From 36d620108c2844bf59f3f5a5c35fe34c6edfde4a Mon Sep 17 00:00:00 2001
From: Sander Schobers <sander@schobers.eu>
Date: Thu, 4 Jul 2019 22:15:32 +0200
Subject: [PATCH] Optimized rendering a lot of labels.

- Added caching of the desired size of a label.
---
 ui/desiredsizecache.go | 21 +++++++++++++++++++++
 ui/label.go            | 14 +++++++++-----
 2 files changed, 30 insertions(+), 5 deletions(-)
 create mode 100644 ui/desiredsizecache.go

diff --git a/ui/desiredsizecache.go b/ui/desiredsizecache.go
new file mode 100644
index 0000000..314fdc7
--- /dev/null
+++ b/ui/desiredsizecache.go
@@ -0,0 +1,21 @@
+package ui
+
+import (
+	"github.com/minio/highwayhash"
+	"opslag.de/schobers/geom"
+)
+
+type desiredSizeCache struct {
+	sum  [32]byte
+	size geom.PointF32
+}
+
+func (c *desiredSizeCache) Update(ctx Context, data string, calcFn func(Context) geom.PointF32) geom.PointF32 {
+	var key = [32]byte{}
+	sum := highwayhash.Sum([]byte(data), key[:])
+	if c.sum != sum {
+		c.size = calcFn(ctx)
+		c.sum = sum
+	}
+	return c.size
+}
diff --git a/ui/label.go b/ui/label.go
index 8328fe5..96c588d 100644
--- a/ui/label.go
+++ b/ui/label.go
@@ -8,6 +8,8 @@ type Label struct {
 	ControlBase
 
 	Text string
+
+	size desiredSizeCache
 }
 
 func BuildLabel(text string, fn func(*Label)) *Label {
@@ -20,11 +22,13 @@ func BuildLabel(text string, fn func(*Label)) *Label {
 
 func (l *Label) DesiredSize(ctx Context) geom.PointF32 {
 	var fontName = l.FontName(ctx)
-	var font = ctx.Renderer().Font(fontName)
-	var width = font.WidthOf(l.Text)
-	var height = font.Height()
-	var pad = ctx.Style().Dimensions.TextPadding
-	return geom.PtF32(width+pad*2, height+pad*2)
+	return l.size.Update(ctx, fontName+l.Text, func(ctx Context) geom.PointF32 {
+		var font = ctx.Renderer().Font(fontName)
+		var width = font.WidthOf(l.Text)
+		var height = font.Height()
+		var pad = ctx.Style().Dimensions.TextPadding
+		return geom.PtF32(width+pad*2, height+pad*2)
+	})
 }
 
 func (l *Label) Render(ctx Context) {