How to use the fab style diamond?

How to use diamond style for fab + bottom app bar? In the sketch files on the website https://material.io/tools/theme-editor/ there are such styles fab:

Looked at all possible styles and tags...

Props to Gabriele Mariotti. I used his code and changed it a little bit to give the rounded look to bottom app bar like in the original question.

Firstly for the FAB I gave it rounded corners and rotated it 45 degrees like this:

XML code for fab:

<com.google.android.material.floatingactionbutton.FloatingActionButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/fabHome"
        android:rotation="45"
        app:layout_anchor="@id/bottomBarHome"
        app:shapeAppearanceOverlay="@style/FabDiamondOverlay"/>

The FabDiamondOverlay is:

<style name="FabDiamondOverlay" parent="">
    <item name="cornerFamily">rounded</item>
    <item name="cornerSize">15%</item>
</style>

which gives the resulting FAB:

Now for the bottom bar XML:

<com.google.android.material.bottomappbar.BottomAppBar
        android:id="@+id/bottomBarHome"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:backgroundTint="@color/grey"
        app:fabCradleMargin="20dp"
        app:fabCradleVerticalOffset="5dp"
        android:layout_gravity="bottom" />

and this code in OnCreate method to give bottom app bar a custom look:

    BottomAppBar bar = findViewById(R.id.bottomBarHome);

    BottomAppBarTopEdgeTreatment topEdge = new BottomAppBarCutCornersTopEdge(
            bar.getFabCradleMargin(),
            bar.getFabCradleRoundedCornerRadius(),
            bar.getCradleVerticalOffset());

    MaterialShapeDrawable bottomBarBackground = (MaterialShapeDrawable) bar.getBackground();
    bottomBarBackground.setShapeAppearanceModel(
            bottomBarBackground.getShapeAppearanceModel()
                    .toBuilder()
                    .setTopRightCorner(CornerFamily.ROUNDED,75)
                    .setTopLeftCorner(CornerFamily.ROUNDED,75)
                    .setTopEdge(topEdge)
                    .build());

Where BottomAppBarCutCornersTopEdge is by modifying Gabrielle's code: Source

@Override
    @SuppressWarnings("RestrictTo")
    public void getEdgePath(float length, float center, float interpolation, ShapePath shapePath) {
        float fabDiameter = getFabDiameter();
        if (fabDiameter == 0) {
            shapePath.lineTo(length, 0);
            return;
        }

        float diamondSize = fabDiameter / 2f;
        float middle = center + getHorizontalOffset();

        float verticalOffsetRatio = cradleVerticalOffset / diamondSize;
        if (verticalOffsetRatio >= 1.0f) {
            shapePath.lineTo(length, 0);
            return;
        }

        float barLeftVertex = middle - (fabMargin + diamondSize - cradleVerticalOffset);
        float barRightVertex = middle + (fabMargin + diamondSize - cradleVerticalOffset);
        float depth = (diamondSize - cradleVerticalOffset + fabMargin) * interpolation;

        float heightArc = 25;
        float widthArc = 25;

        shapePath.lineTo(barLeftVertex, 0);

        shapePath.lineTo(middle-widthArc, depth-heightArc);

        shapePath.addArc(middle-widthArc-10, 35, middle+widthArc+10, depth-15, 135, -83);

        shapePath.lineTo(middle+widthArc, depth-heightArc);
        shapePath.lineTo(barRightVertex, 0);

        shapePath.lineTo(length, 0);
    }

The values here were decided with hit and trial. I couldn't understand what every variable did and there seems to be really less documentation about it. But it gets the job done! Here is the final result: