Add Fog and a Minimap

Complete Add the Transport Truck first. The units already emit vision. This chapter adds the darkened terrain overlay and a north-up minimap.

1. Create the fog material

Create Content/Demo/Materials and a Material named M_DemoFog. Set Material Domain to Post Process and choose the Blendable Location after tonemapping.

Add these parameters with their names exactly as written:

Parameter	Type
FogTexture	Texture Sample Parameter 2D
FogWorldMin	Vector Parameter
FogWorldSize	Vector Parameter

For the material preview, assign /Engine/EngineResources/WhiteSquareTexture to FogTexture and set FogWorldSize to (1000, 1000, 0, 0). Enable Show Engine Content to find the texture. The fog render actor replaces the texture and bounds at runtime.

Build the material graph:

1. Add Absolute World Position, mask RG to get world X and Y.
2. Mask RG from FogWorldMin and FogWorldSize.
3. Subtract FogWorldMin from world XY, then divide by FogWorldSize. This is the fog UV.
4. Connect the UV to FogTexture.
5. Add SceneTexture, Scene Texture Id PostProcessInput0, and mask its RGB.
6. Add Linear Interpolate: A = scene RGB, B = FogTexture RGB, Alpha = FogTexture A.
7. Connect the result to Emissive Color.

Apply and save. Texture U follows world +X and V follows world +Y; do not flip one axis in this graph.

2. Place the fog renderer

Open LVL_DemoSkirmish. Add Sein Fog Of War Render from Place Actors. Assign M_DemoFog to Fog Post Process Material. Its post-process volume is unbound, so its transform does not determine the visible area.

Use Unexplored Opacity 1, Explored Opacity 0.75, and Smoothing Strength 1 as starting presentation values. Save and run Play Standalone.

Move the Soldier. Nearby terrain should be revealed; visited terrain should darken after leaving sight. If everything stays dark, verify the unit’s vision stamp, owning slot, and level bake. If the overlay is absent, check the renderer’s material assignment and parameter names.

3. Create the minimap widget

In Content/Demo/Blueprints/UI, create a SeinUserWidget named WBP_DemoMinimap. Use a Size Box root with Width Override and Height Override 240, containing an Overlay.

Add these full-size layers in this order:

1. Border, background a dark gray.
2. Image named TerrainImage.
3. Image named FogImage.
4. Canvas Panel named BlipCanvas.

Set TerrainImage, FogImage, and BlipCanvas to Not Hit-Testable (Self & All Children). Let the outer widget receive mouse input. Mark the three named layers Is Variable.

Add WBP_DemoMinimap to the HUD Canvas, anchored bottom-right, alignment (1, 1), offset (-24, -24), size (240, 240). Compile and save.

4. Read the map layers

In WBP_DemoMinimap, create RefreshMinimap and call it from Event Tick.

Call Get Minimap View Model. Return unless it is valid and Has Bounds is true.

• If Background Texture is valid, Set Brush From Texture on TerrainImage and show it; otherwise collapse that image so the gray Border is visible.
• If Fog Texture is valid, Set Brush From Texture on FogImage and show it; otherwise collapse FogImage.

The gray background is sufficient for the demo’s flat floor. The view model supplies fog and blips without a Scene Capture actor.

5. Draw entity markers

Create a SeinUserWidget named WBP_DemoBlip. Its root is a Border with a white brush, desired size 6 × 6, and Not Hit-Testable visibility. Add a Linear Color variable Tint, Instance Editable and Expose on Spawn. On Construct, set the Border’s Brush Color from Tint.

Extend RefreshMinimap:

1. Clear Children on BlipCanvas.
2. For each entry in the view model’s Blips, choose green for Friendly, red for Enemy, and yellow for Neutral. Use white when Selected is true.
3. Create WBP_DemoBlip with that Tint and the owning player.
4. Add Child to Canvas on BlipCanvas. Set the returned Canvas Panel Slot’s Size to (6, 6), Alignment to (0.5, 0.5), and Position to Normalized Pos * (240, 240).

The view model already filters enemy blips by visibility. Do not replace this list with an unfiltered actor search. Rebuilding these noninteractive markers each refresh is sufficient for the small demo.

6. Click to move the camera

Override On Mouse Button Down in WBP_DemoMinimap.

For Left Mouse Button, read the pointer event’s screen-space position and use Absolute to Local with the event’s Geometry. Divide by Geometry’s Local Size to obtain normalized UV. Clamp both coordinates to 0..1.

Call Minimap To World with that UV, the view model’s World Bounds Min and Max, and Ground Z. Get Owning Player Pawn and cast it to BP_DemoSkirmishCameraPawn. Call Set Camera State:

Input	Value
Pivot Location	Minimap To World result
Yaw	Get Camera Yaw
Pitch	Get Camera Pitch
Zoom Distance	Get Current Zoom Distance

Return Handled for the left click, Unhandled for other buttons. This moves only the local camera.

7. Test vision and minimap

Run Play Standalone. Check that the local Soldier and Truck appear as friendly markers, deposits appear when permitted by visibility, and moving a unit changes the revealed region. Click different parts of the minimap and confirm the camera lands at the matching world locations.

Load Soldiers into the Truck. Their separate vision should cease while contained. Unload them and check it returns. After the lobby chapter, verify enemy markers disappear outside your sight even though the other player’s units still exist.

Checkpoint

• Fog is rendered from the local observer’s vision data.
• The minimap uses the same baked world bounds and visibility-filtered entities.
• A minimap click moves the local camera without issuing a unit order.

Continue with Create the Skirmish Lobby.