今天來畫雲寶！
大家最喜歡哪一個彩虹小馬呢？
【兒童歌曲：https://goo.gl/MFzNd8 】
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哈囉球球 Hello ChuChu ! kids' channel　是CAPSULE.旗下，一個為幼兒與家長設立的娛樂教育頻道。

我們有兒歌童謠、教學歌曲、搖籃曲，還有關於數字、形狀、顏色的教學動畫影片，也有車車和火車的原創兒歌。
結合適合孩子的生活教育主題，如便便、刷牙、洗澡等等，來製作影片是我們的目標。
未來也會繼續創作更多安全又有趣的影片！
喜歡我們的影片請幫我們按讚+訂閱+分享

Hello ChuChu is a YouTube channel for kids and parents to watch, learn and enjoy together.
On this channel you can find nursery rhymes, educational songs and videos about learning numbers, colors, shapes and original songs about cars or trains.
We will continue to make safe and enjoyable videos for children!

試著畫了苦力怕，除了綠色的，還有紅色的，藍色的，黃色的。
然後他們動起來了！！
【兒童歌曲：https://goo.gl/MFzNd8 】
----------------------------------------------------------------------------------------------------
哈囉球球 Hello ChuChu ! kids' channel　是CAPSULE.旗下，一個為幼兒與家長設立的娛樂教育頻道。

我們有兒歌童謠、教學歌曲、搖籃曲，還有關於數字、形狀、顏色的教學動畫影片，也有車車和火車的原創兒歌。
結合適合孩子的生活教育主題，如便便、刷牙、洗澡等等，來製作影片是我們的目標。
未來也會繼續創作更多安全又有趣的影片！
喜歡我們的影片請幫我們按讚+訂閱+分享

Hello ChuChu is a YouTube channel for kids and parents to watch, learn and enjoy together.
On this channel you can find nursery rhymes, educational songs and videos about learning numbers, colors, shapes and original songs about cars or trains.
We will continue to make safe and enjoyable videos for children!

📜 [專欄新文章] Gas Efficient Card Drawing in Solidity

✍️ Ping Chen

📥 歡迎投稿： https://medium.com/taipei-ethereum-meetup #徵技術分享文 #使用心得 #教學文 #medium

Assign random numbers as the index of newly minted NFTs

Scenario

The fun of generative art NFT projects depends on randomness. The industry standard is “blind box”, where both the images’ serial number and the NFTs’ index are predetermined but will be shifted randomly when the selling period ends. (They call it “reveal”) This approach effectively solves the randomness issue. However, it also requires buyers to wait until the campaign terminates. What if buyers want to know the exact card right away? We’ll need a reliable onchain card drawing solution.

The creator of Astrogator🐊 isn’t a fan of blind boxes; instead, it thinks unpacking cards right after purchase is more interesting.

Spec

When initializing this NFT contract, the creator will determine the total supply of it. And there will be an iterable function that is randomly picking a number from the remaining pool. The number must be in range and must not collide with any existing ones.

Our top priority is accessibility/gas efficiency. Given that gas cost on Ethereum is damn high nowadays, we need an elegant algorithm to control gas expanse at an acceptable range.

Achieving robust randomness isn’t the primary goal here. We assume there’s no strong financial incentive to cheat, so the RNG isn’t specified. Implementers can bring their own source of randomness that they think is good enough.

Implementation

Overview

The implementation is pretty short and straightforward. Imagine there’s an array that contains all remaining(unsold) cards. When drawIndex() is called, it generates a (uniform) random seed to draw a card from the array, shortens the array, and returns the selected card.

Algorithm

Drawing X cards from a deck with the same X amount of cards is equal to shuffling the deck and dealing them sequentially. It’s not a surprise that our algorithm is similar to random shuffling, and the only difference is turning that classic algo into an interactive version.

A typical random shuffle looks like this: for an array with N elements, you randomly pick a number i in (0,N), swap array[0] and array[i], then choose another number i in (1,N), swap array[1] and array[i], and so on. Eventually, you’ll get a mathematically random array in O(N) time.

So, the concept of our random card dealing is the same. When a user mints a new card, the smart contract picks a number in the array as NFT index, then grabs a number from the tail to fill the vacancy, in order to keep the array continuous.

Tweak

Furthermore, as long as the space of the NFT index is known, we don’t need to declare/initialize an array(which is super gas-intensive). Instead, assume there’s such an array that the n-th element is n, we don’t actually initialize it (so it is an array only contains “0”) until the rule is broken.

For the convenience of explanation, let’s call that mapping cache. If cache[i] is empty, it should be interpreted as i instead of 0. On the other hand, when a number is chosen and used, we’ll need to fill it up with another unused number. An intuitive method is to pick a number from the end of the array, since the length of the array is going to decrease by 1.

By doing so, the gas cost in the worst-case scenario is bound to be constant.

Performance and limitation

Comparing with the normal ascending index NFT minting, our random NFT implementation requires two extra SSTORE and one extra SLOAD, which cost 12600 ~ 27600 (5000+20000+2600) excess gas per token minted.

Theoretically, any instantly generated onchain random number is vulnerable. We can restrict contract interaction to mitigate risk. The mitigation is far from perfect, but it is the tradeoff that we have to accept.

ping.eth

Gas Efficient Card Drawing in Solidity was originally published in Taipei Ethereum Meetup on Medium, where people are continuing the conversation by highlighting and responding to this story.

👏 歡迎轉載分享鼓掌

這個影片是給7歲以下孩子學習的數學影片，增強孩子基礎數學學習，從小了解數學的架構。

歡迎大家加入會員，贊助此影音頻道

藍色框 - 英文教學相關影片
粉色框 - 英文文法與口語教學相關影片
黃色框 - 數學教學和唐詩相關影片
綠色框 - 英文單詞相關影片
橘色框 - 英文聽力相關影片

Hello! I'm finally back with another tutorial!💗 Sorry that I've been too busy that I haven't posted in a while. I've been trying to gather good footage and testing out with this new app Prequel to see the best color pastel recipe for videos & instagram reels to share with you guys! The app is free and has so so many amazing filters and effects, I'm so in love with this app! This tutorial video is a bit fast because I edited it for Reels, so i did put the adjustment numbers on the side, so feel free to pause the video when watching

終於有剪輯好了新的教學影片了！🙏最近真的很忙到沒有很多時間剪輯發片，希望你們會喜歡這個教學。我最近一直測試新下載的Prequel App，然後最終測試出最好看的調色Recipe分享給大家收藏起來！最近很喜歡這種彩色很夏天的韓系粉彩風格的色調，希望你們也會喜歡！影片的速度是比較快的，所以需要的話可以暫停影片然後follow旁邊我有寫的數字跟著調色❤️

What App I Use:
- Prequel App
Download: https://www.prequel.app

What Fonts I Use:
- Next Southerland Serif
Download: https://www.dafont.com/next-southerland-serif.font
- Galano Grotesque
Download: https://www.dafontfree.io/galano-grotesque-font/


Connect with Me!
♡ Instagram | @x.yunny.x
♡ Instagram | @my.eatz
♡ Email | yunnyhou@gmail.com

Songs
Music by Lukey - Honeydream - https://thmatc.co/?l=178253EC

What I use:
♡ Camera | Canon G7X Mark ii
♡ Doodles | SketchBook iPad App
♡ Editing | Final Cut Pro x Adobe Premiere Pro

這個影片是給7歲以下孩子學習的數學影片，增強孩子基礎數學學習。

歡迎大家加入會員，贊助此影音頻道

藍色框 - 英文教學相關影片
粉色框 - 英文文法與口語教學相關影片
黃色框 - 數學教學和唐詩相關影片
綠色框 - 英文單詞相關影片
橘色框 - 英文聽力相關影片