Parrot

Parrot is a game engine written in C++ created for educational purposes. The engine lets you develop games using custom asset formats and C++ scripts.

technologies used:

• window-api: glfw
• graphics-api: opengl using glad
• assets: nlohmann/json, nothings/stb, tinyobjloader/tinyobjloader

Architecture

modules:

• core create, run and destroy apps and playing-units + connect to client code
• window create, update and destroy physical windows
• ecs provide ecs api with scenes, entities and components
• graphics handle graphics data like meshes or materials and communicate with the gpu
• asset-manager manage the client asset-directory and handle the assets lifetimes

besides the core module, no modules depend on each other

Scripting

In order to have logic in your game, you can add scripts written in C++.

Example Script

#include "path/to/src/client.hh"

class ScriptName : public Script {
    ScriptName(Entity& entity)
        : entity(entity) {}

    virtual bool resolveEvent(const Event& e) override {
        if (auto* mouse_move = e.getMouseMove()) {
            std::cout << "Mouse was moved!" << std::endl;
        }
        return false;
    }
    virtual void onUpdate(float32 delta_time) override {
        std::cout << "I'm getting updated!" << std::endl;
    }

    Entity& entity;
}

this is a script that you can attach to entities.

You can add scripts to

• Apps
• Playing-Units (Window, Scene)
• Entities

Important

in the current development state you can only attach scripts to entities

Asset Formats

For now, all assets are stored in a .json format.

handles can be either uuids (i.e. numbers), filepaths (i.e. strings) or inlined (i.e. objects)

Format: ".app.json"

{
    // general
    "name": "App Name", // default: "Unnamed App"
    "main": [
        "<window-handle>",
        "<scene-handle>",
        [ "ScriptName1", /* ... */ ] // optional
    ],
    
    // assets
    "loading-policy": "app|scene|lazy", // default: "lazy"
    "unloading-policy": "app|scene|unused" // default: "app"

    // scripts
    "scripts": [ // default: []
        "ScriptName1", /* ... */
    ]
}

Format: ".wndw.json"

{
    "uuid": 1234567889,
    "title": "Window Title", // default: "Untitled Window"
    "size": [ 1080, 720 ], // default: [ 1080, 720 ]
}

Format: ".scn.json

{
    // general
    "uuid": 1234567889,
    "name": "Scene Name", // default: "Unnamed Scene"
    
    // hierarchy
    "root": "<entity-handle>" // default: null
}

Format: ".entt.json"

{
    // general
    "uuid": 1234567889,
    "tag": "Entity Tag", // default: "Entity"

    // transform
    "transform": { // default: {}
        "position": [ 0, 0, 0 ], // default: [ 0, 0, 0 ]
        "rotation": [ 0, 0, 0 ], // default: [ 0, 0, 0 ]
        "scale": [ 1, 1, 1 ] // default: [ 1, 1, 1 ]
    },
    // children
    "children": [ // default: []
        "<entity-handle>", /* ... */
    ],
    // components
    "components": { // default: {}
        "component_name": {
            /* data depends on component */
        }, /* ... */
    },
    // scripts
    "scripts": [ // default: []
        "ScriptName1", /* ... */
    ]
}

Format: ".mesh.json"

{
    // general
    "uuid": 1234567889,
    "resource": "path/to/mesh.obj"
}

Format: ".shader.json"

{
    // general
    "uuid": 1234567889,
    "vertex": {
        "resource": "path/to/vertex_shader.vs.glsl"
    },
    "fragment": {
        "resource": "path/to/fragment_shader.fs.glsl"
    }
}