Major optimization for syntax highlighting

highlighter.go

@@ -121,18 +121,25 @@ func GetRules(buf *Buffer) (string, string) {
 // Match takes a buffer and returns a map specifying how it should be syntax highlighted
 // The map is from character numbers to styles, so map[3] represents the style change
 // at the third character in the buffer
-func Match(rules string, buf *Buffer) map[int]tcell.Style {
-	// rules := strings.TrimSpace(GetRules(buf))
-	str := buf.text
+// Note that this map only stores changes in styles, not each character's style
+func Match(rules string, buf *Buffer, v *View) map[int]tcell.Style {
+	start := v.topline - synLinesUp
+	end := v.topline + v.height + synLinesDown
+	if start < 0 {
+		start = 0
+	}
+	if end > len(buf.lines) {
+		end = len(buf.lines)
+	}
+	str := strings.Join(buf.lines[start:end], "\n")
+	startNum := v.cursor.loc + v.cursor.Distance(0, start)
+	toplineNum := v.cursor.loc + v.cursor.Distance(0, v.topline)
 
 	lines := strings.Split(rules, "\n")
 	m := make(map[int]tcell.Style)
 	parser := regexp.MustCompile(`color (.*?)\s+"(.*)"`)
 	for _, line := range lines {
-		if strings.TrimSpace(line) == "" ||
-			strings.TrimSpace(line)[0] == '#' ||
-			strings.HasPrefix(line, "syntax") ||
-			strings.HasPrefix(line, "header") {
+		if strings.TrimSpace(line) == "" {
 			// Ignore this line
 			continue
 		}
@@ -148,14 +155,25 @@ func Match(rules string, buf *Buffer) map[int]tcell.Style {
 		if regex.MatchString(str) {
 			indicies := regex.FindAllStringIndex(str, -1)
 			for _, value := range indicies {
+				value[0] += startNum
+				value[1] += startNum
 				for i := value[0] + 1; i < value[1]; i++ {
 					if _, exists := m[i]; exists {
 						delete(m, i)
 					}
 				}
-				m[value[0]] = st
-				if _, exists := m[value[1]]; !exists {
-					m[value[1]] = tcell.StyleDefault
+
+				if value[0] < toplineNum && value[1] > toplineNum {
+					m[toplineNum] = st
+				}
+
+				if value[0] >= toplineNum {
+					m[value[0]] = st
+				}
+				if value[1] >= toplineNum {
+					if _, exists := m[value[1]]; !exists {
+						m[value[1]] = tcell.StyleDefault
+					}
 				}
 			}
 		}

micro.go

@@ -10,7 +10,9 @@ import (
 )
 
 const (
-	tabSize = 4
+	tabSize      = 4
+	synLinesUp   = 100
+	synLinesDown = 100
 )
 
 func main() {
@@ -71,6 +73,7 @@ func main() {
 	redraw := 2
 	for {
 		if redraw == 2 {
+			v.matches = Match(v.buf.rules, v.buf, v)
 			s.Clear()
 			v.Display()
 			v.cursor.Display()

view.go

@@ -23,6 +23,9 @@ type View struct {
 
 	mouseReleased bool
 
+	// Syntax highlighting matches
+	matches map[int]tcell.Style
+
 	s tcell.Screen
 }
 
@@ -301,8 +304,6 @@ func (v *View) Display() {
 
 	charNum := v.cursor.loc + v.cursor.Distance(0, v.topline)
 
-	matches := Match(v.buf.rules, v.buf)
-
 	// Convert the length of buffer to a string, and get the length of the string
 	// We are going to have to offset by that amount
 	maxLineLength := len(strconv.Itoa(len(v.buf.lines)))
@@ -338,7 +339,7 @@ func (v *View) Display() {
 		tabchars := 0
 		for _, ch := range line {
 			var lineStyle tcell.Style
-			st, ok := matches[charNum]
+			st, ok := v.matches[charNum]
 			if ok {
 				highlightStyle = st
 			}
@@ -365,7 +366,7 @@ func (v *View) Display() {
 			x++
 		}
 		x = 0
-		st, ok := matches[charNum]
+		st, ok := v.matches[charNum]
 		if ok {
 			highlightStyle = st
 		}