Review the eraser tool

[lucasrla]

I've never really tested the eraser tool thoroughly. So I won't be surprised at all that remarks has issues with it...

Ref #63 (comment) and #63 (comment).

[Azeirah]

I made a notebook (on ReMarkable version beta 3.3) that looks at the eraser: eraser testing.zip

In it, there are three squares and three lines of text.

1. The first of either should be visible, no eraser applied whatsoever

2. The second is erased with the back of the ReMarkable physical pen

3. The third is erased with the eraser tool

In neither cases does (2) the eraser at the back of the pen fail, but what's really strange here is that (3) only the text has visible eraser marks when the tool is used.

[Azeirah]

Here's a more carefully constructed file. Oddly enough it has fewer obvious issues. I took a photo with my phone before and after erasing, to ensure I didn't forget copying a drawing before erasing it.

What you can see in the remarks output is that everything is erased as expected. However, in the first vertical table bar, there are two holes in the 3rd and 4th column (next to "hello" and the scribbles underneath it). Weird!

Before:

After:

Remarks' output:

The notebook:

testing erasers.zip

[Azeirah]

I made a notebook (on ReMarkable version beta 3.3) that looks at the eraser: eraser testing.zip

In it, there are three squares and three lines of text.

1. The first of either should be visible, no eraser applied whatsoever

2. The second is erased with the back of the ReMarkable physical pen

3. The third is erased with the eraser tool

In neither cases does (2) the eraser at the back of the pen fail, but what's really strange here is that (3) only the text has visible eraser marks when the tool is used.

I found that the color codes of the erasers are incorrect. Two of them have color-code 0, which is black. The other one has color-code 2, which is white (correct)

I'm not sure why. I suspect we can safely override the eraser's color with WHITE in all cases. I have a slight suspicion that ReMarkable has a global selected_tool instance, and sets properties on that instance given what you do in the UI.

So if you have an eraser, then select a tool and put the color to black and go back to the eraser, the eraser could have a color-code of black, even though this value is meaningless for the eraser. This is just a suspicion though.

[Azeirah]

Remarks' output:

The notebook:

testing erasers.zip

This issue occurs because the calculation for the eraser width produces very large values for certain w.

    elif tool == "Eraser":
        w = 1280 * w * w - 4800 * w + 4510
        # cc = 2

I'm not sure where these values come from, but with the input value of w=2.4, the computed eraser width is over 360. This is obviously far too large. I'm not sure what a good value would be, but this calculation is clearly off.

>>> 1280 * w * w - 4800 * w + 4510
362.7999999999993