CornerPositioner

**What CornerPositioner does.** This tool warps a 2D image to four points, pinning a flat insert to a quadrilateral such as a screen, sign, door or display. The operation does not create a 3D scene or reconstruct the photographed camera.

**Two mappings, not two quality presets.** `Bi-Linear` interpolates the quadrilateral in 2D, whereas `Perspective` applies a planar perspective projection. Both use exactly the same four corner positions, but internal straight lines and proportions may differ.

**When Perspective fits.** A rectangular real-world plane filmed obliquely usually benefits from perspective interpolation: receding edges and interior lines behave more naturally. This does not mean the tool solves lens distortion, camera movement or a tracking path.

**When Bi-Linear helps.** This mode is useful for particular stylized deformations, compatibility with an existing comp, and controlled A/B checks. It need not preserve interior straight lines like a planar perspective mapping: use a checker grid for comparison.

**Four independent corner positions.** `Top Left`, `Top Right`, `Bottom Left` and `Bottom Right` each have X/Y coordinates. In the usual normalized Fusion frame, left is near X=0, right near X=1, bottom has smaller Y and top has larger Y.

**Read the original Inspector accurately.** The captured example shows Top Left=(0.1, 0.9), Top Right=(0.9, 1.0), Bottom Left=(0.0, 0.3), Bottom Right=(1.0, 0.1). These are example point positions, not a recommended preset for all shots.

**Independent Offset X and Offset Y.** Every corner provides additional local X/Y displacement. After binding the main position to a tracked path, offsets help align the path reference with the actual screen corner without replacing the source animation.

**Reset Offsets is not Reset All.** The button clears additional offset values, not the primary four-corner placement, tracker data or the whole node. Do not treat it as a universal undo: record the current offset values before resetting a tuned setup.

**Corner order is critical.** Swapping, for instance, top-right and bottom-left may cross the quadrilateral and cause foldover, mirrored portions or unpredictable sampling. Validate orientation with a numbered checker image or asymmetric letters.

**Geometry before integration.** The mapped insert usually enters `Merge.Foreground` over the original plate. Brightness, blur, grain, reflection and foreground occlusion still require separate attention: CornerPositioner does not light or grade the inserted surface.

**Effect Mask is a separate blue socket.** Fusion 21 documents an orange image `Input` and a blue `Effect Mask` connector. The mask limits application of the already calculated warp; it is not a second image or a substitute for foreground cutouts before Merge.

**Tracking is not built in.** CornerPositioner does not inspect motion across frames. For a moving plane, animate corner coordinates, link them to Paths/Trackers, or perform PlanarTracker analysis first and apply its saved motion via PlanarTransform afterward.

**A separate PlanarTransform after CornerPositioner.** The documented approach corner-pins an insert on the tracking reference frame, then applies stored planar motion through PlanarTransform. This is not a magical direct graph wire from Tracker to all four corners; the analysis must exist first.

**Keyframes and modifiers.** The corner positions can be animated or linked to standard path/tracker modifiers in Fusion. If a tracker follows a nearby feature rather than the exact edge, use a controlled offset before rewriting the whole animated corner curve.

**Four points cannot replace lens modeling.** An original screen photographed with a wide-angle lens may have curved edges that no planar quadrilateral reproduces exactly. Solve lens distortion separately or use an appropriate distortion/undistortion sandwich around the composite.

**Resampling and softness.** Strong warps and repeated geometric stages resample image pixels. Avoid unnecessary PerspectivePositioner→CornerPositioner round trips: these operations are not guaranteed to concatenate and may soften fine text and UI details.

**Alpha and transparent borders.** Inspect the insert’s existing alpha and newly exposed regions after corner pinning. Merge operation, matte coverage, premultiplication and final alpha need a live pixel-level check; a controls screenshot alone cannot certify every edge.

**Static screen workflow.** Mark four screen corners in the photographed plate, start with an asymmetric test grid, use Perspective mapping and then Merge the result over the plate. Judge edge fit in context rather than looking at the insert alone.

**Moving footage checks.** Make sure the tracker analyzed the photographed plate and stored meaningful planar motion. Review at least the beginning, middle and end of the shot, plus any foreground occlusion. A single perfectly matching still frame proves little.

**Verification boundary.** The project has one original Controls capture, while the image/mask sockets are documented in the Fusion manual. Teaching graphs are type-checked statically; rendered warps, mask behavior and sharpness in Resolve 21 still require native evidence.