ui: More precise clock

internal/ui/ui_glfw.go

@@ -23,6 +23,10 @@ import (
 	"time"
 )
 
+func Now() int64 {
+	return time.Now().UnixNano()
+}
+
 var currentUI *userInterface
 
 func Init() {

internal/ui/ui_js.go

@@ -19,8 +19,14 @@ package ui
 import (
 	"github.com/gopherjs/gopherjs/js"
 	"strconv"
+	"time"
 )
 
+func Now() int64 {
+	// time.Now() is not reliable until GopherJS suports performance.now().
+	return int64(js.Global.Get("performance").Call("now").Float() * float64(time.Millisecond))
+}
+
 func ExecOnUIThread(f func()) {
 	f()
 }

run.go

@@ -60,7 +60,7 @@ func Run(f func(*Image) error, width, height, scale int, title string) error {
 	}
 
 	frames := 0
-	t := time.Now().UnixNano()
+	t := ui.Now()
 	for {
 		if 0 < runContext.newScreenWidth || 0 < runContext.newScreenHeight || 0 < runContext.newScreenScale {
 			changed := false
@@ -110,7 +110,7 @@ func Run(f func(*Image) error, width, height, scale int, title string) error {
 		}
 
 		// Calc the current FPS.
-		now := time.Now().UnixNano()
+		now := ui.Now()
 		frames++
 		if time.Second <= time.Duration(now-t) {
 			runContext.fps = float64(frames) * float64(time.Second) / float64(now-t)