Add common sense restrictions on viewport shape.

toji · toji · commit c6e512e30817 · 2020-03-04T16:57:28.000-08:00
diff --git a/index.bs b/index.bs
@@ -1806,7 +1806,7 @@ Depth values stored in the buffer are expected to be between <code>0.0</code> an
 
 Note: Making the scene's depth buffer available to the compositor allows some platforms to provide quality and comfort improvements such as improved reprojection.
 
-Each {{XRWebGLLayer}} MUST have a <dfn>list of viewports</dfn> which is a [=/list=] containing one [=WebGL viewport=] for each {{XRView}} the {{XRSession}} currently exposes. The viewports MUST NOT be overlapping. If [=XRWebGLLayer/composition disabled=] is <code>true</code>, the [=list of viewports=] MUST contain a single [=WebGL viewport=] that covers the [=XRWebGLLayer/context=]'s entire default framebuffer.
+Each {{XRWebGLLayer}} MUST have a <dfn>list of viewports</dfn> which is a [=/list=] containing one [=WebGL viewport=] for each {{XRView}} the {{XRSession}} currently exposes. The viewports MUST have a {{XRViewport/width}} and {{XRViewport/height}} greater than <code>0</code> and MUST describe a rectangle that does not exceed the bounds of the [=target framebuffer=]. The viewports MUST NOT be overlapping. If [=XRWebGLLayer/composition disabled=] is <code>true</code>, the [=list of viewports=] MUST contain a single [=WebGL viewport=] that covers the [=XRWebGLLayer/context=]'s entire default framebuffer.
 
 {{getViewport()}} queries the {{XRViewport}} the given {{XRView}} should use when rendering to the layer.
 
