# Mewa User's Guide/Animating parameters with Curve Editor
## What is the Curve Editor

The curve editor is the heart of any animation, its a very intuitive graphical tool where you can model the behaviour of one or more parameters over time as a curve, e.g. to animate an object in a video we change the position of the object.
The shows and hides the curve editor.
In the node graph each node has its own parameters shown at parameters window where they can be modified. To see the node's parameters just click the node parameters button to make parameters window pop up.
Every parameter has an input text box where the parameter value is shown. The shown value is always the parameter value at the current play frame. The play frame number is shown in the timeline and pointed by the play-head. If a curve is associated to the parameter, the parameter value will show the curve value at the current play frame.
Pressing down on the input box and draging makes the parameter value change proportionally to the dragging movement. This is how parameter values are adjusted.
Some parameters show a progress line just above the input box (see node parameter image on the right). That's because that parameter limits its value within a range. As the parameter value changes the progress line above the input box indicates it's value relative to it's min and max values.
To animate a parameter value throught time we use a curve. A curve can be modelled point by point and can be reused in any parameter.
Parameters have a curve button. Clicking the curve button shows a menu with a list of available curves and the option to create a new curve.
You can associate a parameter to an existing curve by clicking a curve from the curve button menu. To create a new curve click the new curve... option, the first option in the curve button menu. The created curve will be shown in the curve editor as a flat line, which means constant value. The name of the created curve contains the node name followed by the parameter name.

## The Curve Editor window

Curves are modelled in the curve editor. To open or close the curve editor toggle the button Curve Editor located at the bottom left of the application window.
To see the list all the available curves toggle the curve list view button located on the top left of the curve editor window. The curve list view is shown on the left of the curve editor window.
A curve can have as many points as you need and each point has an interpolation method that can choose.
As a curve is modified it's changes are propagated through all the parameters using the modified curve. This means we can visualize the result at the output window while changing a curve.

## Navigating the Curve Editor
### Fit in view

The Fit in view button zooms the view to fit the selected points on the current view. If there are no points selected the Fit in view button will fit all points of the current selected curves.

### Zoom and Pan

You may navigate the Curve Editor space by using the Middle Mouse button to pan and the mouse wheel to zoom.

## Editing curves
### Creating an new curve

The new curve button creates a new curve with 1 point. The point is created at the frame number indicated by the play head.

### Working with curve points

Manipulating the curve to obtain the desired curve is easily achieved by moving and creating new points. To move a point use the left mouse button to drag the point to a new position position. It's also possible to move a selection of points.
There are several ways to select points in a curve, the most usual way is by is clicking on the point you wish to select. To select multiple points you can
* Use the rubber band: press an empty area and drag to resize the rubber band rectangle. All points under the rubber band rectangle will be selected.
* Hold shift key while clicking on the points to select.
Left mouse clicking in a empty area clears any selection of points.
To add points,
* click over a curve line, both curve line or extrapolation line. Note that the mouse cursor changes it's icon to a point finger icon to indicate that the mouse is over a line and if you click a point will be created.
* or use the context menu, right-mouse click and choose New Point.

### Deleting points

To delete points select one or more points and:
* click .
* or, press delete key,
* or, right-click over one of the selected points to open the context menu and choose delete.

### Curve interpolation

Interpolation defines the shape of a curve between points. At the top of the curve editor is the interpolation buttons group which offers a list of pre-determined interpolation options.
The 4 interpolation options are:
* Linear interpolation
* Ease in interpolation
* Ease out interpolation
* Ease in&out interpolation
To change the interpolation between points, select one or more points,
* Click one of the interpolation buttons
* right click on a point to open the context menu and select an interpolation mode

### Custom interpolation

Custom interpolation can also be referenced as cubic interpolation as it provides cubic handlers to adjust a cubic interpolation curve.
At the top of the curve editor window is the show cubic handlers switch:
To use it select one or more points and choose to show the cubic handlers.
When cusrom interpolation is chosen 2 tangent controls appear, also called handlers. Use these handlers to adjust the cubic interpolation to a desired form.

### Curve Extrapolation

Extrapolation is the region of the curve outide the movable points. Extrapolation defines the shape of an animation curve before the first point and after the last point. The default extrapolation method is Constant extrapolation, which simply holds the value steady. It looks as an horizontal line.

### Copy and paste points

* Select the points to copy and press Ctrl+C,
* move the play head to the frame which the copied points will be inserted,
* press Ctrl+V to paste.
Note that the curve's section after the play head is shifted to the right to give space for the new pasted points.

## Bar view

At the top of the curve editor window is the bar or curves switch button .
The bar view displays curves as horizontal bars, which is very usefull when we only want to adust curve points horizontally (time scale) and not change its value.
Note that all footage nodes are presented at the top of the bar view, not as curves but as horizontal bars.
All footage nodes have inherently a linear curve where the value of the curve is the frame number in the footage file. To make it easier for users to position footage nodes in time as do some holding and trimming adjustments, footage time bars are created for every footage node.

## Adjust footage timing

The bar view allows users to arrange the timing of footage nodes. Each footage node has an instance in the bar view displayed as horizontal bar.
The duration of a footage node is determined by the length of the bar. Where the footage starts and ends is represented by the begin and end of the horizontal bar. To adjust the start time of a footage node just move the correspondent footage bar. Footage bars only move horizontally.

### Holding and trimming

Holding and trimming are techniques to change the footage node duration. Trimming consists of cutting the last frames from the original footage node, and holding is used to extend the footage node with the last frame.
Footage bars have 2 handlers, in the form of arrows, at their ends. These handlers are used to adjust the length of the footage. You can trim frames off of the beginning or the end of a footage by adjusting the left or right handler.
To increase the duration of a clip, by holding the last frame, drag the right handle to the right. The footage duration extends as you pull the handle to the right or left. Note that the original footage size has a different color than trimmed/hold frames at the bar ends.
If the left handler at the beginning of the bar is dragged to the left the newly extended area of the footage, in a lighter color, represents the duration of the footage that has been expanded by freezing the first frame.
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