Fewer draw calls

Every material section of a LOD is a draw call. A far LOD with five sections costs five draw calls, even when it covers a few pixels. Fewer draw calls from LOD on the Batch LODs page gives the far LODs of static meshes fewer sections. It is off by default: tick it for the runs that should change sections.

Options

Option	Default	Meaning
Fewer draw calls from LOD	Off, LOD 2	Turns the feature on, from this LOD (1 to 7) to the last one.
Merge sections with the same material	On	Sections that draw with the same material and the same section settings (shadows, collision, ray tracing) become one. They look the same.
Drop sections under	2 %	Sections with less than this share of the triangles vanish on those LODs, from 0 to 25 %. The biggest section is never dropped. 0 keeps them.
Main material only	Off	Everything left is drawn with the material of the biggest section: one draw call. The other materials are not shown on those LODs.

The three sub-options are available while Fewer draw calls from LOD is on, and they are applied in this order. Sections are compared by the material they draw with, not by their slot: two slots with the same material can merge.

Example

SM_Kiosk_Sections has four sections with 160, 3,200, 6,400 and 21,920 triangles; slots 2 and 3 use the same material. A run with Standard and Fewer draw calls from LOD 2:

1. Merge sections with the same material joins the last two sections: three sections are left.
2. Drop sections under 2 % drops the 160-triangle section, which is 0.5 % of the 31,680 triangles: two sections are left.
3. With Main material only on, the last two would become one.

The preview shows 4 · 4 · 4 · 4 → 4 · 4 · 2 · 2 in the Draw calls column and 4 LODs from "Standard", LOD 2+: 4 → 2 draw calls in the Note.

What it changes

• Static meshes only. Skeletal meshes keep their sections.
• Generated LODs only. Hand-made (imported) LODs stay as they are.
• A changed LOD gets LOD 0’s geometry with the merged sections as its own geometry and reduces it itself, so it keeps the recipe’s triangle share. The LOD chain in the mesh details tags it merged.
• LOD Tailor notes the merged LODs in the mesh’s package, so they are not taken for hand-made LODs. This note is editor data; it is not cooked into your game.
• With Build the LOD chain on, the new LODs are merged as they are built. With it off, the mesh’s existing generated LODs from that LOD on are merged, and the preview shows the mesh as Settings.
• If merging would leave as many sections as before, the mesh’s LODs stay as they are.

Preview, export and reports

Where	What you see
Preview	Draw calls (before → after) per LOD, the changed numbers highlighted, and a note such as LOD 2+: 4 → 2 draw calls.
Export preview	Draw calls per LOD before and after in lod_plan.html, and Draw calls before and Draw calls after in lod_plan.csv.
LOD pictures	The tooltip of a picture and the captions in the HTML report give the draw calls of every LOD.
Reports	The Draw calls column in the HTML report and Draw calls per LOD in the CSV report.

Restore and reimport

• Restore last backup puts the old state back: LODs that the run merged become plain reductions again, and LODs that were merged before the run are merged again from LOD 0 the same way.
• After a reimport that changes LOD 0, LOD Tailor merges the sections of the merged LODs again from the new LOD 0, whatever Protect Imported LODs on Reimport says. The Log says “Merged the sections of LOD 2 of SM_Kiosk_Sections again from the reimported mesh.”
• A LOD you import over a merged LOD, in the mesh editor or with a reimport, is used as imported and is not merged any more.

See Reimport protection.

Tip

Small sections such as decals, trims or emissive details often carry a material of their own. Drop sections under removes them where they are only a few pixels big; raise Fewer draw calls from LOD if they disappear too early.

Command line and Python

Where	What
Commandlet	-ReduceDrawCalls -DrawCallsFromLOD=2 -DropSectionsBelow=0.02 -MainMaterialOnly with -Apply. See Command line & CI.
Python	The options reduce_draw_calls, draw_calls_from_lod, merge_same_material_sections, drop_sections_below (a fraction, 0.02 = 2 %) and merge_into_main_material; a plan entry has sections_before, sections_after and reduces_draw_calls. See Python.