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Canvas Threading: Difference between revisions
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→Canvas Architecture: https://forum.flightgear.org/viewtopic.php?f=71&t=28914&p=277769&hilit=#p277769
m (→Canvas Architecture: https://forum.flightgear.org/viewtopic.php?f=71&t=28914&p=277769&hilit=#p277769) |
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Realistically, all Canvas textures are however instantiated/updated using scripting space hooks that end up writing to the corresponding properties in the global property tree, this makes it much easier to manipulate a canvas/element, because you don't need to do any low-level getprop/setprop stuff, but can directly use an element specific API. | Realistically, all Canvas textures are however instantiated/updated using scripting space hooks that end up writing to the corresponding properties in the global property tree, this makes it much easier to manipulate a canvas/element, because you don't need to do any low-level getprop/setprop stuff, but can directly use an element specific API. | ||
A FlightGear Canvas is primarily a property tree in the main property tree, where attributes of the texture, and each element, are mapped to "listeners" (or updated via polling). | |||
Internally, this will dispatch events/notifications to the current texture/event. | |||
A Canvas in texture is an invisible offscreen rendering context (RTT/FBO) - it is made visible by adding a so called "placement" to the main FlightGear scenegraph, where the static texture will be replaced with one of the dynamic Canvas textures. | |||
A FlightGear Canvas supports events for UI purposes, so that listeners can be registered for events like "mouseover" etc. | |||
The Canvas scenegraph is a special thing, its root is always a Canvas group - each group can have an arbitrary number of children added, i.e. other elements (or other groups). | |||
The primary Canvas elements are 1) raster images, 2) osgText nodes, 3) map, 4) groups and 5) OpenVG paths. | |||
The FlightGear Canvas system does not understand SVG images - instead, it is using the OpenVG back-end to translate a subset of SVG/XML to Canvas properties by mapping those to OpenVG primitives. | |||
There are many features that are not supported by this SVG parser (svg.nas), but it is written in Nasal and can be easily extended to also support other features, e.g. support for raster images and/or nested SVG images. | |||
== Approach == | == Approach == | ||