Regarding the issue of in/out value in animation key info.

[849675273]

Hello guys, I'm a new in Max. I've encountered an issue regarding the animation curves in keyframes.

As everyone knows, in the Motion → Parameters → Key Info (Advanced) window, there are two editable values related to animation easing.

As shown in my screenshot, I checked the official documentation and found that the bottom row represents the tangent length of the keyframe.

However, what confuses me is the top row. I feel like it should represent some kind of slope, but I'm not entirely sure.

When you manipulate the Bézier curve in the Curve Editor, this value changes accordingly.

The key point is that I want to understand how it is calculated. If you're familiar with Bézier curves, you know that they have two control points.

If this value truly represents the slope, then its calculation should be:

（Control Pointy−Start Pointy）/ Δx

However, I'm not entirely sure if that's how it works.

Then the slope in the image should be either -1 or 1, depending on the direction.

But in the Key Info window, it shows 0.235 instead.

Can someone help explain why this is the case?

[leeminardi]

@849675273   First off, the Key Info (Advanced) dialog box is not very intuitive.  You have to look at the x, y, and z values to set the slope of the curve at the specific keyframe.  For example, the following image shows the teapot at the second of 2 keyframes. The incoming slope is 135° as measure from the X axis.  The curve has a value of -5 for x, and +5 for y.

which is a vector at 135°.    The magnitude of the values sets the length of the Bezier spline handles.

The second number affects the distribution of tick points.  An AI seach yielded the following:

"... controls the rate of change as the parameter approaches and leaves a key, respectively, expressed as parameter units per tick. " 

The value must be  positive and I have found the most significant values are between 0 and 1.

Here's my curve with values of -2, 1 for x and 2, 1 for y.

Here's the result for  -2, 0.1 for x and 2, 0.1 for y

The distribution of ticks here is also affected by the values of the "out" parameters for the preceding keyframe.

Please note that 4 control points (not two)  are required to define a cubic Bezier spline.  Or, two points plus the direction and magitude of the handles at the two points (which in essence defines the location of the third and fourth control vertex).

The distribution of the tick marks is controlled by the positioning of the interpolation points of the Bezier spline via uniformly incrementing the independent variable of the spline.

[849675273]

First of all, thank you very much for your response.

I roughly understand what you mean.But there is still one question that confuses me —— as demonstrated in your first image，(-5, 5) does indeed affect the length of the Bezier spline handles, but how is the value '5' calculated?

[849675273]

@leeminardi  First of all, thank you very much for your response.

I roughly understand what you mean.But there is still one question that confuses me  as demonstrated in your first image，(-5, 5) does indeed affect the length of the Bezier spline handles, but how is the value '5' calculated?

[leeminardi]

The hadle length 5 in the example is the distance from the first to the second control vertex for the start point of the Bezier spline.  For the end of the spline it's the distance from the third to the fourth control vertex.  In some CAD programs (e.g., AutoCAD) you don't have handles and you use the positioning of CVs to control the slope and instantaneous radius of curvature at the ends of a Bezier splne and the more advanced B-splines and NURBS.

Here's an example of a cubic Bezier spline in Excel with CVs at 0,0  0,10  10,10 and 10,0.

Here's a spline in Max with end points at 0,0 and 10,0, and handles that are vertical and 10 long (measured from the spline vertex to the handle end.

I've attached my Excel Bezier file if yuo would like to experiment with CV values and how they affect the shape of a Bezier spline.

[849675273]

thank you for the detailed Excel document. But this conclusion may not apply to the motion curve. i show you an example below。

there is a sphere，has 2 keys in frame 0 and 10

I have already marked the coordinates of the four control points.

This is its key information at frame 0. But 0.629 can't possibly be its length or slope or anything like that。

[leeminardi]

The out values for Y of 0.629  combined with the -0.004 for x yields the shown slope of about 90° for key 1.­  I don't know how the 0.629 is related to the handle lenght of about 10.  There's a scaling factor being applied but I don't know where it's coming from.  I'll give it some tought.

[MartinBeh]

Note the "Free Handle" option below the Normalize Time button - without this, the two tangents before/after seem to be "normalized" to the time range between two neighboring keys (e.g. if you have two keys ten frames apart, the value is multiplied/divided by ten if you check/uncheck "Free Handle").

So if you check that option, your value changes to something that looks like absolute values - maybe that is what you are after?

This page says:

"Free Handle

Used for automatically updating the length of the tangent handle. When this is turned off, the length of the tangent is at a fixed percentage from its neighboring key. As you move a key, the handles adjust to stay the same percentage away from the neighboring keys. When this is turned on, the handle lengths are based on time lengths."

[849675273]

Thank you for your response. I hadn't noticed this before. Checking this option will change the value of the second line in Key Info, but now I'm confused about the value of the first line.