The Mirror plugin splits the image along a line, an axis, and reflects one side onto the other. When the Enable Reflection Center option is checked you can move the position of this axis, using X% and/or Y% slider and/or textbox:X% for the horizontal position andY% for the vertical position. Mainly in the Mirror effect there are 2 cases: with or without the Enable Reflection Center checked.
When the Enable Reflection Center option is UNCHECKED, the used reflection is on the center of the image (i.e. X50%, Y50%) and the options about Reflection Center, X%and Y%, are disabled (grayed). The Horizontal option reflects the left side of the image on the right. If the Swap LEFT-RIGHT side option is checked then the right side to the left will be reflected. The Vertical option reflects the top on the bottom. If the Swap TOP-BOTTOM side option is checked then the bottom to the top will be reflected. There are special combinations when both Horizontal and Vertical checkboxes are enabled (and Enable Reflection Center is always UNchecked, of course). You can see those combinations in the figure 10.51.
When the Enable Reflection Center option is CHECKED the options about Reflection Center, this is.X% and Y%, are enabled, and the two Swap ... side options are disabled and hidden. These two Swap ... side are disabled because theX% and Y% allow the swap side feature automatically. TheX% and Y% positions move the center of the reflection to fit to the User's need.
The CINELERRA-GG Community, 2021