xtk renderer3D's pick() produce errors in webgl2 enabled browsers - xtk

Question

Has anyone used xtk with webgl2 to do the pick() call? specifically
renderer3d's.
Error: WebGL: drawArrays: Feedback loop detected...renderer3D.js:1977:7
Error: WebGL: readPixels: Out-of-bounds reads with readPixels are deprecated, and may be slow. renderer3D.js:1445:5

Answer 1

For the first error, feedback loops have always been invalid and an error in WebGL. From the WebGL 1 spec section 6.26
6.26 Feedback Loops Between Textures and the Framebuffer
In the OpenGL ES 2.0 API, it's possible to make calls that both write to and read from the same texture, creating a feedback loop. It specifies that where these feedback loops exist, undefined behavior results.
In the WebGL API, such operations that would cause such feedback loops (by the definitions in the OpenGL ES 2.0 spec) will instead generate an INVALID_OPERATION error.
As for the 2nd error that's not a valid WebGL error. Which version of which browser is generating that error?
Here's the WebGL conformance test to make sure you can read out of bounds
https://www.khronos.org/registry/webgl/sdk/tests/conformance/reading/read-pixels-test.html?webglVersion=1&quiet=0
And here's a snippet showing reading out of bounds does not generate an error.
['webgl', 'webgl2'].forEach(check);
function check(version) {
log(`checking ${version}`);
const gl = document.createElement("canvas").getContext(version);
if (!gl) {
log(`${version} not supported`);
return;
}
const pixel = new Uint8Array(4);
// read off the left bottom
gl.readPixels(-10, -10, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixel);
// read off the right top
gl.readPixels(400, 300, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixel);
//
const error = gl.getError();
log(error ? `error was ${error} reading out of bounds`
: "there were no errors reading out of bounds");
}
function log(...args) {
const elem = document.createElement("pre");
elem.textContent = [...args].join();
document.body.appendChild(elem);
}
Maybe file bugs with xtk?