Improve support for LaTeX multi-line formulas

## Details

As a follow up from:
#6,
when LaTeX formulas are multi-line we end up showing the formula
on the first line and not overwriting the actual contents, which
does not look great.

Rather than attempting to overlay the formula as before, use
virtual lines above the text itself.

This is different from the standard rendering experience of an overlay
but I think is generally a nicer experience.

This will have some issues if the inline LaTeX is surrounded by other
text, which seems like an okay trade off.

Author: MeanderingProgrammer

demo/demo.gif

@@ -40,3 +40,8 @@ if __name__ == "__main__":
 | Row 3 Item 1 | Row 3 Item 2 |
 
 $\sqrt{3x-1}+(1+x)^2$
+
+$$
+f(x,y) = x + \sqrt{y}
+f(x,y) = \sqrt{y} + \frac{x^2}{4y}
+$$

demo/sample.md

@@ -1,7 +1,9 @@
-demo:
+default_zoom := '10'
+
+demo zoom=default_zoom:
     rm -f demo/demo.gif
     python demo/record.py \
-      --zoom 10 \
+      --zoom {{zoom}} \
       --file demo/sample.md \
       --cast demo.cast
     # https://docs.asciinema.org/manual/agg/usage/

justfile

@@ -121,19 +121,18 @@ M.latex = function(root)
     end
 
     local latex = vim.treesitter.get_node_text(root, 0)
-    local expression = vim.trim(vim.fn.system('latex2text', latex))
-    local extra_space = vim.fn.strdisplaywidth(latex) - vim.fn.strdisplaywidth(expression)
-    if extra_space < 0 then
-        return
-    end
+    local raw_expression = vim.fn.system('latex2text', latex)
+    local expressions = vim.split(vim.trim(raw_expression), '\n', { plain = true })
 
     local start_row, start_col, end_row, end_col = root:range()
-    local virt_text = { expression .. string.rep(' ', extra_space), state.config.highlights.latex }
+    local virt_lines = vim.tbl_map(function(expression)
+        return { { vim.trim(expression), state.config.highlights.latex } }
+    end, expressions)
     vim.api.nvim_buf_set_extmark(0, M.namespace, start_row, start_col, {
         end_row = end_row,
         end_col = end_col,
-        virt_text = { virt_text },
-        virt_text_pos = 'overlay',
+        virt_lines = virt_lines,
+        virt_lines_above = true,
     })
 end