Distorting the Output with the Warping module

The Warping module is a feature of the Output Setup. It is there to let you distort an output to adjust it precisely on your projection surface.

To use the warping feature, your output needs to be in "Setup" mode (the more advanced one, accessible fromor Output → Setup...).

There are two warping types: Perspective and Points and both can be combined.

Perspective warping

Perspective warping allows you to adjust the corners of a Screen to skew its rendering in the output while keeping the perspective effect. For instance it can be used to correct the shape of the output and make it rectangular if your projector is not perpendicular to the projection surface (like a keystone correction).

1. Select a Screen.
2. On the right, select "Perspective" for the Warping type (it's the default one).
3. Select a corner of the screen in the Screens setup area.
4. Move this corner either with your mouse pointer, the arrow keys (to move precisely pixel by pixel) or by changing its coordinates in the Warping section.
5. Optional: to find your pointer more easily in the output, you can check "Show geometry in output" et "Show cursor in output" in order to, respectively, show the warping points and the cursor in the output rendering. The appearance of the cursor can be edited in Edit → Preferences... → Output → Output Setup cursor. (as of 2.13.2)

As shown in the screenshot of the output destination just above, the rendering is distorted to correspond to the deformations you have applied to the Screen in the Output Setup.

Note: the warping distortion only affects the output rendering, it is not reflected on the Canvas in the work area or in the output setup window.

Points warping

Accessing Points warping

Points warping allows you to distort only an area of the output, for instance to compensate for asperities on the projection surface. Imagine stretching a piece of cloth to change its shape—this is akin to warping.

1. Select a screen.
2. On the right, select "Points" for the Warping type.
3. Adjust the number of Subdivisions if needed (from 1 to 15 on each axis).
4. Select a point on the warping grid of the screen in the Screens setup area.
5. Move this corner either with your mouse pointer or with the arrow keys (to move precisely pixel by pixel).
6. Optional: to find your pointer more easily in the output, you can check "Show geometry in output" et "Show cursor in output" in order to, respectively, show the warping points and the cursor in the output rendering. The appearance of the cursor can be edited in Edit → Preferences... → Output → Output Setup cursor. (as of 2.13.2)

As shown in the screenshot of the output destination just above, the rendering is distorted to correspond to the deformations you have applied to the Screen in the Output Setup.

Note: the warping distortion only affects the output rendering, it is not reflected on the Canvas in the work area or in the output setup window.

Using Bézier (2.13)

There are 2 modes for points:

• Linear: this is the default mode. As you can see from the grid created by the rows and columns, the lines connecting each point to its neighbors are straight.
• Bézier: this mode keeps the same points, but adds two Bézier tangents to each of them so that you can curve the warping. A tangent is made of 1 or 2 control handles: each point has as many as there are points it is linked to (e.g. a corner only has 2 control handles while a point in the middle has 4.)
  When a point or one of its handles is selected, you can change the type of both associated tangents with the “Handles” toggle on the right. By default handles are Asymmetrical (both handles in a tangent form a straight line but they don't have to be the same length), but this can be switched to Disconnected (both handles are completely independent).
  

These modes are mutually exclusive. Either all points of the Screen have handles or all don’t.

Depending on the curvature you’re trying to reach, a few tricks can help you in addition:

• “Make circle” button (only in Bézier): this option adapts the warping points so that the Screen is turned into a convex dome. Handy if you’re projecting on a sphere!
  Note: in this case the rows & columns are reduced to 1, but you can still change this afterwards or revert back with [CTRL/Cmd + Z]
• Changing Rows & Columns follow the bend: while it’s usually better to know how many points you need from the get-go, it can be time-saving to start with a low number when adjusting a curve. Indeed, with few points, you can start roughly placing them on the curve and then increase the numbers progressively to gain control points. These new points will follow the curvature you have set as best they can, without having to adjust them independently.
  

Comparing and combining Perspective and Points warping

Unlike Perspective adjustments, the deformations in Points warping evenly stretch the rendering of the Screen. Here’s a comparison:

However, they adapt to those in the Perspective type, so both transformations can be used in combination.

Note: if you use the reset button in one mode ("Reset corners" for Perspective and "Reset points" for Points), it only resets the deformations made for this particular type of warping.