Sloped belts and filters drawn as one belt turned to 45° (t40)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/PROJECT_MAP.md

@@ -356,11 +356,12 @@ Drawing (src/render/): browser only. This file: the renderer state R, colour tab
 Propagated coloured light from glowing and burning cells.
 - functions: builtForLight, looseForLight, computeLight
 
-### src/render/slope-belts.js (28 lines)
-A slope's band uses world coordinates, so its stripes never restart at block joints.
-- functions: slopeBeltAt, slopeBeltColor
+### src/render/slope-belts.js (127 lines)
+Drawing only: the face stays on its simulation cells; the band hangs below it.
+- functions: slopeBeltConnections, flatBeltCaps, prepareSlopeBelts, slopeBeltSegment, slopeBeltCorner, slopeBeltShape, slopeBeltAt, slopeBeltColor
+- variables: slopeBeltJoins, slopeBeltHalo, beltCaps, slopeAcross, slopeAlong, slopeDistance
 
-### src/render/world.js (422 lines)
+### src/render/world.js (440 lines)
 Scale colour without changing the smooth-look class.
 - functions: fogColor, diagonalTubeJoins, diagonalTubeShape, diagonalTubeBlock, drawWorld
 - variables: TUBE_CLASS, diagonalJoins, diagonalAcross, diagonalAlong, diagonalCap
@@ -378,7 +379,11 @@ Smooth look: WebGL setup, texture uploads, drawing and adaptive resolution.
 - functions: smCompile, smoothAvailable, smUpload, smoothDraw, smoothPace
 - variables: SM, smBytes
 
-### src/render/smooth-shaders.js (393 lines)
+### src/render/slope-belt-shader.js (84 lines)
+Smooth slope shading, kept beside the shared CPU geometry in slope-belts.js.
+- variables: SM_SLOPE_HELPERS, SM_SLOPE_DRAW
+
+### src/render/smooth-shaders.js (369 lines)
 Smooth shaders: vertex and fragment programs for the rounded world look.
 - variables: SM_VS, SM_FS
 
@@ -471,7 +476,7 @@ Gamepad input.
 - functions: padPressed, pollPad
 - variables: PAD
 
-### src/ui/previews.js (227 lines)
+### src/ui/previews.js (237 lines)
 Cursor previews: shared grid helpers, air streaks and tool preview dispatch.
 - functions: blockRectPx, drawGrid, previewColor, drawAirStreaks, drawReachCircle, drawPreviews, previewBlock
 
@@ -522,6 +527,7 @@ The frame loop and boot.
 - `test/t_pipes.js`: Pipes, pumps and outlets move liquids; the Grinder grinds waste rock for trace ore.
 - `test/t_racks.js`: Rack intake, FIFO storage, gate, removal and saved-state validation.
 - `test/t_sim_optimizations.js`: Optimized paths must match the full roof scan and the original heat loop exactly.
+- `test/t_slope_belt_art.js`: Drawing geometry against real parts, without changing transport.
 - `test/t_slope_belts.js`: Sloped belts: transport, joins, sorting, persistence and the actual drag controls.
 - `test/t_slopes.js`: Sloped walls: flow, sealed joints, building, refunds and persistence.
 - `test/t_smooth.py`: The smooth look: the WebGL pass compiles, draws, falls back cleanly, and the thermal lens still works.