Minimap Topographic Map

Generates and renders topographic contour lines from terrain heightmap data.

Overview

ui_apps_minimap_topomap scans the terrain heightmap, generates contour lines via marching squares, and builds a spatial index for efficient rendering on the minimap background.

Extension path: lua/ge/extensions/ui/apps/minimap/topomap.lua

Exports (M)

Internals

Loading Pipeline

loadTopoMap() executes three steps:

1. Calculate bounds - Uses navgraph node positions to determine terrain area (capped at ±2000m)
2. Scan heightmap - Samples core_terrain.getTerrainHeight() on a 5m grid
3. Generate contours - Runs marching squares at 2.5m intervals, builds kd-tree index

Marching Squares

Classic cell-based contour extraction. For each grid cell, the four corner heights are compared against each contour level to determine edge intersections:

-- Cell corners classified as above/below contour level
local caseIndex = 0
if d00 >= zc then caseIndex = caseIndex + 1 end
if d10 >= zc then caseIndex = caseIndex + 2 end
if d11 >= zc then caseIndex = caseIndex + 4 end
if d01 >= zc then caseIndex = caseIndex + 8 end
-- Cases 0 and 15 = no intersection

Each intersection produces a line segment stored as {level, x1, y1, x2, y2}.

Rendering

drawContours queries the kd-tree for segments near the camera, transforms to minimap coords, and draws with brightness proportional to elevation:

local clr = color(128 + level*1.25, 128 + level*1.25, 128 + level*1.25, 255)
local thickness = 1 + (level%10 == 0 and 0.5 or 0)  -- major contours thicker

Rendering is capped at 5000 segments per frame for performance.

Reset

Topo data is cleared on onClientEndMission and onClientStartMission, requiring re-generation per level.

How It Works

1. Minimap calls loadTopoMap() to generate contour data from terrain
2. Marching squares produces thousands of line segments at 2.5m elevation intervals
3. Segments are indexed in a kd-tree for spatial queries
4. Each frame, drawContours renders nearby segments with elevation-based brightness
5. Major contour lines (every 10m) are rendered slightly thicker

Additional Exports

The following exports are available but not yet documented in detail:

• M.drawContours
• M.getContourQuadtree
• M.getContourSegments
• M.getHeightmapBounds
• M.getHeightmapData
• M.isLoaded
• M.loadTopoMap
• M.onClientEndMission
• M.onClientStartMission