When adding bindings for primitives, materials, … the code required for exporting functionality to the scripting language was mostly complete: you only needed to add a line or two in order to make your new extension work in the scripting language.
For easing functions, things are slightly more complicated.
1.1. Easing Library
The scripting language works with "library objects": these are objects that group factory functions.
Examples of such library objects are
It is our goal to create a new library Easing which will group together all easing functions.
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Create the EasingLibrary type.
The easing functions are part of the math module, so open scripting/math-module.cpp.
This is where you’ll need to perform the following steps.
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Define a new empty struct EasingLibrary.
Put it inside the anonymous namespace that already exists within the file.
You can take a look at SamplerLibrary in scripting/samplers-module.cpp or RaytracerLibrary in scripting/raytracing-module.cpp for guidance.
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Find the function raytracer::scripting::_private_::create_math_module().
Its responsibility is to add all math-related bindings.
You can see it delegates this work to auxiliary functions such as add_points_and_vectors to add all Point2D, Point3D, Vector2D and Vector3D related functionality to the scripting language.
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Add an extra call to add_easing to this function.
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Define add_easing in the anonymous namespace.
Its signature (parameter types, return type) should match the other functions.
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add_easing should start with creating a EasingLibrary object.
This object should be created on the heap, as it survives the call to add_easing.
This means making use of shared_ptr.
For guidance, go look at create_samplers_module() in scripting/samplers-module.cpp.
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Once you created the EasingLibrary object, you need to expose it to the scripting language by associating the identifier "Easing" with this object.
Hint: this is done using add_global_const.
You can find examples of how to do it in the other scripting modules.
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Define a macro BIND that can be used to easily add bindings to EasingLibrary members.
Hint: the macro makes use of the add member of Chaiscript modules.
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The EasingLibrary is still empty, so you cannot add bindings yet.
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1.2. Ease function
Easing functions need to be applied on animations.
Take a look to the preview scripts in the extensions for easing functions, such as bounce.
You’ll find that first, an animation from A to B is created, and then, in a second step, an easing function is applied to it using the Animations.ease function.
You will need to define this very function in order to be able to make use of your easing functions.
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Define the Animations.ease function.
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Open scripting/animation-module.cpp.
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Look for the AnimationLibrary.
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Define a function template ease_animation.
The template parameter T represents what kind of animation needs to be eased.
For example, we can ease Animation<double>, Animation<Point3D>, Animation<Angle>, or any other sort of animation.
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The ease_animation function expects two parameters: an animation of type Animation<T>, and an easing function of type math::functions::EasingFunction.
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The ease_animation function returns an Animation<T>.
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The body of ease_animation is quite simple: it calls the already existing function ease with the same parameters and returns its value.
This ease function is defined in animation/ease-animation.h.
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Find the function raytracer::scripting::_private_::create_animation_module().
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The scripting language itself does not support templates, so we will need to expose ease_animation repeatedly, once for each animatable type T.
By our ray tracer can animate doubles, Angles and Point3Ds.
For each "animatable" type T, use the BIND_AS macro to expose ease_animation<T> as ease (e.g. BIND_AS(ease_animation<double>, ease)).
You can reuse the same name ease for each T: the scripting language supports overloading and will automatically pick the right binding for you.
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