ScaleTransform transforms non-linearly

Answer 1

Any reason why you are not using ResizeContainer.RenderTransfrom instead of ResizeContainer.LayoutTransform? I.e. use

ResizeContainer.LayoutTransform = scale;

If you want the scale to be linear I think you should use

double scaler = 1 - diff / ResizeContainer.ActualWidth;

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EDIT:

There is a bug in the code that causes the scaled control to "jump" in size if you try to resize more than once. I suggest you do the following:

Add a RenderTransform to your ResizeContainer grid:

<Grid.RenderTransform>
    <ScaleTransform x:Name="transform" ScaleX="1" ScaleY="1" />
</Grid.RenderTransform>

Change the code in your MouseMove event handler to the following:

if (bottomResize)
{
    double newBtmX = e.GetPosition(this).X;
    double scaler = -(initBtmX - newBtmX) / grid1.ActualWidth;
    initBtmX = newBtmX;

    transform.ScaleX += scaler;
    transform.ScaleY += scaler;
}

This way you change the scale by whatever small amount the mouse has moved while dragging. All child controls within the grid should scale as well.