How to invoke (Rust) web-sys AngleInstancedArrays?

Question

https://developer.mozilla.org/en-US/docs/Web/API/ANGLE_instanced_arrays

Given WebGL2RenderingContext as gl.

We have gl.draw_arrays_instanced.

There is also a web-sys object: web_sys::AngleInstancedArrays with functions like draw_arrays_instanced_angle.

The Web-Sys AngleInstancedArrays must be activated by listing the feature in the Cargo.toml under the dependencies.web_sys entry.

I can access the function but I can not manage to provide the first argument required, which is a reference to a web_sys::AngleInstancedArrays struct. There seems to be no way to construct such an object.

There is also the example posted here: https://developer.mozilla.org/en-US/docs/Web/API/ANGLE_instanced_arrays

I tried that approach in Rust and it doesn't work.

More unwrapping just yields a <js_sys::Object>

Then I saw that web-sys has its own web_sys::AngleInstancedArrays, and tried that. Hence the question.

From the code AngleInstancedArrays::draw_arrays_instanced_angle(&AngleInstancedArrays, GL::TRIANGLES, 0, 6, 2);, yields:

That first argument is just for illustration. The compiler is asking for an instance of AngleInstancedArrays but I can't see how to instantiate one.

Answer 1

Think what is missing is a cast. Following the javascript example ANGLE_instanced_arrays. Corresponding in web-sys get_extension, if successful, returned JsObject is of type web_sys::AngleInstancedArrays. Before using function draw_arrays_instanced_angle a cast is needed, together with the call from the question:

let etx_angle: web_sys::AngleInstancedArrays = object_js.dyn_into().unwrap();
etx_angle.draw_arrays_instanced_angle(GL::TRIANGLES, 0, 6, 2);

But as the answer above sketches, for WebGL2 the api is simpler WebGl2RenderingContext.draw_arrays_instanced

Answer 2

Based on ANGLE_instanced_arrays documentation:

• for WebGL1 you should use WebGlRenderingContext::get_extension to retrieve instance of AngleInstancedArrays.

• for WebGL2 you should be able to use WebGl2RenderingContext::draw_arrays_instanced

Note: This extension is only available to WebGL1 contexts. In WebGL2, the functionality of this extension is available on the WebGL2 context by default and the constants and methods are available without the "ANGLE" suffix.