Backends: Amend, docs + extra comments. (#3330, #3245)

imgui_draw.cpp

@@ -717,8 +717,11 @@ void ImDrawList::AddPolyline(const ImVec2* points, const int points_count, ImU32
             // [PATH 1] Texture-based lines (thick or non-thick)
             // [PATH 2] Non texture-based lines (non-thick)
 
-            // The width of the geometry we need to draw - this is essentially <thickness> pixels for the line itself, plus one pixel for AA
-            // We don't use AA_SIZE here because the +1 is tied to the generated texture and so alternate values won't work without changes to that code
+            // The width of the geometry we need to draw - this is essentially <thickness> pixels for the line itself, plus "one pixel" for AA.
+            // - In the texture-based path, we don't use AA_SIZE here because the +1 is tied to the generated texture
+            //   (see ImFontAtlasBuildRenderLinesTexData() function), and so alternate values won't work without changes to that code.
+            // - In the non texture-based paths, we would allow AA_SIZE to potentially be != 1.0f with a patch (e.g. fringe_scale patch to
+            //   allow scaling geometry while preserving one-screen-pixel AA fringe).
             const float half_draw_size = use_texture ? ((thickness * 0.5f) + 1) : AA_SIZE;
 
             // If line is not closed, the first and last points need to be generated differently as there are no normals to blend