Just click on the palette at the bottom left and click where you want to place each color. Click the question mark to change palettes (press once changes to Object palette, a second time changes it back). Click the dollar sign to get hex output. Right now it is only compatible with RGBDS, but it also gives raw hex numbers if needed. Press space to hide the hex data again (make sure no text is selected, click out of the box at the top of the screen). Click on the <> symbol to vary the height and width of your map. Clicking on the dollar sign will then give you the individual tiles in rows, starting with the top left and working to the bottom right (like reading a book). This allows for easy tilemapping because this is the same way a program like RGBDS would read it when it assembles your code. I highly recommend fulscreen, it will make it easier to see what you are drawing. P.S. : You can also "click" by pressing the f key. It is very helpful when you are stuck with a track pad.
Still the early version, but It does what is intended. Credit to the gbdev community, all of the information needed for this project can be found there: https://gbdev.io/ A nice tool for viewing tiles can be found here: https://www.huderlem.com/demos/gameboy2bpp.html And should you want to use it for real, you can go here: https://gbdev.io/rgbds-live/ Or here: https://rgbds.gbdev.io/ RGBDS also has their own graphics converter if you would prefer that. I also heavily recommend the following guide: https://eldred.fr/gb-asm-tutorial/ which is really good, but it's also unfinished, so you might have to do your own research for a few things.(Or you can try asking me also, but I don't know all of the answers. I can help you with sprites though!) Also, technically you don't have to make use of the option to change palettes. It won't change the actual tile data in any way, it's just for visuals. The default is 11100100 (or $E4) Things I hope to add: removing repeat tiles tile mapping?