keep text from overflowing right margin

I've been sloppy about this so far, and outside of tests I can't find
any examples where it matters, but it matters in a potential fork where
I'm rendering multiple columns of text.

It's unfortunate that my tests have this level of brittleness. What I'd
really like to assert in many of these changed lines is that the text
stays inside the margins and that more text would overflow margins.

1 files changed, 15 insertions, 5 deletions

diff --git a/text.lua b/text.lua
index e28a9dc..fdf2418 100644
--- a/text.lua
+++ b/text.lua
@@ -807,21 +807,23 @@ function Text.nearest_cursor_pos(line, x, left)
   assert(false)
 end
 
-function Text.nearest_pos_less_than(line, x)  -- x DOES NOT include left margin
+-- return the nearest index of line (in utf8 code points) which lies entirely
+-- within x pixels of the left margin
+function Text.nearest_pos_less_than(line, x)
+--?   print('-- nearest_pos_less_than', line, x)
   if x == 0 then
     return 1
   end
   local len = utf8.len(line)
-  local max_x = Text.x(line, len+1)
+  local max_x = Text.x_after(line, len)
   if x > max_x then
     return len+1
   end
   local left, right = 1, len+1
---?   print('--')
   while true do
     local curr = math.floor((left+right)/2)
-    local currxmin = Text.x(line, curr+1)
-    local currxmax = Text.x(line, curr+2)
+    local currxmin = Text.x_after(line, curr+1)
+    local currxmax = Text.x_after(line, curr+2)
 --?     print(x, left, right, curr, currxmin, currxmax)
     if currxmin <= x and x < currxmax then
       return curr
@@ -838,6 +840,14 @@ function Text.nearest_pos_less_than(line, x)  -- x DOES NOT include left margin
   assert(false)
 end
 
+function Text.x_after(s, pos)
+  local offset = Text.offset(s, math.min(pos+1, #s+1))
+  local s_before = s:sub(1, offset-1)
+--?   print('^'..s_before..'$')
+  local text_before = App.newText(love.graphics.getFont(), s_before)
+  return App.width(text_before)
+end
+
 function Text.x(s, pos)
   local offset = Text.offset(s, pos)
   local s_before = s:sub(1, offset-1)