<!DOCTYPE html>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/webxr_util.js"></script>
<script src="resources/webxr_test_constants.js"></script>

<script>

let testName = "Ensure framebuffer scaling works as expected.";

let fakeDeviceInitParams = TRACKED_IMMERSIVE_DEVICE;

let testFunction =
  (session, fakeDeviceController, t, sessionObjects) => new Promise((resolve, reject) => {
  let gl = sessionObjects.gl;
  let webglLayer = sessionObjects.glLayer;
  let defaultFramebufferWidth = webglLayer.framebufferWidth;
  let defaultFramebufferHeight = webglLayer.framebufferHeight;
  let nativeScale = XRWebGLLayer.getNativeFramebufferScaleFactor(session);

  t.step(() => {
    // Ensure the framebuffer default sizes and native scale are all non-zero.
    assert_greater_than(defaultFramebufferWidth, 0);
    assert_greater_than(defaultFramebufferHeight, 0);
    assert_greater_than(nativeScale, 0);

    // The native scale should be the inverse for the default framebuffer scale.
    assert_approx_equals(nativeScale, 1/fakeDeviceController.defaultFramebufferScale_, FLOAT_EPSILON);
  });

  webglLayer = new XRWebGLLayer(session, gl, { framebufferScaleFactor: nativeScale });
  t.step(() => {
    // Ensure that requesting a native scale framebuffer gives the expected result.
    assert_approx_equals(webglLayer.framebufferWidth, defaultFramebufferWidth*nativeScale, 2);
    assert_approx_equals(webglLayer.framebufferHeight, defaultFramebufferHeight*nativeScale, 2);
  });

  webglLayer = new XRWebGLLayer(session, gl, { framebufferScaleFactor: 0 });
  t.step(() => {
    // Ensure that the framebuffer has a lower bounds clamp.
    assert_greater_than(webglLayer.framebufferWidth, 0);
    assert_greater_than(webglLayer.framebufferHeight, 0);
  });

  webglLayer = new XRWebGLLayer(session, gl, { framebufferScaleFactor: 100 });
  t.step(() => {
    // Ensure that the framebuffer has a reasonable upper bounds clamp.
    assert_less_than(webglLayer.framebufferWidth, defaultFramebufferWidth*100);
    assert_less_than(webglLayer.framebufferHeight, defaultFramebufferHeight*100);
  });

  resolve();
});

xr_session_promise_test(
  testName, testFunction, fakeDeviceInitParams, 'immersive-vr');

</script>