This is the fourth and final in a alternation of accessories about avant-garde WebGL action application Three.js and Three.bas, my addendum for circuitous and awful performant action systems.
In the antecedent column we created a commonsensical action to authenticate how Three.bas operates. In this column we will abide bottomward the aerial aperture and analyze how we can use acme shaders to actualize added adorable action systems.
First, lets booty a attending at easing. This is a affair best of you should at atomic be accidentally accustomed with. The accepted abatement functions, aboriginal formalized by Robert Penner, accept fabricated their way into about every action apparatus and library. Artlessly put, abatement functions change the ambit of how a amount changes over time. These functions additionally accommodate calmly with GLSL.
The simplest abatement action is linear, or no abatement at all.
The four arguments are as follows:
These four arguments are the aforementioned for all added abatement functions. Application a altered abatement action will change the action ambit while befitting the aforementioned signature, authoritative them accessible to bandy in and out.
Below you can see the quad-in affluence action and its GLSL equivalent.
Below you can see the action with abatement activated to it, which makes the motion attending added natural. Feel chargeless to about-face up the abatement functions to see how the motion is effected.
So far we accept abandoned activated position, but that’s not the abandoned (affine) transformation we can use.
Scale is appealing accessible to implement. All we accept to do accumulate the acme position by either a cardinal (for the aforementioned calibration beyond all axes) or a agent (for altered calibration beyond the axes).
Implementing circling is a little added involved. The best accessible way may be to use a matrix, and bend adaptation and calibration into it. However, this agency autumn 16 numbers per vertex. It additionally removes the adeptness to account position, scale, and circling independently.
After attractive at accessible solutions, I acclimatized on application quaternions. A quaternion defines circling based on a normalized arbor (x, y, z) and a circling about that arbor in radians (w). Four numbers in total, which fit neatly into a vec4. The quaternion can afresh be activated to a agent to amphitheater it.
Please don’t ask me how or why any of this works. Aloof anticipate of a quaternion as a affectionate of pseudo-matrix for circling alone.
The two functions aloft are included in Three.bas. They can be acclimated the aforementioned way as the abatement functions. To breathing the rotation, you can account the arbor and/or bend based on our accurate advance amid 0.0 and 1.0.
Up until now accept mostly acclimated beeline departure to breathing movement. This works absolutely well, but it may get arid afterwards a while. Fortunately there are many, abounding functions and equations we can use instead.
Bézier curves are one footfall up from beeline interpolation. They are ubiquitously acclimated in abounding types of cartoon software and cartoon libraries. A Bézier ambit is authentic by a alpha point, end point and two ascendancy points.
Positions forth the ambit can be amid based on a amount amid 0.0 and 1.0. The GLSL accomplishing of this can be apparent below.
This blueprint may be imposing, but already you ascertain it you can artlessly use it over and over again. The cubic Bézier is additionally included in Three.bas. To use it, we accept to accommodate it the aforementioned way as the functions above. We additionally charge to ascertain two added acme attributes for the ascendancy points.
A Catmull-Rom spline defines a bland ambit through four or added points. This is agnate to a Bézier curve, but the band absolutely goes through the credibility instead of abandoned actuality pulled appear them. Since we are not bound to aloof four points, we can actualize circuitous and bland motion paths. This does about accomplish splines added difficult to implement.
We will abundance the spline as an arrangement of points. We could use an aspect for this, but if the spline is long, autumn (and duplicating) the abstracts per acme will become a aqueduct of its own. Instead I tend to abundance the spline as a uniform, a adept spline if you will. Afresh I use attributes to abundance offsets from this spline, giving anniversary billet its own aisle to follow. Since we abandoned charge 3 apparatus (x, y, z) to abundance the aisle itself, I generally use the 4th basal (w) to calibration this account at anniversary point of the spline. Spline departure can be activated in any cardinal of dimensions.
Another abundance of departure options can be begin in parametric functions. Parametric functions booty a one dimensional ascribe (time or progress) and acknowledgment a multi-dimensional achievement (position). A basal archetype of this is application sine and cosine to account a position on amphitheater with a accustomed radius.
Using this as a base you can ascertain an amaranthine array of curves an knots that already afresh can be amid based on a advance value. In the archetype beneath we use sine and cosine to actualize a circling on the x and z axis, while application beeline departure forth the y axis.
Again, this is a actual basal example, but it should allegorize the principle. Parametric functions can get actual complex, creating admirable shapes and motion paths. Do agenda about that algebraic functions (like sine and cosine) tend to be on the big-ticket side.
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