6e21b8f25e0cb6ca
# Parent  dede6902c4af6efbd39c35525fbb6f09b408b42d
implement CellBuffer.cell, which gives a cell for x,y. this is used several times

diff --git a/cellbuffer.go b/cellbuffer.go
--- a/cellbuffer.go
+++ b/cellbuffer.go
@@ -52,8 +52,6 @@
 		// todo: error?
 		return
 	}
-	c := &cb.cells[y*cb.w+x]
-
 	for i := 0; i < len(combc); i++ {
 		r := combc[i]
 		if runewidth.RuneWidth(r) != 0 {
@@ -63,6 +61,7 @@
 		}
 	}
 
+	c := cb.cell(x, y)
 	if c.currMain != mainc {
 		c.width = runewidth.RuneWidth(mainc)
 	}
@@ -80,7 +79,7 @@
 		// todo: error?
 		return mainc, combc, style, width
 	}
-	c := &cb.cells[(y*cb.w)+x]
+	c := cb.cell(x, y)
 	mainc, combc, style = c.currMain, c.currComb, c.currStyle
 	if width = c.width; width == 0 || mainc < ' ' {
 		width = 1
@@ -101,6 +100,11 @@
 	}
 }
 
+// always guard a call ti cell with cb.isOutside
+func (cb *CellBuffer) cell(x, y int) *cell {
+	return &cb.cells[y*cb.w+x]
+}
+
 // Dirty checks if a character at the given location needs an
 // to be refreshed on the physical display.  This returns true
 // if the cell content is different since the last time it was
@@ -110,7 +114,7 @@
 		// todo: error?
 		return false
 	}
-	c := &cb.cells[(y*cb.w)+x]
+	c := cb.cell(x, y)
 	if c.lastMain == rune(0) {
 		return true
 	}
@@ -139,7 +143,7 @@
 		// todo: error?
 		return
 	}
-	c := &cb.cells[(y*cb.w)+x]
+	c := cb.cell(x, y)
 	c.lastMain = rune(0)
 	if !dirty {
 		if c.currMain == rune(0) {
@@ -162,7 +166,7 @@
 	newc := make([]cell, w*h)
 	for y := 0; y < h && y < cb.h; y++ {
 		for x := 0; x < w && x < cb.w; x++ {
-			oc := &cb.cells[(y*cb.w)+x]
+			oc := cb.cell(x, y)
 			nc := &newc[(y*w)+x]
 			nc.currMain = oc.currMain
 			nc.currComb = oc.currComb