refactor debug info, measure render times

internal/util/clock.go

@@ -0,0 +1,28 @@
+package util
+
+import "time"
+
+// Clock is a clock to measure elapsed time.
+// It is a shorthand for the time.Since() and time.Now() combo.
+type Clock struct {
+	t time.Time
+}
+
+// NewClock returns a new clock.
+// It also starts it.
+func NewClock() (c *Clock) {
+	return &Clock{t: time.Now()}
+}
+
+// Restart resets the start time.
+// It also returns the elapsed time.
+func (c *Clock) Restart() (t time.Duration) {
+	t = time.Since(c.t)
+	c.t = time.Now()
+	return
+}
+
+// Elapsed returns the elapsed time.
+func (c *Clock) Elapsed() time.Duration {
+	return time.Since(c.t)
+}