FPSCounter

samples/SkijaInjectSample/build.gradle

@@ -53,3 +53,7 @@ dependencies {
 application {
     mainClassName = 'SkijaInjectSample.AppKt'
 }
+
+run {
+    systemProperty("skiko.fps.enabled", "true")
+}
\ No newline at end of file

skiko/src/jvmMain/kotlin/org/jetbrains/skiko/FPSCounter.kt

+package org.jetbrains.skiko
+
+import java.util.*
+import kotlin.math.roundToInt
+
+internal class FPSCounter(
+    private val count: Int,
+    private val probability: Double
+) {
+    private var i = 0
+    private val times = LinkedList<Double>()
+    private var t1 = System.nanoTime()
+
+    /**
+     * [value] 0.0 - min, 1.0 - max, 0.5 - median
+     */
+    private fun MutableList<Double>.quantile(value: Double) : Double {
+        sort()
+        val index = (value * (size - 1)).toInt()
+        return this[index]
+    }
+
+    fun tick() {
+        val t2 = System.nanoTime()
+        val frameTime = (t2 - t1) / 1E6
+        t1 = t2
+
+        i++
+        times.add(frameTime)
+
+        if (times.size > count) {
+            times.removeFirst()
+        }
+
+        if (i % count == 0) {
+            val quantile = (1 - probability) / 2.0
+            val average = (1000.0 / times.average()).roundToInt()
+            val min = (1000.0 / times.quantile(1 - quantile)).roundToInt()
+            val max = (1000.0 / times.quantile(quantile)).roundToInt()
+            val probability = (100 * probability).roundToInt()
+            println("FPS $average ($min-$max $probability%)")
+        }
+    }
+}
\ No newline at end of file

skiko/src/jvmMain/kotlin/org/jetbrains/skiko/SkiaLayer.kt

@@ -50,7 +50,16 @@ open class SkiaLayer() : HardwareLayer() {
         renderer?.onDispose()
     }
 
+    private val fpsCounter = FPSCounter(
+        count = System.getProperty("skiko.fps.count")?.toInt() ?: 500,
+        probability = System.getProperty("skiko.fps.probability")?.toDouble() ?: 0.97
+    )
+
     override fun draw() {
+        if (System.getProperty("skiko.fps.enabled") == "true") {
+            fpsCounter.tick()
+        }
+
         if (!inited) {
             if (skijaState.context == null) {
                 skijaState.context = when (api) {