Coherent UI provides support for customization of IO handling using the url protocol coui. Any resource that is loaded via the coui protocol is going to be loaded via the Coherent::UI::FileHandler interface provided to CreateViewContext.

If a view is loaded via the coui protocol and all its resources are referenced with relative URLs then all the resources are loaded via coui too.

The default implementation of Coherent::UI::FileHandler takes the name of the resource and uses it as path relative to the current working directory. For example coui://ui/hud.html?first_run=1 will be resolved to <current_working_directory>/ui/hud.html

For a sample using custom IO see Sample 01 - Custom File Handler Tutorial

Coui URL Parsing

coui links are parsed as standard URLs and they are expected to be of the appropriate format. This means that coui links can have host, port, path, etc. components. The host component is mandatory and the URL parsed forbids paths outside the host directory.

This can lead to unexpected behavior is the coui link is formatted incorrectly. Let's take for example the following directory structure:

Resources
+--Html
|  |--index.html
|
+--Images
   |--image.jpg

If index.html refers to image.jpg using <img src="../Images/image.jpg" /> and the coui link used is coui://Html/index.html, the image will not be loaded. This is because the host is assumed to be Html and the referenced resource is outside the host.

We recommend placing all your UI resources in a single folder acting as a host (or if that's not possible, using an artificial host such as coui://MyArtificialHost/Html/index.html) to avoid such cases. The example could be fixed using a link such as coui://Resources/Html/index.html. The referenced resource would thus become coui://Resources/Images/image.jpg because it would still be in the host directory, Resources. When using the default handler for filesystem assets, placing the UI resources in a single folder is the way to go (Resources in this example). In the case where Resources is an artificial host, the URL should be parsed to suit your needs in the file handler's ReadFile and WriteFile methods to obtain the correct asset path.

Asynchronous IO

Coherent::UI::FileHandler, Coherent::UI::ResourceResponce and Coherent::UI::ResponseData allow to easily to implement asynchronous loading of resources. The only special moment is that

MUST be called on the thread that is doing Coherent::UI::ViewContext::Update