9. Make a complete game¶
Chili Catch is a small but complete game that uses everything from the earlier lessons. Chilis fall from the sky and you catch them in a basket: chilis are worth 1 point, coins 5, hearts give you a life back, and bombs take one away. Everything falls faster as your score goes up, and your best score is saved.
It's about 330 lines in one file, docs/examples/chili-catch/chili-catch.cpp. This page walks through it section by section; the full source is at the end.
Game states¶
A game is usually in one of a few states: a title screen, playing, paused, game over. Keeping the state in one variable and switching on it keeps each part of the code simple.
enum class State { title, playing, game_over };
struct Item {
Sprite sprite;
Vec2 pos;
float speed;
};
struct Spark {
Vec2 pos, vel;
uint32_t born;
};
struct SaveData {
uint32_t version = 1;
uint32_t best = 0;
};
State state = State::title;
SaveData save;
float player_x = 60;
bool facing_left = false;
bool moving = false;
std::vector<Item> items;
std::vector<Spark> sparks;
uint32_t score = 0;
int lives = start_lives;
uint32_t next_spawn = 0;
uint32_t hurt_until = 0; // flash the player after a bomb
bool new_best = false;
Tween title_bob;
Itemis anything falling: which sprite it is, where it is, and how fast it falls.Sparkis one particle of a burst.SaveDataholds the best score, with a version number as in Saving progress.- The rest is the state of the current round: the player's position, the falling items, the score, lives, and when to spawn the next item.
Sound¶
Each kind of sound gets its own channel, set up once. Every effect has sustain = 0 so it ends by itself.
void setup_sound() {
// channel 0: pickup blip
channels[0].waveforms = Waveform::SQUARE;
channels[0].attack_ms = 2;
channels[0].decay_ms = 80;
channels[0].sustain = 0;
channels[0].volume = 0x6000;
// channel 1: bomb explosion
channels[1].waveforms = Waveform::NOISE;
channels[1].attack_ms = 5;
channels[1].decay_ms = 400;
channels[1].sustain = 0;
// channel 2: game over / extra life tune
channels[2].waveforms = Waveform::TRIANGLE;
channels[2].attack_ms = 10;
channels[2].decay_ms = 300;
channels[2].sustain = 0;
}
void play(int channel, uint16_t frequency) {
channels[channel].frequency = frequency;
channels[channel].trigger_attack();
}
Starting, ending and spawning¶
void save_best() {
write_save(save);
}
void burst(Vec2 pos, int count) {
for(int i = 0; i < count; i++) {
float angle = (blit::random() % 628) / 100.0f;
float speed = 0.3f + (blit::random() % 100) / 100.0f;
sparks.push_back({pos, Vec2(cosf(angle) * speed, sinf(angle) * speed - 0.5f), now()});
}
}
void start_game(uint32_t time) {
state = State::playing;
items.clear();
sparks.clear();
score = 0;
lives = start_lives;
player_x = 60;
next_spawn = time + 500;
new_best = false;
}
void end_game() {
state = State::game_over;
new_best = score > save.best;
if(new_best) {
save.best = score;
save_best();
}
play(2, 196);
}
void spawn_item(uint32_t time) {
// pick what falls: mostly chilis, some coins and bombs, the odd heart
int roll = blit::random() % 100;
Sprite sprite = CHILI;
if(roll >= 97) sprite = HEART;
else if(roll >= 75) sprite = BOMB;
else if(roll >= 63) sprite = COIN;
// everything falls faster as the score goes up
float speed = 0.35f + std::min<uint32_t>(score, 200) / 250.0f + (blit::random() % 30) / 100.0f;
items.push_back({sprite, Vec2(float(4 + blit::random() % 116), -8.0f), speed});
// and arrives more often
uint32_t gap = 900 - std::min<uint32_t>(score * 4, 600);
next_spawn = time + gap / 2 + blit::random() % gap;
}
start_game()resets the round.end_game()checks for a new best and saves straight away, because the player might switch the console off on the game over screen.spawn_item()rolls a random number to decide what falls. 63% of items are chilis, 12% coins, 22% bombs and 3% hearts. Changing these numbers changes how the game feels more than almost anything else.- Difficulty comes from two numbers that grow with the score: how fast items fall, and how long until the next one. Both are capped with
std::minso the game stays playable.
Init¶
void init() {
set_screen_mode(ScreenMode::hires);
screen.sprites = Surface::load(asset_sprites);
if(!read_save(save) || save.version != 1)
save = SaveData();
on_quit = save_best;
setup_sound();
title_bob.init(tween_sine, -3.0f, 3.0f, 1200, -1);
title_bob.start();
}
This loads the spritesheet, loads the save and registers save_best as on_quit, sets up the sound channels, and starts the tween that makes the title bob up and down.
Update: playing¶
void update_playing(uint32_t time) {
moving = false;
if(buttons & Button::DPAD_LEFT) {
player_x -= player_speed;
facing_left = true;
moving = true;
}
if(buttons & Button::DPAD_RIGHT) {
player_x += player_speed;
facing_left = false;
moving = true;
}
player_x = std::max(0.0f, std::min(player_x, float(screen_w - 16)));
if(time >= next_spawn)
spawn_item(time);
// the basket is the 16 pixels in front of the player's hands
Rect basket(int(player_x), ground_y - 14, 16, 6);
for(auto it = items.begin(); it != items.end();) {
it->pos.y += it->speed;
Rect item_rect(Point(it->pos), Size(8, 8));
bool caught = item_rect.intersects(basket);
bool missed = it->pos.y > ground_y;
if(caught) {
switch(it->sprite) {
case CHILI: score += 1; play(0, 880); break;
case COIN: score += 5; play(0, 1320); break;
case HEART:
lives = std::min(lives + 1, max_lives);
play(2, 660);
break;
case BOMB:
lives--;
hurt_until = time + 600;
play(1, 200);
break;
default: break;
}
burst(it->pos + Vec2(4, 4), it->sprite == BOMB ? 20 : 8);
} else if(missed && it->sprite == CHILI) {
// a dropped chili costs nothing, but gives a little puff
burst(Vec2(it->pos.x + 4, ground_y), 3);
}
if(caught || missed)
it = items.erase(it);
else
++it;
}
if(lives <= 0)
end_game();
}
- Movement uses held buttons and a fixed speed per update, and clamps the player to the screen.
- Collision is a rectangle test:
Rect::intersects()between each item and the basket's rectangle. - Items are removed from the vector while looping over it.
erase()returns the next iterator, which is the safe way to do that.
Update: every state¶
void update(uint32_t time) {
switch(state) {
case State::title:
if(buttons.pressed & Button::A)
start_game(time);
break;
case State::playing:
update_playing(time);
break;
case State::game_over:
if(buttons.pressed & Button::A)
start_game(time);
break;
}
// sparks fly outwards, fall, and fade after 600 ms
for(auto &s : sparks) {
s.pos += s.vel;
s.vel.y += 0.03f;
}
sparks.erase(std::remove_if(sparks.begin(), sparks.end(),
[time](const Spark &s) { return time - s.born > 600; }), sparks.end());
}
update() hands over to the right code for the current state. On the title and game over screens, A starts a new round.
Sparks¶
The sparks are updated in every state so a burst finishes even after the game ends. Each spark is a position and velocity with a bit of gravity, removed after 600 ms with the erase-remove idiom. This is the simple alternative to a ParticleGenerator for one-off bursts.
Render¶
void draw_background() {
for(int y = 0; y < ground_y; y++) {
screen.pen = Pen(100 + y / 2, 160 + y / 4, 235);
screen.h_span(Point(0, y), screen_w);
}
for(int x = 0; x < screen_w; x += 8) {
screen.sprite(GRASS, Point(x, ground_y));
screen.sprite(DIRT, Point(x, ground_y + 8));
}
}
void draw_hud() {
screen.pen = Pen(0, 0, 0, 120);
screen.rectangle(Rect(0, 0, screen_w, 11));
for(int i = 0; i < lives; i++)
screen.sprite(HEART, Point(2 + i * 9, 2));
screen.pen = Pen(255, 255, 255);
screen.text(std::to_string(score), minimal_font, Point(screen_w - 3, 2), true, TextAlign::top_right);
}
void draw_player(uint32_t time) {
// flash while hurt
if(time < hurt_until && (time / 80) % 2)
return;
uint16_t frame = moving && (time / 150) % 2 ? PLAYER_2 : PLAYER_1;
uint8_t flip = facing_left ? SpriteTransform::HORIZONTAL : SpriteTransform::NONE;
int x = int(player_x);
// the player and the basket they hold out in front
screen.sprite(frame, Point(facing_left ? x + 8 : x, ground_y - 8), flip);
screen.sprite(BASKET, Point(facing_left ? x : x + 8, ground_y - 13));
}
void render(uint32_t time) {
draw_background();
for(auto &item : items)
screen.sprite(item.sprite, Point(item.pos));
if(state != State::title)
draw_player(time);
for(auto &s : sparks) {
int age = time - s.born;
screen.pen = Pen(255, 220, 80, 255 - age * 255 / 600);
screen.pixel(Point(s.pos));
}
if(state == State::playing) {
draw_hud();
return;
}
// title and game over panels
screen.pen = Pen(0, 0, 0, 150);
screen.rectangle(Rect(10, 24, 108, 64));
screen.pen = Pen(255, 255, 255);
int bob = int(title_bob.value);
if(state == State::title) {
screen.sprite(CHILI, Point(56, 30 + bob), Point(4, 4), 2.0f);
screen.text("CHILI CATCH", fat_font, Point(64, 48), true, TextAlign::center_center);
screen.text("Best: " + std::to_string(save.best), minimal_font, Point(64, 62), true, TextAlign::center_center);
} else {
screen.text("GAME OVER", fat_font, Point(64, 36 + bob), true, TextAlign::center_center);
screen.text("Score: " + std::to_string(score), minimal_font, Point(64, 54), true, TextAlign::center_center);
screen.text(new_best ? "New best!" : "Best: " + std::to_string(save.best), minimal_font, Point(64, 64), true, TextAlign::center_center);
}
if((time / 500) % 2)
screen.text("Press A", minimal_font, Point(64, 78), true, TextAlign::center_center);
}
Drawing goes back to front: sky, ground, falling items, the player, sparks, and then either the HUD or a title or game over panel on top.
- The sky is a gradient of horizontal spans, one per line.
- The player sprite is flipped with
SpriteTransform::HORIZONTALwhen facing left, and the basket moves to that side. - After a bomb, the player flashes by skipping their drawing on alternate 80 ms periods.
- Spark colour fades with age through the pen's alpha.
- The panels use a translucent black rectangle so the game shows through.
Ideas to extend it¶
- Pause menu: a
pausedstate entered with MENU, drawn as another panel. - Combos: count chilis caught in a row and give a bonus every ten.
- Music: a looping tune on a spare channel, using a Timer to step through notes.
- Power-ups: a star that makes the basket wider for ten seconds, with a Timer to end it.
- Statistics: total chilis caught across all games, kept in
SaveData(remember to bumpversion).
Full source¶
chili-catch.cpp
// Chili Catch: a complete small game.
//
// Move with the d-pad and catch the falling chilis. Coins are worth more,
// hearts give a life back, and bombs take one away. The game speeds up as
// the score grows, and the best score is saved.
//
// It brings together the pieces from the tutorials: the game loop, input,
// sprites, sound, saves, tweens and simple particles.
#include <vector>
#include "32blit.hpp"
#include "assets.hpp"
using namespace blit;
// ---------------------------------------------------------------------------
// constants
constexpr int screen_w = 128, screen_h = 128;
constexpr int ground_y = 112; // top of the grass
constexpr float player_speed = 1.2f; // pixels per update (update runs 100 times a second)
constexpr int start_lives = 3, max_lives = 5;
// sprite indices in examples/shared/sprites.png
enum Sprite : uint16_t {
CHILI = 0, PLAYER_1 = 1, PLAYER_2 = 2, HEART = 3, COIN = 4, BOMB = 5, STAR = 6, BASKET = 7, GRASS = 8, DIRT = 9
};
// ---------------------------------------------------------------------------
// game state
enum class State { title, playing, game_over };
struct Item {
Sprite sprite;
Vec2 pos;
float speed;
};
struct Spark {
Vec2 pos, vel;
uint32_t born;
};
struct SaveData {
uint32_t version = 1;
uint32_t best = 0;
};
State state = State::title;
SaveData save;
float player_x = 60;
bool facing_left = false;
bool moving = false;
std::vector<Item> items;
std::vector<Spark> sparks;
uint32_t score = 0;
int lives = start_lives;
uint32_t next_spawn = 0;
uint32_t hurt_until = 0; // flash the player after a bomb
bool new_best = false;
Tween title_bob;
// ---------------------------------------------------------------------------
// sound
void setup_sound() {
// channel 0: pickup blip
channels[0].waveforms = Waveform::SQUARE;
channels[0].attack_ms = 2;
channels[0].decay_ms = 80;
channels[0].sustain = 0;
channels[0].volume = 0x6000;
// channel 1: bomb explosion
channels[1].waveforms = Waveform::NOISE;
channels[1].attack_ms = 5;
channels[1].decay_ms = 400;
channels[1].sustain = 0;
// channel 2: game over / extra life tune
channels[2].waveforms = Waveform::TRIANGLE;
channels[2].attack_ms = 10;
channels[2].decay_ms = 300;
channels[2].sustain = 0;
}
void play(int channel, uint16_t frequency) {
channels[channel].frequency = frequency;
channels[channel].trigger_attack();
}
// ---------------------------------------------------------------------------
// helpers
void save_best() {
write_save(save);
}
void burst(Vec2 pos, int count) {
for(int i = 0; i < count; i++) {
float angle = (blit::random() % 628) / 100.0f;
float speed = 0.3f + (blit::random() % 100) / 100.0f;
sparks.push_back({pos, Vec2(cosf(angle) * speed, sinf(angle) * speed - 0.5f), now()});
}
}
void start_game(uint32_t time) {
state = State::playing;
items.clear();
sparks.clear();
score = 0;
lives = start_lives;
player_x = 60;
next_spawn = time + 500;
new_best = false;
}
void end_game() {
state = State::game_over;
new_best = score > save.best;
if(new_best) {
save.best = score;
save_best();
}
play(2, 196);
}
void spawn_item(uint32_t time) {
// pick what falls: mostly chilis, some coins and bombs, the odd heart
int roll = blit::random() % 100;
Sprite sprite = CHILI;
if(roll >= 97) sprite = HEART;
else if(roll >= 75) sprite = BOMB;
else if(roll >= 63) sprite = COIN;
// everything falls faster as the score goes up
float speed = 0.35f + std::min<uint32_t>(score, 200) / 250.0f + (blit::random() % 30) / 100.0f;
items.push_back({sprite, Vec2(float(4 + blit::random() % 116), -8.0f), speed});
// and arrives more often
uint32_t gap = 900 - std::min<uint32_t>(score * 4, 600);
next_spawn = time + gap / 2 + blit::random() % gap;
}
// ---------------------------------------------------------------------------
// init / update / render
void init() {
set_screen_mode(ScreenMode::hires);
screen.sprites = Surface::load(asset_sprites);
if(!read_save(save) || save.version != 1)
save = SaveData();
on_quit = save_best;
setup_sound();
title_bob.init(tween_sine, -3.0f, 3.0f, 1200, -1);
title_bob.start();
}
void update_playing(uint32_t time) {
moving = false;
if(buttons & Button::DPAD_LEFT) {
player_x -= player_speed;
facing_left = true;
moving = true;
}
if(buttons & Button::DPAD_RIGHT) {
player_x += player_speed;
facing_left = false;
moving = true;
}
player_x = std::max(0.0f, std::min(player_x, float(screen_w - 16)));
if(time >= next_spawn)
spawn_item(time);
// the basket is the 16 pixels in front of the player's hands
Rect basket(int(player_x), ground_y - 14, 16, 6);
for(auto it = items.begin(); it != items.end();) {
it->pos.y += it->speed;
Rect item_rect(Point(it->pos), Size(8, 8));
bool caught = item_rect.intersects(basket);
bool missed = it->pos.y > ground_y;
if(caught) {
switch(it->sprite) {
case CHILI: score += 1; play(0, 880); break;
case COIN: score += 5; play(0, 1320); break;
case HEART:
lives = std::min(lives + 1, max_lives);
play(2, 660);
break;
case BOMB:
lives--;
hurt_until = time + 600;
play(1, 200);
break;
default: break;
}
burst(it->pos + Vec2(4, 4), it->sprite == BOMB ? 20 : 8);
} else if(missed && it->sprite == CHILI) {
// a dropped chili costs nothing, but gives a little puff
burst(Vec2(it->pos.x + 4, ground_y), 3);
}
if(caught || missed)
it = items.erase(it);
else
++it;
}
if(lives <= 0)
end_game();
}
void update(uint32_t time) {
switch(state) {
case State::title:
if(buttons.pressed & Button::A)
start_game(time);
break;
case State::playing:
update_playing(time);
break;
case State::game_over:
if(buttons.pressed & Button::A)
start_game(time);
break;
}
// sparks fly outwards, fall, and fade after 600 ms
for(auto &s : sparks) {
s.pos += s.vel;
s.vel.y += 0.03f;
}
sparks.erase(std::remove_if(sparks.begin(), sparks.end(),
[time](const Spark &s) { return time - s.born > 600; }), sparks.end());
}
void draw_background() {
for(int y = 0; y < ground_y; y++) {
screen.pen = Pen(100 + y / 2, 160 + y / 4, 235);
screen.h_span(Point(0, y), screen_w);
}
for(int x = 0; x < screen_w; x += 8) {
screen.sprite(GRASS, Point(x, ground_y));
screen.sprite(DIRT, Point(x, ground_y + 8));
}
}
void draw_hud() {
screen.pen = Pen(0, 0, 0, 120);
screen.rectangle(Rect(0, 0, screen_w, 11));
for(int i = 0; i < lives; i++)
screen.sprite(HEART, Point(2 + i * 9, 2));
screen.pen = Pen(255, 255, 255);
screen.text(std::to_string(score), minimal_font, Point(screen_w - 3, 2), true, TextAlign::top_right);
}
void draw_player(uint32_t time) {
// flash while hurt
if(time < hurt_until && (time / 80) % 2)
return;
uint16_t frame = moving && (time / 150) % 2 ? PLAYER_2 : PLAYER_1;
uint8_t flip = facing_left ? SpriteTransform::HORIZONTAL : SpriteTransform::NONE;
int x = int(player_x);
// the player and the basket they hold out in front
screen.sprite(frame, Point(facing_left ? x + 8 : x, ground_y - 8), flip);
screen.sprite(BASKET, Point(facing_left ? x : x + 8, ground_y - 13));
}
void render(uint32_t time) {
draw_background();
for(auto &item : items)
screen.sprite(item.sprite, Point(item.pos));
if(state != State::title)
draw_player(time);
for(auto &s : sparks) {
int age = time - s.born;
screen.pen = Pen(255, 220, 80, 255 - age * 255 / 600);
screen.pixel(Point(s.pos));
}
if(state == State::playing) {
draw_hud();
return;
}
// title and game over panels
screen.pen = Pen(0, 0, 0, 150);
screen.rectangle(Rect(10, 24, 108, 64));
screen.pen = Pen(255, 255, 255);
int bob = int(title_bob.value);
if(state == State::title) {
screen.sprite(CHILI, Point(56, 30 + bob), Point(4, 4), 2.0f);
screen.text("CHILI CATCH", fat_font, Point(64, 48), true, TextAlign::center_center);
screen.text("Best: " + std::to_string(save.best), minimal_font, Point(64, 62), true, TextAlign::center_center);
} else {
screen.text("GAME OVER", fat_font, Point(64, 36 + bob), true, TextAlign::center_center);
screen.text("Score: " + std::to_string(score), minimal_font, Point(64, 54), true, TextAlign::center_center);
screen.text(new_best ? "New best!" : "Best: " + std::to_string(save.best), minimal_font, Point(64, 64), true, TextAlign::center_center);
}
if((time / 500) % 2)
screen.text("Press A", minimal_font, Point(64, 78), true, TextAlign::center_center);
}
Build it with the other examples, or copy it into a project made from the template along with docs/examples/shared/sprites.png, and put it on your console. Have fun.