From 84666523e9a278ac95ca43dbaa534e8aaaf3ebd2 Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Mon, 25 Feb 2019 22:08:53 +0100
Subject: Add LUPS reporting and fix glaring oversight

The GLFW window rendering loop used to dispatch the compute shaders was
restricted to 60 FPS. I did not notice this because I never actually
measured the computed lattice updates per seconds in addition to trying
to push the GPU to its limits. Turns out the lattice sizes I commonly
use can be updated 500 times per second comfortably… Now this looks more
like the performance gains promised by GPU computation.
---
 src/glfw/window.cc           |  1 +
 src/main.cc                  | 26 +++++++++++++++++++-------
 src/shader/code/collide.glsl |  2 +-
 src/timer.cc                 |  7 +++++++
 src/timer.h                  |  3 +++
 5 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/src/glfw/window.cc b/src/glfw/window.cc
index c0074ad..77be947 100644
--- a/src/glfw/window.cc
+++ b/src/glfw/window.cc
@@ -14,6 +14,7 @@ Window::Window(const std::string& title):
 	_handle(glfwCreateWindow(_width, _height, title.c_str(), NULL, NULL)) {
 	if ( _handle != nullptr ) {
 		glfwMakeContextCurrent(_handle);
+		glfwSwapInterval(0);
 		if ( glewInit() == GLEW_OK ) {
 			_good = true;
 		}
diff --git a/src/main.cc b/src/main.cc
index 0b4df95..eeeb130 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -26,7 +26,7 @@
 constexpr GLuint nX = 512;
 constexpr GLuint nY = 128;
 
-constexpr int lups = 100; // max lattice updates per second
+constexpr double maxLUPS = 500;
 
 float getWorldHeight(int window_width, int window_height, float world_width) {
 	return world_width / window_width * window_height;
@@ -120,15 +120,11 @@ int render(bool open_boundaries) {
 		return -1;
 	}
 
-	auto last_frame = timer::now();
-
 	bool update_lattice = true;
 	bool tick           = true;
 
 	auto pause_key = window.getKeyWatcher(GLFW_KEY_SPACE);
 
-	GLuint iT = 0;
-
 	int prevMouseState = 0;
 	float prevLatticeMouseX;
 	float prevLatticeMouseY;
@@ -140,6 +136,12 @@ int render(bool open_boundaries) {
 	auto tick_buffers = { lattice_a->getBuffer(), lattice_b->getBuffer(), fluid->getBuffer() };
 	auto tock_buffers = { lattice_b->getBuffer(), lattice_a->getBuffer(), fluid->getBuffer() };
 
+	GLuint iT = 0;
+	int statLUPS = 0;
+
+	auto last_lattice_update = timer::now();
+	auto last_lups_update    = timer::now();
+
 	window.render([&](bool window_size_changed) {
 		if ( pause_key.wasClicked() ) {
 			update_lattice = !update_lattice;
@@ -151,7 +153,15 @@ int render(bool open_boundaries) {
 		}
 
 		if ( update_lattice ) {
-			if ( timer::millisecondsSince(last_frame) >= 1000/lups ) {
+			if ( timer::secondsSince(last_lups_update) >= 1.0 ) {
+				std::cout << "\rComputing about " << statLUPS << " lattice updates per second." << std::flush;
+				statLUPS = 0;
+				last_lups_update = timer::now();
+			}
+
+			if ( timer::millisecondsSince(last_lattice_update) >= 1000/maxLUPS ) {
+				statLUPS += 1;
+
 				if ( tick ) {
 					interact_shader->workOn(tick_buffers);
 					collide_shader->workOn(tick_buffers);
@@ -198,7 +208,7 @@ int render(bool open_boundaries) {
 					collide_shader->dispatch(nX, nY);
 				}
 
-				last_frame = timer::now();
+				last_lattice_update = timer::now();
 			}
 		}
 
@@ -214,6 +224,8 @@ int render(bool open_boundaries) {
 		}
 	});
 
+	std::cout << std::endl;
+
 	return 0;
 }
 
diff --git a/src/shader/code/collide.glsl b/src/shader/code/collide.glsl
index 230f02e..8755a3d 100644
--- a/src/shader/code/collide.glsl
+++ b/src/shader/code/collide.glsl
@@ -20,7 +20,7 @@ const float weight[q] = float[](
 	1./36 , 1./9., 1./36.
 );
 
-const float tau   = 0.6;
+const float tau   = 0.65;
 const float omega = 1/tau;
 
 /// Vector utilities
diff --git a/src/timer.cc b/src/timer.cc
index c46017c..162b3fe 100644
--- a/src/timer.cc
+++ b/src/timer.cc
@@ -13,4 +13,11 @@ double millisecondsSince(
 	).count();
 }
 
+double secondsSince(
+	std::chrono::time_point<std::chrono::high_resolution_clock>& pit) {
+	return std::chrono::duration_cast<std::chrono::seconds>(
+		now() - pit
+	).count();
+}
+
 }
diff --git a/src/timer.h b/src/timer.h
index aed1b61..0ce6d27 100644
--- a/src/timer.h
+++ b/src/timer.h
@@ -9,4 +9,7 @@ std::chrono::time_point<std::chrono::high_resolution_clock> now();
 double millisecondsSince(
 	std::chrono::time_point<std::chrono::high_resolution_clock>& pit);
 
+double secondsSince(
+	std::chrono::time_point<std::chrono::high_resolution_clock>& pit);
+
 }
-- 
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