imgmath: Fix relative file path (#10965)

CHANGES

@@ -16,6 +16,8 @@ Features added
 Bugs fixed
 ----------
 
+* #10944: imgmath:  Fix resolving image paths for files in nested folders.
+
 Testing
 --------
 

sphinx/ext/imgmath.py

@@ -207,10 +207,9 @@ def render_math(
     """Render the LaTeX math expression *math* using latex and dvipng or
     dvisvgm.
 
-    Return the filename relative to the built document and the "depth",
+    Return the image absolute filename and the "depth",
     that is, the distance of image bottom and baseline in pixels, if the
     option to use preview_latex is switched on.
-    Also return the temporary and destination files.
 
     Error handling may seem strange, but follows a pattern: if LaTeX or dvipng
     (dvisvgm) aren't available, only a warning is generated (since that enables
@@ -317,7 +316,8 @@ def html_visit_math(self: HTMLTranslator, node: nodes.math) -> None:
             image_format = self.builder.config.imgmath_image_format.lower()
             img_src = render_maths_to_base64(image_format, rendered_path)
         else:
-            relative_path = path.relpath(rendered_path, self.builder.outdir)
+            bname = path.basename(rendered_path)
+            relative_path = path.join(self.builder.imgpath, 'math', bname)
             img_src = relative_path.replace(path.sep, '/')
         c = f'<img class="math" src="{img_src}"' + get_tooltip(self, node)
         if depth is not None:
@@ -357,7 +357,8 @@ def html_visit_displaymath(self: HTMLTranslator, node: nodes.math_block) -> None
             image_format = self.builder.config.imgmath_image_format.lower()
             img_src = render_maths_to_base64(image_format, rendered_path)
         else:
-            relative_path = path.relpath(rendered_path, self.builder.outdir)
+            bname = path.basename(rendered_path)
+            relative_path = path.join(self.builder.imgpath, 'math', bname)
             img_src = relative_path.replace(path.sep, '/')
         self.body.append(f'<img src="{img_src}"' + get_tooltip(self, node) +
                          '/></p>\n</div>')