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https://github.com/OrcaSlicer/OrcaSlicer.git
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Hanif Koh
8b2ae48e4a
On a shallow surface the band of a layer that the layer above leaves exposed is narrower than a grid cell, so whether the layer is the topmost occupant of any cell flickers from layer to layer and the band's segments, inner walls and solid infill hidden by role, came and went in a dashed ring. That band is always in the same place: the strip just outside the outer wall of the layer above, or of the layer below for the underside of an overhang. The classifier now keeps the outer-wall cell map of the previous and next layers as well as the current one, rotating like the footprints, and keeps any segment whose midpoint lies within a line and a half, or a cell if larger, of a neighbouring layer's outer wall. It can only add segments, so no hole is opened by it; what it over-keeps is the covered strip under the neighbour's wall.
120 lines
7.4 KiB
Markdown
120 lines
7.4 KiB
Markdown
# G-code preview while dragging
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The sliced preview draws every toolpath segment of the plate as an instanced box. On a large
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plate that is tens of millions of segments, and the frame is GPU-bound: the cost is the number of
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instances drawn, not anything the CPU does per frame. Dragging the camera over such a plate cannot
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keep up. The `preview_reduced_detail_mode` preference (*Graphics > G-code Preview*, off by
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default) lets the preview draw less while the user drags and put the full toolpaths back when they
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let go.
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| Preference | Values | Effect |
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|---|---|---|
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| `preview_reduced_detail_mode` | `off`, `solid`, `layers`, `outer_walls`, `shell` | what is drawn while dragging |
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| `preview_reduced_detail_layer_stride` | 1–20 | one layer in every N is kept by the toolpath modes |
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libvgcode (`src/libvgcode`) builds and binds the reduced toolpath set, `GCodeViewer` maps the
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preferences onto it and draws the solid model, and `GLCanvas3D` decides when the user is dragging.
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The OpenGL ES path keeps a single set and ignores the preference.
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## Two sets, one walk
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`ViewerImpl::update_enabled_entities()` walks the visible vertex range once and fills two segment
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index buffers side by side: the **full** set and the **reduced** set (segments and options).
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Building them together is what makes switching free: starting or ending a drag is a buffer
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binding, never a rebuild. A change of mode or stride does rebuild. Nothing is built while the mode
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is off, and the reduced buffers are then uploaded empty so that the last set does not stay
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allocated.
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Whatever the mode leaves out, the bottom and top layers of the visible range are kept whole: they
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are the faces the range cuts open, and the top is what the user is looking at.
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### Modes
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- `EndLayersOnly` (`solid` in the preference) keeps only the two end layers. `GCodeViewer` then
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draws the sliced objects and the prime tower as opaque solids, see below.
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- `LayersOnly` (`layers`) keeps every role of one layer in every stride.
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- `OuterWallsOnly` (`outer_walls`) keeps the outer and overhang perimeters of one layer in every
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stride. The prime tower and supports have other roles and are left out.
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- `ShellOnly` (`shell`) keeps what the shell extraction below marks as visible surface, of one
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layer in every stride, plus whatever a view from above or below sees of the skipped layers, so
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that a step does not vanish. It is the only mode that knows the prime tower's outside from its
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inside.
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## The solid model
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The preview already loads the sliced objects as shells for its translucent ghost.
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`GCodeViewer::render_solid_model()` draws those shells opaque, in their filament colors, with the
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`gouraud` shader, whose z range cuts them to the visible layer range. The two toolpath layers of
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the reduced set are drawn afterwards and cap the cut with what was really printed there. The
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shells hold only the objects, so while this mode is on the prime tower is added from its sliced
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mesh, positioned as the print placed it. It is added or removed on its own when the mode changes,
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without reloading the objects, keeps its opaque color so that it never appears among the
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translucent shells, and stays out of their bounding box. Supports have no mesh and are not shown,
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and `load_shells()` drops every non-model-part volume, so a negative volume is not cut out.
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A plate whose shells are not loaded keeps drawing toolpaths, since the solid model would leave
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only the end layers.
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## Shell extraction
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`ViewerImpl::update_shell_bitset()` classifies every extrusion segment once per load, on demand
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the first time the shell mode needs it, and records the result in four bit sets. It is purely
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geometric so that the wipe tower, whose every segment shares one role, works as well as the
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objects.
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Each layer is rasterized into a coarse 2D **occupancy grid** over the print's footprint: cells
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are 0.5 mm, or coarser so that the grid is at most 1024 cells across. The footprint is then
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**closed** with a radius of 2.5 mm so that sparse infill and support read as the solid area they
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belong to, while holes wider than 5 mm stay open. The closing dilates each 8-connected component
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separately and leaves a cell that two components both reach empty, so the gap between two objects
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standing close together is never bridged and both of their facing walls stay on the shell;
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fragments under eight cells do not spread and are absorbed by whatever reaches them. A separable
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erosion shrinks the result back, and the raw cells are OR-ed in again so that a closing never
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loses one.
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A cell is a **shell cell** when it is filled and any of its six neighbours, four in the layer,
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one below, one above, is not. A segment is on the shell when at least half of the cells it
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crosses are shell cells: walls run along the shell, infill only touches it at the ends. The
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interior infill roles and gap fill are excluded regardless, since short infill segments hugging a
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wall would otherwise pass by the thousand.
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Two refinements keep sloped surfaces closed:
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- **Near-wall segments.** The step between one layer's outer wall and the next is often
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narrower than a cell. An inner wall (`Perimeter`) segment whose midpoint lies within a line and
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a half of an outer or overhang perimeter of the same layer is kept as well. So is any segment,
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whatever its role, whose midpoint lies within that reach, or a cell if larger, of an outer wall
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of the layer above or below: that strip is the exposed band of the step, which the cell tests
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cannot see when it is narrower than a cell.
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- **Top and bottom visibility.** The same pass records the highest and lowest layer occupying
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each cell over the whole print. A segment whose layer is the topmost occupant of any cell it
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crosses is visible from above, and likewise from below with the lowest. These segments are kept
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even when their layer is skipped by the stride.
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The layer range is split across up to eight `std::async` workers, each owning its grids. An
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allocation failure on a huge print falls back to marking every segment as shell, which leaves out
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only the hidden infill roles.
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## Deciding that the user is dragging
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`GLCanvas3D::_update_preview_interaction()` runs at the top of every preview frame, before the
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canvas decides whether to reuse its cached scene, so that the switch lands in that frame. Dragging
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is `GLCanvas3D::is_user_interacting()`, the same answer the scene cache reads: the camera, the
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navigator, a gizmo, the rectangle selection or either slider being held. A slider reports this from
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ImGui's active id rather than its dirty flag, which is raised and consumed inside one frame. A
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wheel step has no duration, so it holds the reduced set for a 150 ms settle time instead, and the
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frame that restores the toolpaths is scheduled for when that time runs out, since the render timer
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only wakes the idle loop. A drag cut short by focus or capture loss is ended explicitly, and a
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button release wakes the idle loop, because on some platforms nothing else would until the next
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input.
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## Reused scene frames
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`GLCanvas3D` keeps its last scene pass for frames that only rebuild the overlay (`SceneCache`). Its
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key covers the canvas size, the camera and hover state, not what the toolpath sets draw, so a frame
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that reuses the scene must never be one on which the set is switched.
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`_update_preview_interaction()` therefore reports whether the bound set changed, and a frame on
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which it did redraws the scene. The canvas neither captures nor reuses the scene while the user
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drags, so no reduced frame outlives a drag, and the frame that ends a wheel's settle time is
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requested as a full frame.
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