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html5 - canvas element - Multiple layers

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Without any extension library, is it possible to have multiple layers in the same canvas element? So if I do a clearRect on the top layer, it will not erase the bottom one? Thanks. No, however, you could layer multiple <canvas> elements on top of each other and accomplish something similar. <div style="position: relative;"> <canvas id="layer1" width="100" height="100" style="position: absolute; left: 0; top: 0; z-index: 0;"></canvas> <canvas id="layer2" width="100" height="100" style="position: absolute; left: 0; top: 0; z-index: 1;"></canvas> </div> Draw your first layer on the layer1 canvas,

How to maintain multi layers of ImageViews and keep their aspect ratio based on the largest one?

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问题 Suppose I have multiple Images that I need to put one on top of the other, some might have some kind of animation appearing and some might even be draggable. the largest one which usually takes the whole screen would be the bottom in the Z-coordinate (let\'s call it the backgroundImageView ), while all of the rest appear on top of it (and on top of others). like so: backgroundImageView imageView1 , centered. imageView2 , at 60%,60% of the top left corner ... If I use a FrameLayout (which

html5 - canvas element - Multiple layers

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问题 Without any extension library, is it possible to have multiple layers in the same canvas element? So if I do a clearRect on the top layer, it will not erase the bottom one? Thanks. 回答1: No, however, you could layer multiple <canvas> elements on top of each other and accomplish something similar. <div style="position: relative;"> <canvas id="layer1" width="100" height="100" style="position: absolute; left: 0; top: 0; z-index: 0;"></canvas> <canvas id="layer2" width="100" height="100" style=

社区观点 | 关于比原链MOV巡查官制度的几点思考

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在ChainNode白皮书解密读书会01期活动中，比原链高级研究员刘秋杉带领大家领读「MOV：下一代去中心跨链 Layer 2 价值交换协议」白皮书，得到了很多粉丝的关注，其中gentledog的读书帖「关于MOV巡查官制度的几点思考」获得了读书活动的第一名。正文如下：根据白皮书，MOV中有巡查官一职防止侧链作恶。我就在想，这个制度是否存在漏洞呢？经过一番思考，似乎有以下几种攻击方式： 1、复制交易攻击巡查官发现问题并在主链上发起一笔交易，有人获取这笔交易内容后，提高手续费或者直接向网络隐瞒这笔交易，然后再发起一笔同样内容的交易，从而窃取巡查官的劳动成果。在这种情况下，巡查官能够获取的利益几乎为零，甚至为负，这样就不会有动力去巡查了。这种攻击是有对策的。有一样东西是作恶者无法复制的：钱包地址！可以采取提案（承诺）+证据的模式，巡查官可以先提交承诺（数据+钱包地址的哈希值），等区块确认后，再公布数据（钱包地址可以不用公布）。这样就能比较完美地解决这个问题了。 2、假装作恶攻击当网关节点给予的奖励大于侧链作恶者所遭受的损失时，可以采取这种攻击。侧链作恶者可以假装作恶，然后串通巡查官抢先提交作恶的证据，从网关节点处骗取奖励，当奖励大于作恶者所受到的惩罚时，作恶者就获利了。这种攻击说明，网关节点给予的奖励是有上限的，它不能大于作恶者所受到的惩罚，并不一定与作恶程度对等。 3