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https://github.com/OrcaSlicer/OrcaSlicer.git
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Hanif Koh
493896260e
The solid model is one answer to a preview that cannot keep up with a drag; a reviewer asked for the two that keep the drag view made of toolpaths. The checkbox is now a combobox, "Simplify preview while dragging", with Off, Solid model, Skip layers and Outer walls, and a spin, "Draw one layer in every N", for the toolpath modes. Off is the default, and with it nothing is built. Skip layers keeps one layer in every N. Outer walls keeps the outer and overhang perimeters of those layers, so the prime tower and supports, whose segments have other roles, drop out of it. Both keep the bottom and top layers of the visible range whole, as the solid model does, so the faces the range cuts open stay what was printed there. libvgcode takes the choice as EReducedDetailMode and a stride; the sets are rebuilt when either changes, and drawing from the reduced one is still a buffer binding. A mode change reaches the loaded preview at once, as the checkbox did.
76 lines
4.6 KiB
Markdown
76 lines
4.6 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` | 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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## 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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## 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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