From cdd75000effac0216588766234cfa5b3e8e304d5 Mon Sep 17 00:00:00 2001
From: Paweł Redman <pawel.redman@gmail.com>
Date: Wed, 8 Nov 2017 12:26:43 +0100
Subject: Frametime-independent dynamics.

---
 src/common.hpp    | 15 ++++++++++-----
 src/game.cpp      |  9 +++++----
 src/interface.cpp |  4 ++--
 src/main.cpp      | 19 ++++++++++++++-----
 src/render.cpp    |  5 +++--
 5 files changed, 34 insertions(+), 18 deletions(-)

diff --git a/src/common.hpp b/src/common.hpp
index f89ae08..df14f6f 100644
--- a/src/common.hpp
+++ b/src/common.hpp
@@ -175,7 +175,7 @@ namespace game {
 	class unit_t;
 
 	class state_t {
-		double now;
+		double now, dt;
 
 		std::unordered_set<unit_t*> units;
 		std::unordered_set<unit_t*> selected_units;
@@ -185,7 +185,7 @@ namespace game {
 
 		void start(void);
 		void stop(void);
-		void tick(double now_);
+		void tick(double now_, double dt_);
 
 		// These are called by the interface.
 		void select(rectf_t rect);
@@ -213,7 +213,7 @@ namespace interface {
 
 	public:
 		state_t(sf::RenderWindow *window_, game::state_t *game);
-		void tick(void);
+		void tick(double dt);
 		void render_to(render::state_t *render);
 	};
 }
@@ -264,10 +264,10 @@ namespace render {
 		void drender_text(rectf_t rect, std::string str);
 		void drender_entity(world::entity_t *ent);
 	public:
-		double now;
+		double now, dt;
 
 		state_t(sf::RenderWindow *window_);
-		void begin_frame(double time_);
+		void begin_frame(double time_, double dt_);
 		void end_frame(void);
 		void render(game::state_t *game);
 		void render(animated_texture_t *anim, rectf_t bounds, bool mirror = false);
@@ -333,3 +333,8 @@ T bilerp(T a, T b, T c, T d, T x, T y)
 	cd = lerp(c, d, x);
 	return lerp(ab, cd, y);
 }
+
+static inline float expfade(float a, float b, float l, float dt)
+{
+	return b + (a - b) * exp(-l * dt);
+}
diff --git a/src/game.cpp b/src/game.cpp
index bfc698d..a3af9ed 100644
--- a/src/game.cpp
+++ b/src/game.cpp
@@ -73,7 +73,7 @@ public:
 		link(world);
 	}
 
-	void keep_moving(double now)
+	void keep_moving(double now, double dt)
 	{
 		float time;
 
@@ -83,7 +83,7 @@ public:
 		if (move.blocked && now < move.next_attempt)
 			return;
 
-		time = 0.15; // FIXME
+		time = dt * 10;
 
 		while (time > 0.0f) {
 			v2f_t delta, next, x_new;
@@ -241,12 +241,13 @@ void state_t::command(v2f_t x)
 		unit->start_moving(x, now);
 }
 
-void state_t::tick(double now_)
+void state_t::tick(double now_, double dt_)
 {
 	now = now_;
+	dt = dt_;
 
 	for (unit_t *unit : units)
-		unit->keep_moving(now);
+		unit->keep_moving(now, dt);
 }
 
 } //namespace game
diff --git a/src/interface.cpp b/src/interface.cpp
index 11e297e..3a6a294 100644
--- a/src/interface.cpp
+++ b/src/interface.cpp
@@ -15,7 +15,7 @@ static sf::Vector2f compute_pan(sf::RenderWindow *window, sf::Vector2f pan_ref)
 	return -(vmouse - pan_ref);
 }
 
-void state_t::tick(void)
+void state_t::tick(double dt)
 {
 	sf::Vector2u size;
 	sf::Event event;
@@ -24,7 +24,7 @@ void state_t::tick(void)
 
 	size = window->getSize();
 
-	camera.zoom = (camera.zoom + camera.target_zoom) / 2;
+	camera.zoom = expfade(camera.zoom, camera.target_zoom, 15, dt);
 
 	{
 		float view_scale;
diff --git a/src/main.cpp b/src/main.cpp
index 1059cb6..f6a2de5 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -20,6 +20,8 @@ int main()
 	render::state_t render(&window);
 	game::state_t game;
 	interface::state_t interface(&window, &game);
+	size_t frame = 0;
+	double before = NAN;
 
 	window.setVerticalSyncEnabled(false);
 
@@ -29,21 +31,28 @@ int main()
 	game.start();
 
 	while (1) {
-		double now = (nano_clock() - t0) * 1.0e-9;
+		double now = (nano_clock() - t0) * 1.0e-9, dt;
 
-		game.tick(now);
-		interface.tick();
+		if (frame)
+			dt = now - before;
+		else
+			dt = 0.01;
+
+		game.tick(now, dt);
+		interface.tick(dt);
 		if (!window.isOpen())
 			break;
 
 		window.clear();
-		render.begin_frame(now);
+		render.begin_frame(now, dt);
 		render.render(&game);
 		interface.render_to(&render);
 		render.end_frame();
+
+		before = now;
+		frame++;
 	}
 
 	game.stop();
-
 	return 0;
 }
diff --git a/src/render.cpp b/src/render.cpp
index 259d898..d1b9752 100644
--- a/src/render.cpp
+++ b/src/render.cpp
@@ -65,9 +65,10 @@ state_t::state_t(sf::RenderWindow *window_)
 	font.loadFromFile("assets/LiberationMono-Regular.ttf");
 }
 
-void state_t::begin_frame(double time_)
+void state_t::begin_frame(double now_, double dt_)
 {
-	now = time_;
+	now = now_;
+	dt = dt_;
 	window->clear();
 }
 
-- 
cgit