In the SpriteEffects palette, in the Effects list, a symbol to the left of each effect name shows the state of the selection mask for the effect. You can click the symbol to toggle the mask on () and off ().
An active selection mask defines a selection for an effect. The selection will include objects, not empty space. The mask can preserve transparent areas, such as empty space in a group object, and space between text characters.
When the selection mask is on, the effect is based on the selection area. When the selection mask is off, the effect is based on the entire bounding box area; e.g., if you apply the Add Noise command to a circle, the selection includes only the circle, so the noise affects only the circle if the mask is on. If the mask is off, the noise appears in the entire bounding box area.
For a built-in effect, Canvas X Draw uses the best selection mask setting. For third-party effects, you might need to change the mask setting for the best results.
Blur effects usually require the selection mask to be off, so the blur can extend beyond the outline of an object. Other effects look best when they are based on a selection; e.g., a flame effect will cover an entire bounding box if the selection mask is off. If the mask is on, flames will rise from just the objects or text characters in the selection. This does not mean that flames can’t rise above the selection, just that the effect will be based on the selection, not the entire bounding box.
When you edit the settings for an effect, Canvas X Draw displays a border on the selection, the same as the selection border that appears in images.