From b529b7a7af1a832acb4bf65609fd6d24642eb277 Mon Sep 17 00:00:00 2001
From: JeremyStarTM <jeremystartm@staropensource.de>
Date: Fri, 26 Jul 2024 13:07:17 +0200
Subject: [PATCH] Make continuous render loop work (except V-Sync)

It works quite good now, but it is broken when V-Sync is turned on as it tries to render at the maximum FPS set and does not respect how fast the monitor renders. I first need to implement a monitor API for it to work.
---
 .../glfw/classes/GlfwManagementClass.java     | 55 +++++++++++--------
 1 file changed, 32 insertions(+), 23 deletions(-)

diff --git a/graphics/glfw/src/main/java/de/staropensource/sosengine/graphics/glfw/classes/GlfwManagementClass.java b/graphics/glfw/src/main/java/de/staropensource/sosengine/graphics/glfw/classes/GlfwManagementClass.java
index 39853559..1dcc9b57 100644
--- a/graphics/glfw/src/main/java/de/staropensource/sosengine/graphics/glfw/classes/GlfwManagementClass.java
+++ b/graphics/glfw/src/main/java/de/staropensource/sosengine/graphics/glfw/classes/GlfwManagementClass.java
@@ -22,18 +22,17 @@ package de.staropensource.sosengine.graphics.glfw.classes;
 import de.staropensource.sosengine.base.logging.LoggerInstance;
 import de.staropensource.sosengine.base.types.CodePart;
 import de.staropensource.sosengine.base.types.logging.LogIssuer;
+import de.staropensource.sosengine.base.utility.Math;
 import de.staropensource.sosengine.base.utility.Miscellaneous;
+import de.staropensource.sosengine.graphics.GraphicsSubsystemConfiguration;
 import de.staropensource.sosengine.graphics.classes.ApiManagementClass;
 import de.staropensource.sosengine.graphics.classes.Window;
 import de.staropensource.sosengine.graphics.glfw.exceptions.NotOnMainThreadException;
 import lombok.Getter;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.LinkedHashMap;
-import java.util.LinkedList;
-import java.util.OptionalDouble;
+import java.util.*;
 import java.util.concurrent.atomic.AtomicReference;
-import java.util.stream.Collectors;
 
 import static org.lwjgl.glfw.GLFW.*;
 
@@ -84,31 +83,41 @@ public abstract class GlfwManagementClass implements ApiManagementClass {
         if (!Miscellaneous.onMainThread())
             throw new NotOnMainThreadException();
 
-        long renderTime = 0L;
-        LinkedList<Long> renderTimes = new LinkedList<>();
-        AtomicReference<LinkedHashMap<@NotNull Window, @NotNull Throwable>> output = new AtomicReference<>(new LinkedHashMap<>());
+        AtomicReference<LinkedHashMap<@NotNull Window, @NotNull Throwable>> output = new AtomicReference<>(new LinkedHashMap<>());  // runRenderLoop output
+        long renderTime;                                                                                                            // Amount of time spent rendering
+        long sleepDuration;                                                                                                         // Time spent sleeping the thread
+        LinkedList<Long> splitDeltaTime = new LinkedList<>();                                                                       // Used for calculating the delta time (render time average over one second)
+        long reportDuration = System.currentTimeMillis();                                                                           // Used for determining when to report frame count and delta time
+        double deltaTime;                                                                                                           // Contains the average render time over one second (delta time)
 
-        // Run while the output linked map of runRenderLoop is empty
+        // Run while the 'output' is empty
         while (output.get().isEmpty()) {
-            while (renderTimes.size() >= 10)
-                renderTimes.removeLast();
-
-            renderTimes.add(Miscellaneous.measureExecutionTime(() -> {
+            renderTime = Miscellaneous.measureExecutionTime(() -> {
                 output.set(runRenderLoop());
                 frameCode.run();
-            }));
-            renderTime += renderTimes.getLast();
+            });
 
-            // Report
-            if (renderTime >= 1000) {
-                OptionalDouble average = renderTimes.stream().mapToDouble(a -> a).average();
-                if (average.isPresent())
-                    logger.info("Delta average: " + average.getAsDouble() + " | Frames/s: " + 1000 / average.getAsDouble());
-                else
-                    logger.error("Unable to get delta average and FPS");
+            // TODO v-sync is currently broken, monitor api needs to be implemented first
 
-                renderTimes.clear();
-                renderTime = 0L;
+            // Calculate amount of time the thread should spend sleeping
+            sleepDuration = (long) (1d / GraphicsSubsystemConfiguration.getInstance().getMaximumFramesPerSecond() * 1000d) - renderTime;
+            // Add render and sleep time to list used for calculating the delta time value
+            splitDeltaTime.add(renderTime + sleepDuration);
+
+            try {
+                //noinspection BusyWait // true, true
+                Thread.sleep(sleepDuration);
+            } catch (InterruptedException exception) {
+                logger.crash("Rendering loop got interrupted. This is unsupported behaviour.", exception);
+            }
+
+            // Calculate delta time and frame count every second
+            if (System.currentTimeMillis() >= reportDuration + 1000) {
+                deltaTime = Math.getMeanLong(splitDeltaTime);                                          // Calculate delta time
+                logger.info("Delta time average: " + deltaTime + " | Frames/s: " + 1000 / deltaTime);  // Print delta time and frame count to console
+
+                reportDuration = System.currentTimeMillis();                                           // Update 'reportDuration'
+                splitDeltaTime.clear();                                                                // Clear 'splitDeltaTime' list
             }
         }