Decimating Models

Once you have a model, carry out the following steps to decimate your model:

Part 1

1. First using Photoshop or gimp, reduce your file size. 
2. Go into textures - reduce the size of the images one by one (don't go too small)
3. After you scale down, override for each image 
4. Use GLtf to GLB Packer https://glb-packer.glitch.me/ - which compresses all the things into one file 

Part 2

In Blender: 

1. Open your GLB in Blender (delete the default cube first)
2. Click through the model hierarchy on the right till you see a green mesh icon, select the "parent" (one above the green), go to object mode & select all, CTRL J (while mouse in the 3d View) to join all the bits
3. Below green icon push CTRL B to select the rest of the hierarchy and click delete hierarchy 
4. Then Go to Edit mode > Mesh > Merge by distance - the larger the distance the smaller you are making the model but watch out for distortion 
5. Zoom in on detailed areas and merge there to simplify further 
6. Export as GLB 

(Blender is a free 3D computer graphics software)

Reduce texture size
- This is the most important for file size and avoiding app crashes.

1. First using Photoshop or gimp, reduce your file size. 
2. Go into textures - reduce the size of the images one by one (don't go too small)
3. After you scale down, override for each image.
4. If you can use Blender, save textures .jpg instead of png, tiff or tga to reduce the size and replace textures.
5. Use GLtf to GLB Packer https://glb-packer.glitch.me/ - which compresses all the things into one file 

Reduce object count
- This is the most important for performance.

1. Import your model in Blender.
2. Press F3 and type ‘select linked material’ and click. (Keyboard shortcut is Shift+L)
3. Objects that have the same material are selected.
4. Press F3 and type ‘join’ and click. (Keyboard shortcut is Control+J)
5. Repeat 2~4 until the objects are merged by material.

Reduce vertex count
- This is important to reduce file size and improve performance.

1. Select an object that you want to reduce vertex count.
2. Merge vertices. (This could cause smoothen edges)
   2-1. Go to ‘Edit Mode’ by pressing the ‘tab’ key. (Or clicking ‘Object Mode’ box on the left-top)
   2-2. Press ‘1’ to vertex mode and ‘A’ to select all vertices.
   2-3. Press F3 and type ‘merge by distance’ and click. (Keyboard shortcut is M and select ‘By Distance’)
   2-3. Press ‘tab’ again to go back to the ‘Object Mode’.
3. Reduce vertex count using Decimate Modifier.
   3-1. Go to ‘Modifier Property’ on the right menu.
   3-2. Click ‘Add Modifier’ and select ‘Decimate’.
   3-3. Change ‘Ratio’ number like 0.5.
   3-4. Hover your mouse cursor on the modifier and press ‘Ctrl+A’ to apply it.
4. Repeat 1~3 until you reduce vertices of all objects.