SDL_Chomik: Ten Monkeys

Using Ranges and Random Generators in SDL_Chomik

In the previous SDL_Chomik article, we animated a single blue monkey drifting across the screen. This time, we will take the idea one step further. Instead of one, we’ll unleash ten monkeys! Each monkey starts at a random position and moves steadily toward the right edge of the window. When a monkey exits the screen, it respawns at a fresh random vertical position, starting again from the left.

This small change introduces two powerful features of Chomik:

• Integer ranges: <initialize blue monkey (MONKEY:1..10)> creates ten monkeys in a compact, declarative way.

• Random number streams: two separate streams provide randomized x and y positions for initializing and resetting our monkeys.

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The Code

<create new image "chomik.png">;
let chomik image index = <the created image index>;
<create new image "background.png">;
let background image index = <the created image index>;
<create new image "blue_monkey.png">;
let blue monkey image index = <the created image index>;

<create new input random number stream "integer" 0 <the sdl window height>>;
let my random vertical stream index=<the created stream index>;
<create new input random number stream "integer" 0 <the sdl window width>>;
let my random horizontal stream index=<the created stream index>;

let initialize blue monkey (M:integer) = value code
{
let monkey index = value integer [(M:integer)];
let the read from stream source stream index = <my random vertical stream index>;
<read from stream "integer">;
let blue monkey <monkey index> y = <the read from stream result "integer">;

let the read from stream source stream index = <my random horizontal stream index>;
<read from stream "integer">;
let blue monkey <monkey index> x = <the read from stream result "integer">;
};

<initialize blue monkey (MONKEY:1..10)>;

let reset blue monkey (M:integer) on greater = value code
{
let monkey index = value integer [(M:integer)];
let blue monkey <monkey index> x = value integer -128;
let the read from stream source stream index = <my random vertical stream index>;
<read from stream "integer">;
let blue monkey <monkey index> y = <the read from stream result "integer">;
};

let reset blue monkey (M:integer) if needed = value code
{
let monkey index = value integer [(M:integer)];
<compare "integer" <blue monkey <monkey index> x> <the sdl window width>>;
<reset blue monkey <monkey index> on <the compare result>>;
};

let move blue monkey (M:integer) = value code
{
let monkey index = value integer [(M:integer)];
<add "integer" <blue monkey <monkey index> x> 3>;
let blue monkey <monkey index> x = <the add result "integer">;
<reset blue monkey <monkey index> if needed>;
};

let sdl loop body = value code
{
<show image <background image index> 0 0 >;
<show image <chomik image index> 0 0 >;
<show image <blue monkey (MONKEY:1..10) x> <blue monkey (MONKEY:1..10) y>>;
<move blue monkey (MONKEY:1..10)>;
};
<sdl loop>;

How It Works

1. Random generators: We create two streams:

   • one for vertical positions (0 .. window height),

   • one for horizontal positions (0 .. window width)

Each monkey pulls its starting coordinates from these streams.

2. Initialization: With <initialize blue monkey (MONKEY:1..10)>, ten monkeys are defined at once. Each monkey gets its own x and y values.

3. Movement: Each monkey moves three pixels to the right in every frame:
   <add "integer" <blue monkey <monkey index> x> 3>;
   If it goes past the window width, we reset its x to -128 and pick a new random y.

4. Rendering:
   The background, base "chomik" image, and all ten monkeys are drawn in each loop iteration.

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What to Notice

• Integer ranges make it natural to express “ten monkeys” without repetitive code.

• Streams provide a clean source of randomness—ideal for procedural animation.

This example highlights how SDL_Chomik’s declarative style lets you think in terms of behaviors rather than loops or conditions. You define what happens when a monkey moves, reaches an edge, or respawns—and the runtime handles the rest.

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Next Steps

From here, you can:

• Vary each monkey’s speed by adding another random generator.

• Use different sprites for different monkeys.

• Make the monkeys bounce instead of respawn.

The combination of ranges, randomness, and reset behaviors gives you a solid toolbox for creating lively, unpredictable animations in SDL_Chomik.