# pushTransform method Null safety

- Matrix4 transform

Pushes a new transform matrix that is to be applied to all future HitTestEntrys added via add until it is removed via popTransform.

This method is only to be used by subclasses, which must provide coordinate space specific public wrappers around this function for their users (see BoxHitTestResult.addWithPaintTransform for such an example).

The provided `transform`

matrix should describe how to transform
PointerEvents from the coordinate space of the method caller to the
coordinate space of its children. In most cases `transform`

is derived
from running the inverted result of RenderObject.applyPaintTransform
through PointerEvent.removePerspectiveTransform to remove
the perspective component.

If the provided `transform`

is a translation matrix, it is much faster
to use pushOffset with the translation offset instead.

HitTestables need to call this method indirectly through a convenience
method defined on a subclass before hit testing a child that does not
have the same origin as the parent. After hit testing the child,
popTransform has to be called to remove the child-specific `transform`

.

See also:

- pushOffset, which is similar to pushTransform but is limited to translations, and is faster in such cases.
- BoxHitTestResult.addWithPaintTransform, which is a public wrapper around this function for hit testing on RenderBoxs.

## Implementation

```
@protected
void pushTransform(Matrix4 transform) {
assert(transform != null);
assert(
_debugVectorMoreOrLessEquals(transform.getRow(2), Vector4(0, 0, 1, 0)) &&
_debugVectorMoreOrLessEquals(transform.getColumn(2), Vector4(0, 0, 1, 0)),
'The third row and third column of a transform matrix for pointer '
'events must be Vector4(0, 0, 1, 0) to ensure that a transformed '
'point is directly under the pointing device. Did you forget to run the paint '
'matrix through PointerEvent.removePerspectiveTransform? '
'The provided matrix is:\n$transform',
);
_localTransforms.add(_MatrixTransformPart(transform));
}
```