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Donner SVG 0.8.0-pre
SVG editor and embeddable C++20 engine.
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Donner SVG 0.8.0-pre
SVG editor and embeddable C++20 engine.
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The single source of truth for the editor's zoom-step model. More...
#include <algorithm>#include <cmath>Namespaces | |
| namespace | donner |
| Top-level Donner namespace, which is split into different sub-namespaces such as donner::svg and donner::css. | |
Functions | |
| double | donner::editor::PinchWheelDeltaPerLnScale () |
| Wheel deltaY, in CSS pixels, that a browser trackpad pinch carries per unit of ln(scale). | |
| double | donner::editor::PinchScrollUnitGain () |
| Gain applied to a discriminated browser trackpad-pinch scroll unit so the classifier's pow(kWheelZoomStep, units) becomes exp(rawUnits): with the engines' deltaY = -100 * ln(scale) synthesis (100 px per scroll unit), desktop parity requires multiplying units by 1 / ln(kWheelZoomStep). | |
| double | donner::editor::MaxPinchScrollUnitsPerEvent () |
| Per-event clamp for discriminated pinch units, in post-gain scroll units: caps one event's zoom factor at 1.5x (or 1/1.5) so a misclassified event is merely brisk rather than catastrophic. Real trackpad pinch events carry per-event magnifications well under this bound. | |
| double | donner::editor::ApplyPinchScrollUnitGain (double rawScrollUnits) |
| Apply the one and only pinch gain to a raw scroll-unit delta. | |
Variables | |
| constexpr double | donner::editor::kWheelZoomStep = 1.1 |
| Multiplicative zoom step applied per +1.0 wheel/scroll unit. | |
| constexpr double | donner::editor::kWasmWheelPixelsPerScrollUnit = 100.0 |
| Wheel pixels that the Wasm GLFW port treats as one scroll unit. | |
The single source of truth for the editor's zoom-step model.
Three independent producers feed the same render-pane classifier: the mouse wheel, the native macOS pinch monitor, and the browser trackpad pinch bridge. Each one has to be calibrated against the same step constant, so the numbers live here and nowhere else. Duplicating them has already produced one silent 2x drift between the desktop and browser pinch paths.
Browser pinch has exactly one gain authority. Producers - Chromium and Gecko natively, WebKit through the bootstrap's gesturechange bridge - all emit UNGAINED wheel deltas of -kWasmWheelPixelsPerScrollUnit * ln(scale), and ApplyPinchScrollUnitGain in the input bridge's pinch discriminator is the only place that gain is applied. Gaining at both ends is a silent 1 / ln(kWheelZoomStep) speedup, which is what made Safari pinch-zoom unusable; every engine now flows through identical policy code.
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inlinenodiscard |
Apply the one and only pinch gain to a raw scroll-unit delta.
This is the single consumption-side gain authority for every browser pinch path. EditorInputBridge calls it once per discriminated pinch event and nothing else in the editor may multiply pinch units again; producers hand over ungained units and this function turns them into the scroll units the classifier's pow(kWheelZoomStep, units) expects.
| rawScrollUnits | Ungained scroll units, i.e. -deltaY / 100 straight out of the Wasm GLFW port. |
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inlinenodiscard |
Gain applied to a discriminated browser trackpad-pinch scroll unit so the classifier's pow(kWheelZoomStep, units) becomes exp(rawUnits): with the engines' deltaY = -100 * ln(scale) synthesis (100 px per scroll unit), desktop parity requires multiplying units by 1 / ln(kWheelZoomStep).
The two cases ARE separable: a synthesized pinch carries the DOM ctrlKey flag while no Ctrl/Cmd key is physically held, which the input bridge observes by comparing the capture-phase DOM flag against glfwGetKey. Discriminated pinch events get this gain so a browser pinch matches the desktop's zoom = 1 + magnification per gesture event; a real ctrl+mouse-wheel keeps gain 1.0 and the discrete kWheelZoomStep per notch.
Prefer ApplyPinchScrollUnitGain, which also applies the safety clamp.
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inlinenodiscard |
Wheel deltaY, in CSS pixels, that a browser trackpad pinch carries per unit of ln(scale).
This is a wire-shape constant, not a gain. Chromium and Gecko already deliver a trackpad pinch as a ctrl-flagged wheel event on the same channel as a real ctrl+mouse-wheel zoom, using exactly this shape: Chromium synthesizes deltaY = -100 * ln(1 + magnification) (components/input/touchpad_pinch_event_queue.cc) and Gecko synthesizes deltaY = -100 * magnification (widget/InputData.cpp), equal to first order for real per-event magnifications. Only WebKit withholds that channel and reports the non-standard gesturestart/gesturechange events instead, so donner/editor/wasm/editor-bootstrap.js bridges those into the identical ungained shape. The editor publishes this value to the page so the bridge cannot drift from it.
ONE GAIN AUTHORITY. Every producer emits ungained units and the single consumer-side gain, ApplyPinchScrollUnitGain, converts them once. The Safari bridge used to pre-multiply by 1 / ln(kWheelZoomStep) at synthesis while the discriminator multiplied by it again at consumption, which zoomed Safari about 10.5x too fast in log space until the per-event clamp pinned every gesture to a full 1.5x step. Do not reintroduce a producer-side gain: calibrate producers to this shape and leave the gain where it is.
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inlineconstexpr |
Wheel pixels that the Wasm GLFW port treats as one scroll unit.
emscripten-glfw converts a DOM_DELTA_PIXEL wheel event into yoffset = -deltaY / 100 (the same convention SDL uses). The divisor is fixed by the port, so anything synthesizing wheel pixels for the editor has to pre-multiply by it to land on the scroll units the classifier expects.
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inlineconstexpr |
Multiplicative zoom step applied per +1.0 wheel/scroll unit.
ClassifyRenderPaneScrollGesture interprets a zoom gesture as pow(kWheelZoomStep, scrollDelta.y), and PinchMagnificationToScrollDelta inverts that mapping. Every producer of scroll deltas is calibrated against this one value.
1.15.0