User Images

Overview

User images is a feature of Prysm that allows developers to use textures loaded on the GPU for their UI. User images also allows specifying the content rectangle where the actual image is. This can be used if the image has padding or is part of a texture atlas.

This lets you achieve the following use cases:

  • Improve the loading time of pages by preparing the textures in advance instead loading them on request.
  • Reduce memory footprint when the engine and the UI share textures, by having the texture stored in GPU memory only once, instead of twice (once for the engine and once for Prysm).
  • Use custom image formats.
  • Make use of Unity’s texture compressing to save space and memory.

How To Use User Images For Preloading Textures

  • All images that are going to be used as preloaded must be located at the root level of
Assets/Resources/Cohtml/SharedImages/

  • The Prysm resource handler will search this path first when an image is requested. Unity will ensure that any textures found in that folder are loaded and they will be shared for use with Prysm.

  • Proper URL format:

    • coui://preloaded/ prefix
    • without image extension.
    • at the root of the folder Assets/Resources/Cohtml/SharedImages/.

Preloaded Images HTML Example 

<!DOCTYPE html>
<head>
</head>
<body>
    <img src="coui://preloaded/my_image_name">
</body>
</html>

Lifetime of user image resources

Reference flow when using user image resources as background-image:

  1. Create an element with a style which has user image resource for a background-image.
  2. When the element’s style is evaluated, the style will add a reference to the resource.
  3. The reference will be removed when:
    • The background-image in the element’s style is changed.
    • The style of the element is removed or the whole element is removed from the DOM tree.

Lifetime flow in <img>:

  1. Create <img> element with a user image resource specified by the src attribute.
  2. The element will add a reference to the resource.
  3. The reference will be removed when:
    • The src attribute is changed.
    • The Garbage Collector destroys the element.