KHR_parallel_shader_compile extension

const ext = gl.getExtension("KHR_parallel_shader_compile");

// Assuming lists of `shaders` and `programs`:
for (const x of shaders) gl.compileShader(x); // Never check compile status unless subsequent linking fails.
for (const x of programs) gl.linkProgram(x);

// Generator yielding a progress ratio [0.0, 1.0].
// Without the extension, this will jank and only check one program per generation.
function* linkingProgress(programs) {
  const ext = gl.getExtension("KHR_parallel_shader_compile");
  let todo = programs.slice();
  while (todo.length) {
    if (ext) {
      todo = todo.filter(
        (x) => !gl.getProgramParameter(x, ext.COMPLETION_STATUS_KHR),
      );
    } else {
      const x = todo.pop();
      gl.getProgramParameter(x, gl.LINK_STATUS);
    }
    if (!todo.length) return;
    yield 1.0 - todo.length / programs.length;
  }
}