1

🏗️

The Player Class

Position, velocity and shape in one tidy object

Active

🎯

Goal for this step

Structure the player as a class with its own update method.

1New platformer.cpp, 800×480. The Player class owns: shape, vx, vy, onGround.
2Its update(float dt) method will run all physics; main() just calls it, clean separation.
3Gravity in dt units: vy += 1400 * dt (px/sec²), position += velocity × dt.
4Construct at (100, 380), draw orange.

platformer.cpp

class Player {
public:
    sf::RectangleShape shape;
    float vx = 0, vy = 0;
    bool onGround = false;

    Player() {
        shape.setSize(sf::Vector2f(34, 44));
        shape.setPosition(100, 380);
        shape.setFillColor(sf::Color(255, 119, 0));
    }

    void update(float dt) {
        vy += 1400.f * dt;              // gravity
        shape.move(vx * dt, vy * dt);
    }
};

✏️

Fill in the Blanks

+15 XP

Gravity is now an acceleration of 1400 px/² applied via dt. The Player class keeps physics inside its own method.

🧠

Knowledge Check

+15 XP

main() calling player.update(dt) instead of doing physics itself gives you…

AFaster compilation

BA main loop you can read at a glance, and physics you can change in ONE place

CSmaller executables

2

⌨️

Running & Air Control

Target-speed movement that feels crisp

Locked

🎯

Goal for this step

Move with the arrows using target velocities, including mid-air.

1Each frame set a target vx: −260, +260 or 0 from the held arrows.
2Instant velocity (vx = target) feels crisp; optionally blend toward it for weight: vx += (target - vx) * 12 * dt.
3Keep air control at 100% for now, floaty platformers reduce it.
4Clamp x to the window.

platformer.cpp

// inside Player::update, before gravity:
float target = 0;
if (sf::Keyboard::isKeyPressed(sf::Keyboard::Left))  target = -260;
if (sf::Keyboard::isKeyPressed(sf::Keyboard::Right)) target =  260;
vx += (target - vx) * 12.f * dt;   // smooth toward target

⌨️

Code Challenge

+20 XP

Smooth the run speed toward its target:

platformer.cppp

vx += (target - ) * 12.f * ;

💡 Hint: Move a fraction of the gap between current and target each frame, scaled by delta time.

🧠

Knowledge Check

+15 XP

The line vx += (target - vx) * 12 * dt creates…

AInstant stops

BSmooth acceleration and deceleration, the gap shrinks a proportion every frame, like easing

CRandom drift

3

🦘

Jumping with Coyote Time

The secret trick every good platformer hides

Locked

🎯

Goal for this step

Add jumping plus the "coyote time" forgiveness window.

1Jump on Space (KeyPressed event): vy = -560 if allowed.
2Coyote time: keep a timer of how long since you were last grounded; allow jumps within 0.1 s of leaving a ledge.
3Players constantly press jump a few pixels AFTER running off a ledge, without forgiveness it "eats" their input and feels unfair.
4Track it: sinceGround += dt each frame, reset to 0 when landing; jump while < 0.1.

platformer.cpp

float sinceGround = 999;

// in update:
sinceGround += dt;
if (onGround) sinceGround = 0;

// jump (in the event handler):
if (event.key.code == sf::Keyboard::Space
        && player.sinceGround < 0.1f) {
    player.vy = -560;
    player.sinceGround = 999;   // spend the jump
}

💡

Celeste, Hollow Knight, Mario, all use coyote time. Roughly 0.08-0.12 s. Players never notice it; they only notice its absence.

✏️

Fill in the Blanks

+15 XP

Coyote time allows a jump within seconds of leaving the ground. After jumping we set the timer to 999 so the jump cannot be twice.

🧠

Knowledge Check

+15 XP

Why do players love coyote time without knowing it exists?

AIt makes jumps higher

BIt forgives tiny timing errors, so the game matches what players INTENDED rather than what they exactly did

CIt speeds the game up

4

🧱

Platforms & Landing

AABB landing checks against a vector of platforms

Locked

🎯

Goal for this step

Land on platforms with the falling-only rule, in clean C++.

1Platforms: std::vector<sf::FloatRect>, ground plus ledges.
2After moving: for each platform, if bounds intersect AND vy > 0 AND we came from above → snap on top, vy = 0, onGround = true.
3"Came from above": previous bottom (bottom − vy·dt) was at or above the platform top.
4Draw them from the same rects with one reusable RectangleShape.

platformer.cpp

std::vector<sf::FloatRect> platforms = {
    {0, 440, 800, 40}, {150, 340, 140, 16},
    {380, 260, 140, 16}, {610, 180, 140, 16},
};

onGround = false;
sf::FloatRect pb = shape.getGlobalBounds();
for (auto& plat : platforms) {
    if (pb.intersects(plat) && vy > 0
            && pb.top + pb.height - vy * dt <= plat.top + 1) {
        shape.setPosition(pb.left, plat.top - pb.height);
        vy = 0;
        onGround = true;
    }
}

⌨️

Code Challenge

+20 XP

Snap onto the platform you landed on:

platformer.cpp

shape.setPosition(pb.left, plat.top - pb.);
vy = ;
onGround = ;

💡 Hint: Standing on top means your bottom equals the platform top; kill the fall; you are grounded.

🧠

Knowledge Check

+15 XP

This landing check is your third language writing it. The condition that never changed is…

AThe platform colour

BOnly land while FALLING (vy > 0), the rule that lets you jump up through ledges

CThe vector type

5

⭐

Coins & the HUD

Collectables with the erase-remove idiom for real

Locked

🎯

Goal for this step

Collect coins using the idiom you met in Episode 3, this time for real.

1Coins: std::vector<sf::FloatRect> above the ledges.
2This time USE erase-remove: erase all coins intersecting the player, counting them first with count_if or a manual loop.
3Score += 10 per coin; draw the rest as gold squares; score text top-left (Episode 1 font skill).
4Feel how natural the idiom is on a shrinking pickup list, right tool, right job.

platformer.cpp

std::vector<sf::FloatRect> coins = {
    {205, 300, 18, 18}, {435, 220, 18, 18}, {665, 140, 18, 18} };

sf::FloatRect pb = player.shape.getGlobalBounds();
int before = coins.size();
coins.erase(
    std::remove_if(coins.begin(), coins.end(),
        [&](const sf::FloatRect& c){ return pb.intersects(c); }),
    coins.end());
score += (before - coins.size()) * 10;

✏️

Fill in the Blanks

+15 XP

remove_if shuffles matching items to the end and chops them off. The lambda captures pb with so it can see the player bounds.

🧠

Knowledge Check

+15 XP

The [&] at the start of the lambda means…

AThe lambda is broken

BCapture outside variables by reference, the lambda can read pb from the surrounding scope

CPass by value only

6

🏆

Goal, Death & Structure Review

Win flag, pit respawn, and a look at your architecture

Locked

🎯

Goal for this step

Complete the level and review the clean structure you built.

1Gold flag on the top ledge: touch with all coins gone → WIN state, banner, R restarts.
2Fall past y 480 → respawn at start (reset position and vy).
3Now look at your main(): events → player.update(dt) → collisions → draw. Four readable phases. THAT structure is why classes matter.
4Save this file! Episode 5 adds enemies, camera and levels directly on top.

platformer.cpp

// main loop shape, this is the goal:
while (window.isOpen()) {
    handleEvents(window, player);
    float dt = clock.restart().asSeconds();

    if (state == PLAY) {
        player.update(dt);
        resolveCollisions(player, platforms);
        collectCoins(player, coins, score);
        checkGoal(player, flag, coins, state);
    }

    draw(window, player, platforms, coins, scoreText);
}

⌨️

Code Challenge

+20 XP

The win needs the flag AND an empty coin vector:

platformer.cpp

if (pb.intersects(flag) && coins.())
    state = ;

💡 Hint: Vectors report emptiness with a method; then switch to the winning enum state.

🧠

Knowledge Check

+15 XP

Your main loop reads as four named phases. The biggest benefit is…

AIt compiles faster

BAny bug has an obvious home, physics bug? Look in update. Draw glitch? Look in draw

CIt uses less RAM

Gravity Works!C++ Platformer

Gravity Works!
C++ Platformer