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Re: [Public WebGL] Ambiguity and Non-deterministicness in the WebGL Spec
On 14/12/2010 03:57, Chris Marrin wrote:
A lazy clear operation implies a single clear to the current values
set in the state. So isn't that violating the spec. that you just
wrote: "clears the buffers to their default values"?
On 12/12/2010 04:20 PM, Gregg Tavares (wrk) wrote:
The spec has changed to effectively require a clear each time the
WebGL draw buffer is composited
WebGL presents its drawing buffer to the HTML page compositor
immediately before a compositing operation, but only if the
drawing buffer has been modified since the last compositing
operation. Before the drawing buffer is presented for compositing
the implementation shall ensure that all rendering operations have
been flushed to the drawing buffer. By default, after compositing
the contents of the drawing buffer shall be cleared to their
default values. This includes the color buffer as well as the
depth and stencil buffers if they are defined
Note that I don't say that the buffers are cleared to the current clear values in the state. This was intentional to make it clear that the state is not involved in this clear operation. But this clear operation can be done lazily. If the author first clears the buffers first (which will almost always be the case), then this clear can be skipped. Using the word "default" is really only a placeholder. We need to make it clear that it is the default value from the state, which I believe is well defined in the GLES spec.
I think that we should use the proposal you wrote in another message
in this thread:
I added the emphasized "not" as I think you inadvertently omitted
We could always say that the drawing buffers have values that are "undefined but guaranteed NOT to contain information from another process", or something like that.
So I'd rewrite as "By default (what does that mean? ed) after
compositing the contents of the drawing buffer are undefined but are
guaranteed not to contain information from another process." Then
add a non-normative note somewhere that "One way to an
implementation can guarantee buffers do not contain information from
another process is to clear the buffer to the default values
specified in OpenGL ES."
This gives maximum flexibility to the implementation while
Another point, why does this talk about buffers? Only the color
buffer is handed off for compositing so only that has the
possibility to contain information from another process. So why
mandate clearing the depth & stencil buffers after present?
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