Because information about CEMU in 21:9 started to grow from everywhere without a real guide, I decided to write it step by step. I post it here and will be a copy of my other post on Reddit. I started earlier, but because BotW was not supported, I didn't. Now it is, so here is how to do it 
Feel free to share your codes for other games.
CEMU 1.8.0
Credits: Ethrillo, Nfanja, Esppiral, Flocker, Cirez
Let's start with The Legend of Zelda : The Wind Waker HD
* 1 Launch CEMU and select "Options > Fullscreen scaling > Stretch"
* 2 Launch your game (in our exemple, Wind Walker HD) and select "Tools > Memory searcher"
* 3 In the top box, search for 1.77777777 (float is selected) and double click on the one with address "0x1004aaf0" to add it in the bottom list (this address will change regarding of your game, check at the bottom of this post) (http://i.imgur.com/wkm07D0.png)
* 4 In the bottom list, click "freeze" the item you just added, then click on the value to edit it, and change the value with 2.37 (2560x1080) or 2.38 (3440x1440).
* 5 Download a 1440 pack of your game: https://github.com/slashiee/cemu_graphic_packs/tree/master/Quality and open the rules.txt with a text editor. Change all 2560 by 3440. (This step is to get a native 3440x1440 3D when fullscreen will be activated, otherwise the 2560 will be stretched, and the game less sharp)
* 6 Your 3D is now "deformed".
* 7 Just switch in fullscreen mode, and here is the result
(Crédits : getdls)
Notes:
+As you can see, all 2D elements cannot be (for now) converted. Only the 3D is 21:9 adapted.
+When you don't have the address, just scan during the game, edit all the 1.77777777 value with 2.37 or 2.38 until you find the one who correct the ratio. Note that some games need to load a new game to apply the change.
+Leaving CEMU will reset this setting.
Captain Toad: Treasure Tracker
Donkey Kong Country: Tropical Freeze
Mario Kart 8
Paper Mario Color Splash
Super Mario 3D World
Super Smash Bros.
The Legend of Zelda : The Wind Waker HD
The Legend of Zelda : Breath of the Wild
Xenoblade Chronicles X
Yoshi's Woolly World
========== VALUES =========
1.77777777 (16:9)
2.37 (21:9 2560x1080)
2.38 (21:9 3440x1440)
**Please share addresses you found for other games
Feel free to share your codes for other games.
CEMU 1.8.0
Credits: Ethrillo, Nfanja, Esppiral, Flocker, Cirez
Let's start with The Legend of Zelda : The Wind Waker HD
* 1 Launch CEMU and select "Options > Fullscreen scaling > Stretch"
* 2 Launch your game (in our exemple, Wind Walker HD) and select "Tools > Memory searcher"
* 3 In the top box, search for 1.77777777 (float is selected) and double click on the one with address "0x1004aaf0" to add it in the bottom list (this address will change regarding of your game, check at the bottom of this post) (http://i.imgur.com/wkm07D0.png)
* 4 In the bottom list, click "freeze" the item you just added, then click on the value to edit it, and change the value with 2.37 (2560x1080) or 2.38 (3440x1440).
* 5 Download a 1440 pack of your game: https://github.com/slashiee/cemu_graphic_packs/tree/master/Quality and open the rules.txt with a text editor. Change all 2560 by 3440. (This step is to get a native 3440x1440 3D when fullscreen will be activated, otherwise the 2560 will be stretched, and the game less sharp)
* 6 Your 3D is now "deformed".
* 7 Just switch in fullscreen mode, and here is the result
(Crédits : getdls)
Notes:
+As you can see, all 2D elements cannot be (for now) converted. Only the 3D is 21:9 adapted.
+When you don't have the address, just scan during the game, edit all the 1.77777777 value with 2.37 or 2.38 until you find the one who correct the ratio. Note that some games need to load a new game to apply the change.
+Leaving CEMU will reset this setting.
Captain Toad: Treasure Tracker
Third address starting with 0x3 (thanks slashiee)
Donkey Kong Country: Tropical Freeze
0x108cb6a8 AND 0x108d1b28 AND 0x4abb2344
Mario Kart 8
First address starting with 0x3
Paper Mario Color Splash
0x10039be4
Super Mario 3D World
Third address starting with 0x3 (thanks slashiee)
Super Smash Bros.
0x132314c4 (thanks jediyoshi)
The Legend of Zelda : The Wind Waker HD
0x1004aaf0
The Legend of Zelda : Breath of the Wild
========================== Zelda : Breath of the Wild Guide ======================
Many thanks to Ethrillo and Nfanja for the solution!
* 1 Launch CEMU, BotW, and go ingame (3D must be loaded)
* 2 Download Cheat Engine 6.6 or above http://cheatengine.org/download.php, install it, launch it.
* 3 On Cheat Engine, select the blinking Computer icon on the left, and in the process list, select Cemu and "open"
* 4 On the right settings, in "value type" select "Array of byte" and in the Hex line, fill with:
and clic "First scan".
* 5 You'll see a result line on the left, double clic on it to add it in the bottom panel
* 6 In the bottom panel, double clic on the value to change it. Replace with:
* 7 Now clic on new scan, and with the same options, search for:
* 8 You'll have 1 or 2 results. Select the first one and same as before, change the value with:
For (21:9 2560x1080):
For (21:9 3440x1440):
* 9 The game is now 21:9, just switch in full screen
*10 A fix for HUD as been posted by getdls on the slahiee GIT: https://github.com/slashiee/cemu_graphic_packs/issues/56#issuecomment-304745081
Many thanks to Ethrillo and Nfanja for the solution!
* 1 Launch CEMU, BotW, and go ingame (3D must be loaded)
* 2 Download Cheat Engine 6.6 or above http://cheatengine.org/download.php, install it, launch it.
* 3 On Cheat Engine, select the blinking Computer icon on the left, and in the process list, select Cemu and "open"
* 4 On the right settings, in "value type" select "Array of byte" and in the Hex line, fill with:
and clic "First scan".
* 5 You'll see a result line on the left, double clic on it to add it in the bottom panel
* 6 In the bottom panel, double clic on the value to change it. Replace with:
* 7 Now clic on new scan, and with the same options, search for:
* 8 You'll have 1 or 2 results. Select the first one and same as before, change the value with:
For (21:9 2560x1080):
For (21:9 3440x1440):
* 9 The game is now 21:9, just switch in full screen
*10 A fix for HUD as been posted by getdls on the slahiee GIT: https://github.com/slashiee/cemu_graphic_packs/issues/56#issuecomment-304745081
Xenoblade Chronicles X
Yoshi's Woolly World
========== VALUES =========
1.77777777 (16:9)
2.37 (21:9 2560x1080)
2.38 (21:9 3440x1440)
**Please share addresses you found for other games
Last edited by artik1024,
