When editing linear transformations, the buttons work as follows:

• Left Button: Translation of current section.
  Press and hold the button and move the mouse to drag the section to the desired location relative to the reference section.
• Middle Button: Rotation of current section.
  Position the mouse near the edge of the image, press and hold the button, and move the mouse tangentially around the center of rotation (yellow star). The current section will rotate by a corresponding amount relative to the reference section.
• Right Button: Stretch of current section.
  Position the mouse near the edge of the image along the desired axis of stretch. Press and hold the button, and move the mouse radially away from or toward the center of rotation (yellow star). The current section will stretch or compress by a corresponding amount along the radial axis, relative to the reference section. Stretch behaves differently with a second fixed point (red star). In this case, position the mouse far from the line between the center of rotation and the fixed point, and move it in any direction. The image will stretch and skew by a corresponding amount.
• [Shift] + Right Button: Magnification of current section.
  Position the mouse near the edge of the image, press and hold the Shift key, press and hold the mouse button, and move the mouse radially away from or toward the center of rotation. The current section will expand or shrink by a corresponding amount relative to the reference section.
• [Ctrl] + Left Button: Shift zoomed-up image in window.
  When the whole image does not fit in the window, press and hold the Ctrl key, press and hold the mouse button, and move the mouse to drag the image to the desired position in the window.
• [Ctrl] + Middle Button: Move the center of rotation and stretch.
  Position the mouse at the desired center of rotation, press and hold the Ctrl key, and click the mouse button to specify the new position.
• [Ctrl] + Right Button: Toggle second fixed point for stretch. Position the mouse at the desired fixed point, press and hold the Ctrl key, and click the mouse button to specify the fixed point. The fixed point is turned off by clicking again.

When adding or editing warping control points, the buttons work as follows:

• Left Button: Translate image around control point, or select current point.
  Press and hold the button and move the mouse to drag the image locally to the desired location relative to the reference section. Click the button near a desired control point to make that point be the current point.
• Middle Button: Add control point.
  Click the button at a desired location to add a control point there.
• Right Button: Move control point.
  Click the button at a desired location to move the current control point there. This does not change the shift between images at that point.
• [Shift] + Left Button: Select current point.
  Click the button near a desired control point to make that point be the current point.
• [Ctrl] + Left Button: Shift zoomed-up image in window.
  When the whole image does not fit in the window, press and hold the Ctrl key, press and hold the mouse button, and move the mouse to drag the image to the desired position in the window.