I am using the hatched area (style 3144) to represent the represent the errors.
And I want to have the same spaces between lines in two pads of different size.
By default, they are not.
I’ve tried gStyle->SetHatchesSpacing but it doesn’t work for me.
The hatches greater than 3025 are in fact not fill patterns but lines drawn by ROOT graphics.That’s why you can change spacing and line width. It may well be that some effects similar to what you describe can appear. This would require a closer look to see why… To make sure you have invariant hatching choose the pattern in the top 25 ones shown on this table.
indeed the line spacing depends on the pad size because these pattern are drawn using normal line. You can see the same effect if you grow and shrink the canvas. The line spacing adjust according to the canvas size. That something special to these patterns and might be useful in some cases.