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