W3C home > Mailing lists > Public > whatwg@whatwg.org > July 2012

Re: [whatwg] Why does CanvasRenderingContext2D.drawImage not draw a video's poster?

From: Mark Callow <callow_mark@hicorp.co.jp>
Date: Wed, 18 Jul 2012 13:04:16 +0900
Message-ID: <500635C0.5030007@hicorp.co.jp>
To: whatwg@lists.whatwg.org
On 18/07/2012 00:17, Silvia Pfeiffer wrote:
> I think this is simply an idea that hasn't been raised before. I like
> it. Though even then sometimes there may be nothing when there is no
> explicit poster and preload is set to none.
The language gives me the impression that drawing nothing was a
deliberate choice, in particular because later on it says:

    When the |drawImage()
    <http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-context-2d-drawimage>|
    method is passed an animated image as its image argument, the user
    agent must use the poster frame of the animation, or, if there is no
    poster frame, the first frame of the animation.

Speaking of which, how does one specify the "poster frame" for an
animated image? There is no poster attribute on an img element. Is this
something specified in the file format? A quick search didn't reveal any
such for animated GIF or APNG files.

Drawing a video's poster, when available, seems much more user-friendly
to me.

Regards

    -Mark


> On Tue, Jul 17, 2012 at 9:58 AM, Mark Callow <callow_mark@hicorp.co.jp> wrote:
>> The spec. for CanvasRenderingContext2D.drawImage says draw nothing when
>> a video element's readyState is  HAVE_NOTHING or HAVE_METADATA. I was
>> wondering why this was chosen vs. drawing the poster. A search in the
>> list archive didn't turn up any discussion or explanation.
>>
>> Regards
>>
>>     -Mark
>>

-- 
注意:この電子メールには、株式会社エイチアイの機密情報が含まれている場合
が有ります。正式なメール受信者では無い場合はメール複製、 再配信または情
報の使用を固く禁じております。エラー、手違いでこのメールを受け取られまし
たら削除を行い配信者にご連絡をお願いいたし ます。

NOTE: This electronic mail message may contain confidential and
privileged information from HI Corporation. If you are not the intended
recipient, any disclosure, photocopying, distribution or use of the
contents of the received information is prohibited. If you have received
this e-mail in error, please notify the sender immediately and
permanently delete this message and all related copies.
Received on Wednesday, 18 July 2012 04:04:48 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Wednesday, 30 January 2013 18:48:09 GMT