Start work on VT LineBuf in Go

tools/vt/linebuf.go

@@ -0,0 +1,54 @@
+package vt
+
+import (
+	"fmt"
+)
+
+var _ = fmt.Print
+
+type LineBuf struct {
+	cells      []Cell
+	attrs      []LineAttrs
+	line_map   []uint
+	xnum, ynum uint
+}
+
+func NewLineBuf(xnum, ynum uint) *LineBuf {
+	lm := make([]uint, ynum, ynum)
+	var i uint
+	for i = 0; i < ynum; i++ {
+		lm[i] = i
+	}
+	return &LineBuf{
+		cells: make([]Cell, xnum*ynum, xnum*ynum), attrs: make([]LineAttrs, ynum, ynum), xnum: xnum, ynum: ynum, line_map: lm,
+	}
+}
+
+func (self *LineBuf) Line(y uint) Line {
+	idx := self.line_map[y]
+	return Line{Attrs: self.attrs[y], Cells: self.cells[idx*self.xnum : (idx+1)*self.xnum]}
+}
+
+func (self *LineBuf) AddLines(n uint) {
+	ynum := self.ynum + n
+	if uint(cap(self.line_map)) >= ynum {
+		self.line_map = self.line_map[:ynum]
+		self.attrs = self.attrs[:ynum]
+		self.cells = self.cells[:ynum*self.xnum]
+	} else {
+		const extra_capacity uint = 2
+		newattrs := make([]LineAttrs, ynum, ynum+extra_capacity)
+		copy(newattrs, self.attrs)
+		newlinemap := make([]uint, ynum, ynum+extra_capacity)
+		copy(newlinemap, self.line_map)
+		for n = self.ynum; n < ynum; n++ {
+			newlinemap[n] = n
+		}
+		newcells := make([]Cell, self.xnum*ynum, self.xnum*(ynum+extra_capacity))
+		copy(newcells, self.cells)
+		self.attrs = newattrs
+		self.line_map = newlinemap
+		self.cells = newcells
+	}
+	self.ynum = ynum
+}