Same margin before and after a list between paragraphs?

[aried3r]

Hey and thanks for this gem!

I'm currently playing around with this gem and was wondering if there is a way to have the same bottom and top margin/padding in a list surrounded by paragraphs?

<p>Top paragraph</p>
<!-- Add a margin here -->
<ul>
  <li><p>A</p></li>
  <li><p>list</p></li>
  <li><p>with</p></li>
  <li><p>elements</p></li>
</ul>
<!-- Add same margin here -->
<p>Bottom Paragraph</p>

Expected result (HTML rendered in a browser)

Actual result

BASE_LINE_GRID = 13

markup_options = {
    text: {
        leading: BASE_LINE_GRID - font.height_at(8.5),
        # Default margin_bottom seems like a sensible default, let's keep
        # it for now.
        # margin_bottom: 0 # Margin after each <p>, <ol>, <ul> or <table>
    },
    list: {
        vertical_margin: 0, # margin at the top and the bottom of the list
        bullet: {
            margin: 0 # Margin before bullet
        },
        content: {
            leading: BASE_LINE_GRID - font.height_at(8.5), # Vertical padding between list items
            margin: 4 # Between bullet and content
        }
    }
}

I assume what I'm seeing here is the margin_bottom of the "Top Paragraph" <p> + an additional padding/margin on top of the list (although vertical_margin is 0).

If I change it text: { margin_bottom: 0 } of course the margins at the bottom of the first <p> are gone, and so is the margin at the bottom of the <ul>. However there is still a margin before the list and I'm not sure where it's coming from.

Even when I set everything (well, I guess not everything otherwise it'd be gone) to 0, there's still a distance between the top paragraph and the bottom one.

markup_options = {
    text: {
        leading: 0
        margin_bottom: 0 # Margin after each <p>, <ol>, <ul> or <table>
    },
    list: {
        vertical_margin: 0, # margin at the top and the bottom of the list
        bullet: {
            margin: 0 # Margin before bullet
        },
        content: {
            leading: 0 # Vertical padding between list items
            margin: 4 # Between bullet and content
        }
    }
}

[codez]

I found an unexpected move_down in the code of prawn table, which is used to render lists. Could you try the branch adjust_list_gaps with your example to see if it fixes your issue?

[aried3r]

Hey! Thanks for the quick reply. It seems that it doesn't fix the issue. I dug around a bit more (and hopefully don't confuse the screenshots), and I'm not quite sure which values get mixed up.

This is with all leadings set to 0. That definitely doesn't seem correct to me.

Thats with [:text][:leading] set properly.

This, IIRC, is with [:text][:leading] set to 0, and [:list][:leading] set properly.

Same as above but without borders to see what it looks like.

Here's two with horizontal lines being drawn before and after the text and borders around the list.
[:text][:leading] is 0, [:list][:leading] is correctly set, [:text][:margin_bottom] is 0, [:list][:vertical_margin] is 0.

And once without the table borders.

Sorry, that it's a bit messy, I was just quickly playing around with it. I should probably at this point just write a test PDF.

Anyway, prawn_list_gap in your branch is 1.8062500000000001 in my case which isn't much (btw, we could use move_up instead of move_down with a negative number). So I think it's a case where the leading of text and the leading of lists are somehow interfering, but I might be wrong. WDYT?

[codez]

Thanks for your analysis. Are you actually using a special font or is this the standard Helvetica in your example? This really seems to be some font spacing issue depending on descenders, ascenders and line gaps. Unfortunately, I am not really an expert in this field. Probably some more digging in the Prawn/Prawn-Table source code would be necessary.

There are various specs to start from. I used

prawn-markup/spec/prawn/markup/processor/lists_spec.rb

Line 176 in 631e6b4

it 'creates an unordered list' do

to play around. Inserting lookatit calls after processor.parse lines will directly open the generated PDF on Linux or Mac when running the specs.

[aried3r]

Are you actually using a special font or is this the standard Helvetica in your example?

I'm using "Gilroy", here's the same with Helvetica:
[:text][:leading] = 0, [:text][:margin_bottom] = 0, [:list][:leading] = 13 - font.height_at(8.5) (13 is the height of our lines)

[aried3r]

Ok, a more complete example:

BASE_LINE_GRID = 13

markup_options = {
    text: {
        font: 'Helvetica',
        size: 8.5,
        leading: BASE_LINE_GRID - font.height_at(8.5)
        # margin_bottom: 0 # Margin after each <p>, <ol>, <ul> or <table>
    },
    list: {
        vertical_margin: 0, # margin at the top and the bottom of the list
        bullet: {
            margin: 0 # Margin before bullet
        },
        content: {
            leading: BASE_LINE_GRID - font.height_at(8.5), # Vertical padding between list items
            margin: 4 # Between bullet and content
        }
    }
}

And I added another pdf.move_up(text_leading * 2) to your pdf.move_down(-prawn_list_gap). I'm not sure if that should be something else like text_leading + list_leading (list_leading doesn't exist yet) instead. Have to think about it some more.

But this is the result:

As you can see, I have quite sophisticated graphics skills. The lines almost line up, haha.

Edit: Found this regarding the gap they add, prawnpdf/prawn#539

[codez]

I guess I found the issue. The problem seems to be that the move_down in Prawn::Table::Cell::Text#draw_content and the used with_font do not use the actual cell's font size. So our prawn_list_gap is calculated from the cell font size, the one used in draw_content from the document font size. This also affects regular tables and is well visible when using a much larger font size in cells, where the vertical alignment is quite out of place.

Probably we should open an issue in prawn-table?

[codez]

Created prawnpdf/prawn-table#120.

Considering the last commit to the prawn-table code was 4 years ago, I will fix it here anyways.

[codez]

Pushed a new commit to https://github.com/puzzle/prawn-markup/tree/adjust_list_gaps

[codez]

@aried3r did you get a chance to test the changes? If everything is ok, I will cut a new version of the gem.

[aried3r]

Hey! So far I haven't, but I hope to take a closer look either tomorrow or beginning of next week.

Thanks for your work so far!

[aried3r]

I had a chance to test your changes, it seems to work! I think the move_up is not technically correct (see: prawnpdf/prawn#539, texts are not centered anymore within their cells), but it seems that way we actually get the result we expect, equal margins on top and bottom.

Result:

With table borders:

[codez]

Great, I'm about to release a new version.

[aried3r]

Awesome, thank you for your quick response!