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Original Unflip :

Original – horizontal flip:

Original vertical flip:

so i tried our own example, it kind of works, but not as expected

cd packages/core
yarn run example volumeAPI

When I try flippingH on Sagittal it flips but then I can't flip back. I confirm that there was a bug that you couldn't flipH on Sagittal at all, so it is progress I guess?

Axial (acquisition)

• FlipH and FlipV works (both ways)S

Sagittal

• FlipH works just once
• FlipV works

Coronal

• FlipV works just once
• FlipH works

Note: you can try scrolling to a slice other than the middle slice of the volume to see effects of the flip better, you can use

cornerstoneTools.utilities.scroll(viewport, {delta: 30})

I did some digging into this, I guess the correct implementation should do it based on viewRight and viewUp, and not the direction of the image itself, since that is basically what we mean by flipHorizontal and flipVertical. I tried it

 const { focalPoint, viewPlaneNormal, viewUp } = this.getCamera();

    const viewRight = vec3.create();
    vec3.cross(viewRight, viewPlaneNormal, viewUp);

    const center = focalPoint;
    let flipHTx, flipVTx;

    const transformToOriginTx = vtkMatrixBuilder
      .buildFromRadian()
      .identity()
      .translate(-center[0], -center[1], -center[2])
      .rotateFromDirections(viewRight, [1, 0, 0])
      .rotateFromDirections(viewUp, [0, 1, 0]);

    const transformBackFromOriginTx = vtkMatrixBuilder
      .buildFromRadian()
      .identity()
      .rotateFromDirections([0, 1, 0], viewUp)
      .rotateFromDirections([1, 0, 0], viewRight)
      .translate(center[0], center[1], center[2]);

    if (flipH) {
      this.flipHorizontal = flipHorizontal;
      flipHTx = vtkMatrixBuilder
        .buildFromRadian()
        .multiply(transformToOriginTx.getMatrix())
        .scale(-1, 1, 1)
        .multiply(transformBackFromOriginTx.getMatrix());
    }

    if (flipV) {
      this.flipVertical = flipVertical;
      flipVTx = vtkMatrixBuilder
        .buildFromRadian()
        .multiply(transformToOriginTx.getMatrix())
        .scale(1, -1, 1)
        .multiply(transformBackFromOriginTx.getMatrix());
    }

It works for flipHorizontal for all views (except oblique) but not for vertical.

I guess the main issue is that flipping happens at the actor matrix level, and actor matrix is agnostic to the camera view, so that is why some orientations it works and some don't (?)

I can dig more later

there is a feature definition issue : the flip is about flipping the original orientation.
typical use case is for XRay where depending on what you want to do, you may want to see left & right hand in the same orientation or opposite. ( for CT / MR, the use case, is the patient is in supine/prone position. but this resolve using the rotate tool - all acquisition I ever seen are head first. no feet first ).

this is the current implementation. so if your acquisition is AXIAL, and the view is SAGITAL, horizontal flip, exchanging left and right has no effect on the (sagital) view.

Using viewup + normal would be required if you want to achieve an engineer feature : flip view in any orientation. but in this case, there is a need for a large refactor to handle it correctly. for instance you flip image, then using the crosshair you tilt the view, and then if you flip, it's along another axis plane. so in the end, you cannot have a "flip" indicator.

#271 draft

can we close this in favor of recent merged PRs?

I'm closing this, please re-open if needed