C++ objects

Registering C++ objects

Anything the manifest cannot express (updaters, computed geometry, quantities) is defined in C++ and registered under a name, then placed by the manifest with object: name.

    auto spot = Mesh::Add("spot.obj");
    spot->setUpdater([](TimeObject t){ /* ... */ }); // configure animation
    deck.registerObject("wobbly_spot",spot);

registerObject accepts several forms:

registerObject(name, std::function<PrimitiveInSlide()>): factory, primitive + state

registerObject(name, std::function<PrimitivePtr()>): factory, default state

registerObject(name, PrimitivePtr) / registerObject(name, PrimitiveInSlide): already-built

registerObject(name, PrimitiveGroup) (or its factory): several primitives placed together

Factories are called lazily, the first time the manifest uses the name, and the result is cached: a hot reload re-places the same primitive instead of rebuilding it, so meshes, textures and compiled latex survive edits.

With tunable parameters

Registered objects combine naturally with tunable parameters: declare the parameter next to the updater that reads it, and tune the animation live while editing the deck.

deck.registerObject("wobbly_spot", []() {
    auto amp = Params::Add("spot/amplitude", 0.2, 0., 0.5);
    auto spot = Mesh::Add("spot.obj");
    spot->setUpdater([=](TimeObject t){
        deform(spot, (scalar)amp, t.inner_time);
    });
    return spot;
});

Synchronizing with the deck : keyframes

An updater branching on t.relative_frame_number assumes a step structure that the manifest can freely reorder. Instead, mark the relevant frame in the manifest with a keyframe and test it by name: the branch follows the label wherever it moves:

- object: wobbly_spot
- step
- keyframe: noise_on

spot->setUpdater([=](TimeObject t){
    if (t.afterKeyframe("noise_on"))
        addNoise(spot, t.inner_time);
});

afterKeyframe is true from the marked frame on, atKeyframe exactly on it, beforeKeyframe strictly before. An unknown label warns once in the terminal and answers false.