| name | machin-game-demo-flappy |
| description | Build, run, and modify machin-game-demo-flappy — a Flappy-Bird-style native raylib desktop game in machin (MFL). Use when working on this repo, or as a worked example of textures/sprites over the C FFI (Texture2D handles, f32-field Rectangle/Vector2 structs, sprite sheets, rotation) and machin's int/float conversion rules. |
machin-game-demo-flappy
A Flappy-Bird-style game as a native raylib desktop window, written in machin (MFL). It is the reference example for textures/sprites in machin (the FFI counterpart to machin-game-demo-2048, which used only shapes + text).
The shared game-dev setup, build-and-verify workflow, and the cross-cutting caveats/gotchas (esp. the int/float rule this game drove float() to fix) live in the canonical machin-gamedev skill. This file is flappy's specifics.
Build & run
./build.sh
./machin-game-demo-flappy
Needs machin v0.43.0+ (uses float()), a C compiler, raylib, and a display.
- System raylib (
apt-get install libraylib-dev, brew install raylib): detected via pkg-config/headers, built directly.
- No root:
build.sh downloads raylib's prebuilt static release into vendor/ and injects cflags/:libraylib.a into a throwaway .mfl; the committed flappy.src stays system-style.
Controls: Space / left-click to flap, Space to restart, Esc to quit.
Textures over the FFI
The whole graphics surface is the extern "raylib" { … } block; everything else is pure MFL. Beyond 2048's scalars + Color, this game drives:
| MFL | raylib C | FFI feature |
|---|
cstruct Texture2D { id u32 width i32 height i32 mipmaps i32 format i32 } | Texture2D (all-int handle) | a by-value struct returned from LoadTexture |
cstruct Rectangle { x f32 y f32 width f32 height f32 }, Vector2 { x f32 y f32 } | same | by-value structs with f32 fields |
fn DrawTextureRec(Texture2D, Rectangle, Vector2, Color) | same | struct args by value |
fn DrawTexturePro(Texture2D, Rectangle, Rectangle, Vector2, f32, Color) | same | + an f32 rotation scalar |
Tricks worth copying:
- Sprite sheet: the bird is one 144×48 PNG of three 48×48 frames; the source
Rectangle{float(frame*48), 0, 48, 48} selects the frame, DrawTexturePro rotates it around its center (origin = Vector2{24,24}) by an angle derived from velocity.
- Flip with a negative source height: the top and bottom pipes share one texture; the top one is drawn with
Rectangle{0,0,88,-600} (negative height ⇒ vertical flip) so its cap faces down. No second asset.
- Tiled scroll: the ground is drawn as two copies at
gx and gx+WIN_W, with gx = -(scroll % WIN_W).
The int/float gotcha (important)
MFL has no implicit int→float. A flexible numeric literal (48, 560) promotes against a float, but a concrete int does not — and that's a hard int vs float compile error. Concrete ints come from: a function return (even func BIRD_X() { n = 110 }), byte_at, len, a typed parameter, an int-slice element, and they also can't go straight into an f32/f64 cstruct field.
Fixes used here (all need machin v0.43.0+ float()):
- World-coordinate constants return floats (
GROUND_Y() { n = 560.0 }) so they mix with bird_y.
rnd_gap wraps its byte_at math: 160.0 + float((byte_at(r,0) << 8 | byte_at(r,1)) % 260).- A concrete int into an
f32 field is wrapped: Rectangle{float(frame*48), 0, 48, 48}.
- Loop indices stay pure
int: init_pipes uses a float accumulator (x = x + SPACING()), never i * SPACING() (which would drag the index to float).
- Going the other way for an FFI
i32 arg: int(GROUND_Y()).
Rule of thumb: keep a value in one numeric world; cross with float(x) / int(x) explicitly.
Modifying
- Difficulty:
GAP_H (gap half-height), SPACING (pipe distance), SPEED (scroll), and the 0.45 gravity / -7.5 flap in main.
- Art: replace the PNGs in
assets/ (keep the bird sheet 3×48px frames, or adjust frame*48 and the frame count).
- Window:
WIN_W/WIN_H (stay int — they feed InitWindow/UI).
- After any edit to
flappy.src, re-run ./build.sh (never hand-edit flappy.mfl — it is generated).
