#!/bin/bash

# Input parameters
input_image="$1"  # Input tilemap image
output_image="$2" # Output image with transparent pixels
tile_width="$3"   # Width of each tile
tile_height="$4"  # Height of each tile

# Get the dimensions of the input image
image_width=$(identify -format "%w" "$input_image")
image_height=$(identify -format "%h" "$input_image")

# Calculate the number of tiles in both directions
tiles_across=$((image_width / tile_width))
tiles_down=$((image_height / tile_height))

# New image size (considering the 1 pixel padding between tiles)
new_width=$((tiles_across * (tile_width + 1) - 1))
new_height=$((tiles_down * (tile_height + 1) - 1))

# Create a blank canvas with a transparent background
convert -size "${new_width}x${new_height}" xc:none blank_canvas.png

# Iterate through each tile in the tilemap
for ((y = 0; y < tiles_down; y++)); do
  for ((x = 0; x < tiles_across; x++)); do
    # Extract the tile from the original image
    tile_x=$((x * tile_width))
    tile_y=$((y * tile_height))
    convert "$input_image" -crop "${tile_width}x${tile_height}+$tile_x+$tile_y" "tile_${x}_${y}.png"

    # Place the tile on the new image, accounting for the 1-pixel padding
    new_tile_x=$((x * (tile_width + 1)))
    new_tile_y=$((y * (tile_height + 1)))
    composite -geometry "+${new_tile_x}+${new_tile_y}" "tile_${x}_${y}.png" blank_canvas.png blank_canvas.png
  done
done

# Save the final image
mv blank_canvas.png "$output_image"

# Clean up temporary tiles
rm tile_*.png

echo "Output saved to $output_image"