Adobe Photoshop CC 2014 v.14.xx - Manual (Page 27)

Warp mode
2. Manipulate perspective in one of the several available ways:
Move around the corners of the quads (pins) as appropriate. For example, you can adjust the perspective of this image, such that the two
sides of the building exhibit foreshortening in equal measures. The resulting perspective would approximate a direct view of the building from
a corner.
Adjusting the perspective, such that the two sides of the building are equally foreshortened
Shift-click an individual edge of a quad to straighten it and keep it straight during further perspective manipulation. Such a straightened edge
is highlighted in yellow in the Warp mode. You can manipulate the corners of the quads (pins) for finer control while adjusting perspective.
Shift-click to straighten an individual edge of a quad and keep it straight during further perspective manipulation. The rightmost selected edge in
this image is highlighted in yellow.
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