Clipping planes (section view)

OCCT provides Graphic3d_ClipPlane — clipping at the OpenGL level, without modifying geometry. Existing difference() for sectioning is a modelling operation; clipping planes are purely visual.

Key API (via OCC.Core)

Class/Method	Role
Graphic3d_ClipPlane(gp_Pln)	Clipping plane from a geometric plane
plane.SetOn() / SetOff()	Toggle
plane.SetCapping(True)	Fill the cut surface with a color
plane.SetCappingColor(Quantity_Color)	Capping fill color
V3d_View.AddClipPlane(plane)	Apply to entire viewport
V3d_View.RemoveClipPlane(plane)	Remove from viewport
PrsMgr_PresentableObject.AddClipPlane(plane)	Apply to a single AIS object
V3d_View.SetClipPlanes()	Replace all planes at once

Two approaches

Approach	Scope	Capping	Complexity
Per-view (V3d_View.AddClipPlane)	All AIS objects	Single color for all	Low
Per-object (AIS_ColoredShape.AddClipPlane)	Per AIS object	Different per object	High

Storage

• BcadState gets clipping plane state: clip_plane_on: bool, clip_plane_axis: int (0=X, 1=Y, 2=Z), clip_plane_pos: float, clip_plane_capping: bool
• GUI stores in settings.conf under [general] (like fn_polygon_threshold)

IPC protocol (rqq.py)

Request	Parameters	Action
RQ_SET_CLIP_PLANE	axis, position, on	Create/reposition plane
RQ_REMOVE_CLIP_PLANES	—	Remove all planes
RQ_SET_CAPPING	on, color	Toggle/set capping

GUI (main_window.py)

ImGui panel (or toolbar section):

• Checkbox "Show section"
• Axis selector (X/Y/Z) — radio buttons
• Slider for position (0.0–1.0 of bounding box diagonal)
• Checkbox "Capping"
• Color picker for capping color

Implementation steps (worker side)

1. Viewer3d.set_clip_plane(axis: int, pos: float, on: bool) in boccviewer.py:
   • Remove existing clip planes from V3d_View
   • If on: create gp_Pln from axis + pos, wrap in Graphic3d_ClipPlane, call View.AddClipPlane(plane)
2. Viewer3d.remove_clip_planes() — iterate and remove all
3. Viewer3d.set_capping(on: bool, color: tuple) — set on active plane
4. Handle in worker_engine.py — new branch for RQ_SET_CLIP_PLANE etc.
5. Update image → send RP_ACK

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Texture mapping

Textures are an extension of per-face appearance, logically part of color(). The same propagation machinery that handles _face_colors handles textures — they are just another attribute of a face's material.

Storage

# scl_shape.py — single dict, value is (color, texture_path) pair
_face_material: dict[int, tuple[Quantity_ColorRGBA | None, str | None]]
# (None, None)   → default material
# (color, None)  → solid color (current behaviour)
# (None, path)   → pure texture, no tint
# (color, path)  → modulated texture (color × texture)

Propagation

All existing propagation functions treat _face_material as opaque. The dict value is carried through without inspection:

Function	Mechanism	Change
_map_colors(builder, sources)	Generated(), Modified(), IsSame()	Also carries _face_material values
_map_unified_colors(unifier, ...)	ShapeUpgrade_UnifySameDomain history	Same
_adjacency_fill_colors(...)	Edge-adjacency fill for _offset_3d	Same
transform_shape()	Re-hash faces through TShap	Updates both tuple elements
transform_gtrsh()	Same for grouped transforms	Same
extrude/revolve/loft/offset	Source face → all result faces	Carries (color, path) pair

Display

_display_main_face_colors in scl_shape.py expands:

color	texture	Action
None	None	Default (no custom attributes)
color	None	SetCustomColor(face, color) — existing path
None	path	AIS_ColoredDrawer → ShadingAspect → Aspect → SetTextureMap(map) + SetTextureMapOn(), modulate off
color	path	Both SetCustomColor() and SetTextureMap(), modulate on

OCCT mechanism per face: ```python from OCC.Core.Graphic3d import Graphic3d_Texture2D, Graphic3d_AspectFillArea3d from OCC.Core.AIS import AIS_ColoredDrawer

drawer = AIS_ColoredDrawer() shading = drawer.ShadingAspect() aspect = shading.Aspect() # Graphic3d_AspectFillArea3d aspect.SetTextureMap(Graphic3d_Texture2D(path)) aspect.SetTextureMapOn()

if color is also set:

ais_shp.SetCustomColor(face, color)

aspect.EnableTextureModulate() -- default is on

aspects_map.Bind(face, drawer) ```

Language syntax

// Solid color (existing)
color("red") cube(10);

// Pure texture (no tint)
color(texture="wood.png") cube(10);

// Modulated texture (tinted by color)
color("red", texture="checker.png") cube(10);

// Color + alpha + texture
color(c="red", alpha=0.5, texture="marble.png") sphere(5);

• texture parameter: path to PNG/JPG (file resolution like surface())
• If file not found → warning, fallback to color or default
• OpenSCAD ignores texture= → warning about unknown parameter + color shown

Face material propagation through booleans

union() {
  color("red", texture="wood.png") cube(10);
  color("blue") cube(5);
}

_fuse_parts → _map_colors maps source faces to result faces. Each source face's (color, texture) is looked up by hash and assigned via Generated()/Modified()/IsSame() to the corresponding result face.

If a result face is new (no history) → (None, None) → default.