Optimise SetContent

* Remove reflect.DeepEqual call in SetContent
  > There's no need for reflection as we know the types.
  > Given tcell wants to stay compatible with older go versions, we now have
  > a small function that handles this, instead of using something like
  > `slices.Equal`.
* Add Simple benchmark to compare against the old versions
* Reuse `currComb` and `lastComb` slices to prevent allocations

cell.go

@@ -16,7 +16,6 @@ package tcell
 
 import (
 	"os"
-	"reflect"
 
 	runewidth "github.com/mattn/go-runewidth"
 )
@@ -44,6 +43,21 @@ type CellBuffer struct {
 	cells []cell
 }
 
+// we purposefully don't use slices.Equal in order to stay compatible
+// with earlier go versions.
+func runeSliceEqual(a, b []rune) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+
+	return true
+}
+
 // SetContent sets the contents (primary rune, combining runes,
 // and style) for a cell at a given location.  If the background or
 // foreground of the style is set to ColorNone, then the respective
@@ -58,13 +72,14 @@ func (cb *CellBuffer) SetContent(x int, y int,
 		// dirty as well as the base cell, to make sure we consider
 		// both cells as dirty together.  We only need to do this
 		// if we're changing content
-		if (c.width > 0) && (mainc != c.currMain || len(combc) != len(c.currComb) || (len(combc) > 0 && !reflect.DeepEqual(combc, c.currComb))) {
+		if (c.width > 0) && (mainc != c.currMain || !runeSliceEqual(combc, c.currComb)) {
 			for i := 0; i < c.width; i++ {
 				cb.SetDirty(x+i, y, true)
 			}
 		}
 
-		c.currComb = append([]rune{}, combc...)
+		// Reuse slice to prevent allocations
+		c.currComb = append(c.currComb[:0], combc...)
 
 		if c.currMain != mainc {
 			c.width = runewidth.RuneWidth(mainc)
@@ -155,7 +170,7 @@ func (cb *CellBuffer) SetDirty(x, y int, dirty bool) {
 				c.currMain = ' '
 			}
 			c.lastMain = c.currMain
-			c.lastComb = c.currComb
+			c.lastComb = append(c.lastComb[:0], c.currComb...)
 			c.lastStyle = c.currStyle
 		}
 	}

cell_test.go

@@ -0,0 +1,80 @@
+package tcell
+
+import (
+	"reflect"
+	"testing"
+
+	runewidth "github.com/mattn/go-runewidth"
+)
+
+// SetContent sets the contents (primary rune, combining runes,
+// and style) for a cell at a given location.  If the background or
+// foreground of the style is set to ColorNone, then the respective
+// color is left un changed.
+func (cb *CellBuffer) SetContentOld(x int, y int,
+	mainc rune, combc []rune, style Style,
+) {
+	if x >= 0 && y >= 0 && x < cb.w && y < cb.h {
+		c := &cb.cells[(y*cb.w)+x]
+
+		// Wide characters: we want to mark the "wide" cells
+		// dirty as well as the base cell, to make sure we consider
+		// both cells as dirty together.  We only need to do this
+		// if we're changing content
+		if (c.width > 0) && (mainc != c.currMain || len(combc) != len(c.currComb) || (len(combc) > 0 && !reflect.DeepEqual(combc, c.currComb))) {
+			for i := 0; i < c.width; i++ {
+				cb.SetDirty(x+i, y, true)
+			}
+		}
+
+		c.currComb = append([]rune{}, combc...)
+
+		if c.currMain != mainc {
+			c.width = runewidth.RuneWidth(mainc)
+		}
+		c.currMain = mainc
+		if style.fg == ColorNone {
+			style.fg = c.currStyle.fg
+		}
+		if style.bg == ColorNone {
+			style.bg = c.currStyle.bg
+		}
+		c.currStyle = style
+	}
+}
+
+func Benchmark_SetContentOld(b *testing.B) {
+	buffer := &CellBuffer{}
+	buffer.Resize(100, 100)
+	flag := []rune("🇦🇺")
+	for i := 0; i < b.N; i++ {
+		for w := 0; w < 100; w++ {
+			for h := 0; h < 100; h++ {
+				buffer.SetContentOld(w, h, 'a', nil, StyleDefault)
+			}
+		}
+		for w := 0; w < 100; w++ {
+			for h := 0; h < 100; h++ {
+				buffer.SetContentOld(w, h, flag[0], flag[1:], StyleDefault)
+			}
+		}
+	}
+}
+
+func Benchmark_SetContent(b *testing.B) {
+	buffer := &CellBuffer{}
+	buffer.Resize(100, 100)
+	flag := []rune("🇦🇺")
+	for i := 0; i < b.N; i++ {
+		for w := 0; w < 100; w++ {
+			for h := 0; h < 100; h++ {
+				buffer.SetContent(w, h, 'a', nil, StyleDefault)
+			}
+		}
+		for w := 0; w < 100; w++ {
+			for h := 0; h < 100; h++ {
+				buffer.SetContent(w, h, flag[0], flag[1:], StyleDefault)
+			}
+		}
+	}
+}