[1.12.2] Saving "3D" Inventory Icons to an image

Hello,

I am trying to save the icons of the games items as they appear when in your inventory (or in the crafting grid, where they appear the same as in the inventory) to an image file (PNG or GIF).

Using this thread and this thread as jumping off points to start in the right direction, and with some browsing of the OpenGL documentation and Forge documentation, I have been able to save the 2D flat icons to images (items like foods such as apple and potato and tools like pickaxes) by loading TextureMap.LOCATION_BLOCKS_TEXTURE into memory with OpenGL, writing it to a BufferedImage, and then using BufferedImage.getSubImage with the TextureAtlasSprite.getOriginX/Y  and TextureAtlasSprite.getHeight/Widthfunctions.

However, I have not been able to figure out how the save the inventory icons of items like dirt / stone / etc blocks or items like stairs / fences which appear as more "3D" than the more flat 2D inventory icons. I saw it noted in the second linked post that I may need to render the model so that I may capture a "screenshot". I have been unsuccessful in my research attempts to try and figure out how to manually render a model or how one might capture the "screenshot" of the rendered model.

It might also be worth mentioning that I am proficient in Java but quite new to Minecraft modding.

Any information you can provide or examples you could point me to to help me get started with my attempts to save the 3D inventory icons would be greatly appreciated. Thank you!