Increase usability by adding reading ruler to Evince

Some people are experiencing trouble when reading from their computer screen. From the computer screen they easily skip lines or half way a line of text they continue reading at another line. It could be that people suffering from dyslexia are more likely to have these problems, but I am not sure about this. Anyway, I think a simple feature can be added to the PDF reader to help these people: a reading ruler. A reading ruler is a horizontal line that is being rendered over the PDF page. The vertical position of the line can be controlled by the position of the mouse pointer.
Below you can see different mockups that I made.
In the first mockup there is only a line below the line of text the user is reading.
In the second mockup there is a partially transparent overlay below the ruler. The idea behind the overlay is that the text that the user did not read yet is less visible and therefore less distracting for the user. The overlay is partially transparent to make sure that the text below it is not completely hidden, so the user still has an overview of the contents of the rest of the page.
In the third mockup there is also and overlay, but it becomes gradually more transparent in the lower region below the ruler. The reason for using a gradient is that we only need to hide the space below the ruler that is close to the ruler, because when reading the eyes are focused on this region.