diff --git a/.gitignore b/.gitignore
index 9491a2f..1269ce5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -360,4 +360,8 @@ MigrationBackup/
 .ionide/
 
 # Fody - auto-generated XML schema
-FodyWeavers.xsd
\ No newline at end of file
+FodyWeavers.xsd
+
+
+*.o
+*.exe
diff --git a/Input.h b/Input.h
new file mode 100644
index 0000000..638835c
--- /dev/null
+++ b/Input.h
@@ -0,0 +1,40 @@
+#pragma once
+
+#include <stdint.h>
+#include <stdbool.h>
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+// Types of input the player might want
+typedef enum {
+	input_Key_Left,
+	input_Key_Right,
+	input_Key_Up,
+	input_Key_Down,
+	input_Key_Jump,
+	input_Key_Attack,
+	input_Key_Spell,
+	input_Key_Use,
+	input_Key_Count
+} input_Key;
+
+// States a key might in
+typedef enum {
+	Pressed,
+	JustPressed,
+	Released,
+	JustReleased
+} input_KeyState;
+
+typedef struct {
+	input_KeyState keys[input_Key_Count]; // States of keys
+} System_Input;
+
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/Physics_Component.c b/Physics_Component.c
index deb6a6f..8d876bc 100644
--- a/Physics_Component.c
+++ b/Physics_Component.c
@@ -60,7 +60,7 @@ void _physics_MoveX(System_Physics *sys, Entity *e, Duration deltaTime);
 void _physics_MoveY(System_Physics *sys, Entity *e, Duration deltaTime);
 
 
-inline void _physics_AdvanceEntity(System_Physics *sys, Entity *e, Duration deltaTime) {
+static inline void _physics_AdvanceEntity(System_Physics *sys, Entity *e, Duration deltaTime) {
 	ASSERT(e->position && "_physics_AdvanceEntity() called on entity with no position");
 
 	// Short path
diff --git a/Physics_Component.h b/Physics_Component.h
index f197ff1..b06356a 100644
--- a/Physics_Component.h
+++ b/Physics_Component.h
@@ -16,6 +16,9 @@ typedef struct _Entity Entity;
 extern double physics_Gravity;
 
 
+// Position component.
+//
+// If not exist, it's like it's at (0,0)
 typedef struct {
 	Entity *super;
 	Vec2    position;
@@ -23,6 +26,9 @@ typedef struct {
 } Component_Position;
 
 
+// Handler called when hitboxes are hit
+typedef void (*physics_HitHandler)(Entity *me, Entity *other, Vec2 triedDelta);
+
 // Box is relative to Position if exists
 // if not, Box is absolute
 //
@@ -31,6 +37,8 @@ typedef struct {
 	Entity *super;
 	Box2    box;
 	bool    fixed;
+
+	physics_HitHandler onHit;
 } Component_Hitbox;
 
 // Returns the absolute version of the hitbox.
diff --git a/Physics_Move.c b/Physics_Move.c
index 9f3c1a1..46b60ed 100644
--- a/Physics_Move.c
+++ b/Physics_Move.c
@@ -13,6 +13,11 @@ static inline double dabs(double x) {
 	return x < 0 ? -x : x;
 }
 
+static inline void call_hithandler(Entity *me, Entity *other, Vec2 triedDelta) {
+	if (me->hitbox->onHit)
+		me->hitbox->onHit(me, other, triedDelta);
+}
+
 
 void _physics_MoveX(System_Physics *sys, Entity *e, Duration deltaTime) {
 	double delta = e->position->velocity.x * duration_Seconds(deltaTime);
@@ -29,6 +34,7 @@ void _physics_MoveX(System_Physics *sys, Entity *e, Duration deltaTime) {
 			continue;
 
 		if (box2_Intersects(tohit, box2_OffsetX(mybox, delta), NULL)) {
+			call_hithandler(e, tohit_comp->super, vec2(delta, 0));
 			if (delta > 0) {
 				// Moves right, hits left edge
 				double maxdelta = tohit.lefttop.x - mybox.lefttop.x - mybox.size.x;
@@ -63,6 +69,7 @@ void _physics_MoveY(System_Physics *sys, Entity *e, Duration deltaTime) {
 			continue;
 
 		if (box2_Intersects(tohit, box2_OffsetY(mybox, delta), NULL)) {
+			call_hithandler(e, tohit_comp->super, vec2(0, delta));
 			if (delta > 0) {
 				// Moves down, hits top edge
 				double maxdelta = tohit.lefttop.y - mybox.lefttop.y - mybox.size.y;
diff --git a/Player_Component.h b/Player_Component.h
new file mode 100644
index 0000000..90dbcfb
--- /dev/null
+++ b/Player_Component.h
@@ -0,0 +1,35 @@
+#pragma once
+
+#include <stdint.h>
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct _Entity Entity;
+
+
+// Player controller component.
+// Only one entity should have this.
+typedef struct {
+	Entity *super;
+	int     jumpCount;        // Number of times the player has jumped since leaving ground
+							  // (Initial jump does not count)
+	bool onGround;            // If the player is on the ground?
+	bool moveLeft, moveRight; // If the player is moving left/right?
+} Component_Player;
+
+
+// Player controller instance.
+// Reads input from the app.
+typedef struct {
+	// The player in the world.
+	// Control is paused if equals NULL.
+	Component_Player *player;
+} System_Player;
+
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/Types.c b/Types.c
index f6d19d8..0bd9f86 100644
--- a/Types.c
+++ b/Types.c
@@ -68,3 +68,11 @@ Box2 box2_OffsetY(Box2 box, double offsetY) {
 	box.lefttop.y += offsetY;
 	return box;
 }
+
+
+Duration duration_Now() {
+	// TODO Use Windows.h
+	// Reference: https://github.com/SFML/SFML/blob/2.6.x/src/SFML/System/Win32/ClockImpl.cpp
+	Duration d = {.microseconds = 0};
+	return d;
+}
diff --git a/Types.h b/Types.h
index 8c11316..8b4f7ab 100644
--- a/Types.h
+++ b/Types.h
@@ -14,6 +14,11 @@ typedef struct {
 } Vec2;
 
 
+inline Vec2 vec2(double x, double y) {
+	Vec2 v = {.x = x, .y = y};
+	return v;
+}
+
 Vec2 vec2_Add(Vec2 x, Vec2 y);
 Vec2 vec2_Scale(Vec2 v, double scale);
 
@@ -33,6 +38,7 @@ Box2 box2_OffsetX(Box2 box, double offsetX);
 Box2 box2_OffsetY(Box2 box, double offsetY);
 
 
+// Time duration.
 typedef struct {
 	uint64_t microseconds;
 } Duration;
@@ -40,6 +46,12 @@ typedef struct {
 static inline double duration_Seconds(const Duration t) { return ((double)t.microseconds) / 1000.0 / 1000.0; }
 static inline double duration_Milliseconds(const Duration t) { return ((double)t.microseconds) / 1000.0; }
 
+// Returns a relative duration since
+// a static time point in the past.
+//
+// Its absolute value has no meaning.
+Duration duration_Now();
+
 
 #ifdef __cplusplus
 }