anil.recoil.org
Kitty Graphics Protocol in OCaml
terminal
graphics
ocaml
kgpcat
+5
bin/dune
+5
bin/dune
+352
bin/kgpcat.ml
+352
bin/kgpcat.ml
···
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(*---------------------------------------------------------------------------
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Copyright (c) 2025 Anil Madhavapeddy. All rights reserved.
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SPDX-License-Identifier: ISC
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---------------------------------------------------------------------------*)
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(* kgpcat - Display images in the terminal using Kitty Graphics Protocol *)
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open Cmdliner
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module K = Kgp
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type align = Center | Left | Right
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type fit = Width | Height | Both | None_
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type config = {
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files : string list;
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clear : bool;
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clear_all : bool;
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detect_support : bool;
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align : align; [@warning "-69"]
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place : (int * int * int * int) option;
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scale_up : bool; [@warning "-69"]
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fit : fit; [@warning "-69"]
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z_index : int;
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unicode_placeholder : bool;
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no_trailing_newline : bool;
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hold : bool;
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graphics_mode : K.Terminal.graphics_mode;
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}
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(* Default image size in cells when not using --place *)
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let default_rows = 10
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let default_cols = 20
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(* Read file contents *)
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let read_file filename =
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let ic = open_in_bin filename in
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let n = in_channel_length ic in
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let s = really_input_string ic n in
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close_in ic;
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s
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(* Read from stdin *)
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let read_stdin () =
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let buf = Buffer.create 4096 in
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try
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while true do
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Buffer.add_channel buf stdin 4096
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done;
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assert false
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with End_of_file -> Buffer.contents buf
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(* Detect if stdin has data *)
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let stdin_has_data () =
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let fd = Unix.descr_of_in_channel stdin in
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not (Unix.isatty fd)
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(* Send command to terminal *)
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let send ?(tmux = false) cmd ~data =
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let s = if tmux then K.to_string_tmux cmd ~data else K.to_string cmd ~data in
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print_string s;
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flush stdout
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(* Check if file is a supported format (PNG only) *)
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let is_supported_format filename =
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let ext =
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try
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let dot = String.rindex filename '.' in
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String.lowercase_ascii (String.sub filename (dot + 1) (String.length filename - dot - 1))
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with Not_found -> ""
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in
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ext = "png" || filename = "stdin"
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(* Display a single image *)
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let display_image config filename data =
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let resolved_mode = K.Terminal.resolve_mode config.graphics_mode in
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match resolved_mode with
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| `Placeholder ->
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(* No graphics support - show placeholder text *)
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Printf.printf "[Image: %s (%d bytes)]\n" filename (String.length data)
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| `Graphics | `Tmux ->
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let use_tmux = resolved_mode = `Tmux in
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(* Use unicode placeholders if requested or if in tmux mode *)
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let use_unicode = config.unicode_placeholder || use_tmux in
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let cols, rows =
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match config.place with
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| Some (w, h, _, _) -> (w, h)
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| None -> (default_cols, default_rows)
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in
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if use_unicode then (
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(* Unicode placeholder mode: transmit image, then output placeholder chars *)
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let image_id = K.next_image_id () in
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let placement =
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match config.place with
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| Some (w, h, x, y) ->
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K.Placement.make ~columns:w ~rows:h ~cell_x_offset:x ~cell_y_offset:y
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~z_index:config.z_index ~unicode_placeholder:true ~cursor:`Static ()
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| None ->
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let z = if config.z_index <> 0 then Some config.z_index else None in
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K.Placement.make ~columns:cols ~rows ?z_index:z ~unicode_placeholder:true
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~cursor:`Static ()
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in
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(* Transmit the image data with virtual placement *)
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let cmd =
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K.transmit_and_display ~image_id ~format:`Png ~placement ~quiet:`Errors_only ()
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in
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send ~tmux:use_tmux cmd ~data;
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(* Output unicode placeholder characters that reference the image *)
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let buf = Buffer.create 256 in
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K.Unicode_placeholder.write buf ~image_id ~rows ~cols ();
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print_string (Buffer.contents buf);
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if not config.no_trailing_newline then print_newline ()
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) else (
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(* Direct graphics mode *)
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let image_id = K.next_image_id () in
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let placement =
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match config.place with
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| Some (w, h, x, y) ->
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Some
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(K.Placement.make ~columns:w ~rows:h ~cell_x_offset:x ~cell_y_offset:y
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~z_index:config.z_index ~cursor:`Static ())
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| None ->
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let z = if config.z_index <> 0 then Some config.z_index else None in
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Some
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(K.Placement.make ?z_index:z
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~cursor:(if config.no_trailing_newline then `Static else `Move) ())
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in
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let cmd =
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K.transmit_and_display ~image_id ~format:`Png ?placement ~quiet:`Errors_only ()
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in
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send ~tmux:use_tmux cmd ~data;
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if not config.no_trailing_newline && config.place = None then print_newline ()
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)
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(* Clear all images *)
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let do_clear () =
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send (K.delete `All_visible) ~data:""
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(* Clear all images including scrollback *)
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let do_clear_all () =
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(* Delete all images by ID range 1 to max, freeing data *)
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send (K.delete ~free:true (`By_id_range (1, 4294967295))) ~data:""
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(* Detect terminal support *)
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let do_detect_support () =
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if K.Terminal.is_graphics_terminal () then (
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let mode =
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if K.Terminal.is_tmux () then "tmux"
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else if K.Terminal.is_kitty () then "kitty"
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else if K.Terminal.is_wezterm () then "wezterm"
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else if K.Terminal.is_ghostty () then "ghostty"
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else "stream"
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in
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Printf.eprintf "%s\n" mode;
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0
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) else (
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Printf.eprintf "not supported\n";
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1
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)
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(* Main run function *)
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let run config =
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(* Handle clear operations first *)
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if config.clear_all then do_clear_all ()
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else if config.clear then do_clear ();
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(* Handle detect support *)
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if config.detect_support then exit (do_detect_support ());
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(* Process files *)
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let files =
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if config.files = [] && stdin_has_data () then [ "-" ] else config.files
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in
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if files = [] && not config.clear && not config.clear_all then (
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Printf.eprintf "Usage: kgpcat [OPTIONS] IMAGE_FILE...\n";
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Printf.eprintf "Try 'kgpcat --help' for more information.\n";
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exit 1);
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List.iter
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(fun file ->
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let name = if file = "-" then "stdin" else file in
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if not (is_supported_format name) then
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Printf.eprintf "Error: %s is not a PNG file (only PNG format is supported)\n" file
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else
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try
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let data =
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if file = "-" then read_stdin () else read_file file
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in
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display_image config name data
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with
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| Sys_error msg ->
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Printf.eprintf "Error reading %s: %s\n" file msg
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| exn ->
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Printf.eprintf "Error processing %s: %s\n" file (Printexc.to_string exn))
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files;
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(* Ensure all output is flushed before exiting *)
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flush stdout;
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if config.hold then (
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Printf.eprintf "Press Enter to exit...";
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flush stderr;
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ignore (read_line ()))
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(* Cmdliner argument definitions *)
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let files_arg =
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Arg.(value & pos_all file [] & info [] ~docv:"IMAGE" ~doc:"Image files to display.")
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let clear_arg =
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let doc = "Remove all images currently displayed on the screen." in
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Arg.(value & flag & info [ "clear" ] ~doc)
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let clear_all_arg =
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let doc = "Remove all images from screen and scrollback." in
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Arg.(value & flag & info [ "clear-all" ] ~doc)
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let detect_support_arg =
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let doc =
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"Detect support for image display in the terminal. Exits with code 0 if \
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supported, 1 otherwise. Prints the supported transfer mode to stderr."
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in
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Arg.(value & flag & info [ "detect-support" ] ~doc)
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let align_arg =
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let doc = "Horizontal alignment for the displayed image." in
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let align_enum = Arg.enum [ ("center", Center); ("left", Left); ("right", Right) ] in
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Arg.(value & opt align_enum Center & info [ "align" ] ~doc ~docv:"ALIGN")
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let place_arg =
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let doc =
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"Display image in specified rectangle. Format: WxH@X,Y where W and H are \
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width and height in cells, and X,Y is the position. Example: 40x20@10,5"
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in
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let parse s =
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try
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let at_pos = String.index s '@' in
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let size_part = String.sub s 0 at_pos in
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let pos_part = String.sub s (at_pos + 1) (String.length s - at_pos - 1) in
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let x_pos = String.index size_part 'x' in
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let w = int_of_string (String.sub size_part 0 x_pos) in
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let h = int_of_string (String.sub size_part (x_pos + 1) (String.length size_part - x_pos - 1)) in
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let comma_pos = String.index pos_part ',' in
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let x = int_of_string (String.sub pos_part 0 comma_pos) in
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let y = int_of_string (String.sub pos_part (comma_pos + 1) (String.length pos_part - comma_pos - 1)) in
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Ok (w, h, x, y)
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with _ -> Error (`Msg "Invalid place format. Use WxH@X,Y (e.g., 40x20@10,5)")
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in
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let print ppf (w, h, x, y) = Format.fprintf ppf "%dx%d@%d,%d" w h x y in
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let place_conv = Arg.conv (parse, print) in
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Arg.(value & opt (some place_conv) None & info [ "place" ] ~doc ~docv:"WxH@X,Y")
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let scale_up_arg =
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let doc =
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"Scale up images smaller than the specified area to use as much of the \
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area as possible."
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in
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Arg.(value & flag & info [ "scale-up" ] ~doc)
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let fit_arg =
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let doc = "Control how the image is scaled relative to the screen." in
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let fit_enum =
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Arg.enum [ ("width", Width); ("height", Height); ("both", Both); ("none", None_) ]
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in
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Arg.(value & opt fit_enum Width & info [ "fit" ] ~doc ~docv:"FIT")
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let z_index_arg =
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let doc =
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"Z-index of the image. Negative values display text on top of the image."
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in
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Arg.(value & opt int 0 & info [ "z"; "z-index" ] ~doc ~docv:"Z")
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let unicode_placeholder_arg =
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let doc =
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"Use Unicode placeholder method to display images. This allows images to \
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scroll properly with text in terminals and multiplexers. Automatically \
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enabled when using tmux passthrough mode."
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in
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Arg.(value & flag & info [ "unicode-placeholder" ] ~doc)
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let no_trailing_newline_arg =
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let doc = "Don't move cursor to next line after displaying an image." in
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Arg.(value & flag & info [ "n"; "no-trailing-newline" ] ~doc)
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let hold_arg =
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let doc = "Wait for a key press before exiting after displaying images." in
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Arg.(value & flag & info [ "hold" ] ~doc)
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let config_term =
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let combine files clear clear_all detect_support align place scale_up fit z_index
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unicode_placeholder no_trailing_newline hold graphics_mode =
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{
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files;
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clear;
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clear_all;
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detect_support;
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align;
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place;
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scale_up;
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fit;
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z_index;
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unicode_placeholder;
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no_trailing_newline;
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hold;
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graphics_mode;
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}
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in
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Term.(
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const combine
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$ files_arg
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$ clear_arg
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$ clear_all_arg
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$ detect_support_arg
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$ align_arg
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$ place_arg
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$ scale_up_arg
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$ fit_arg
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$ z_index_arg
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$ unicode_placeholder_arg
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$ no_trailing_newline_arg
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$ hold_arg
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$ Kgp_cli.graphics_term)
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let cmd =
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let doc = "Display images in the terminal using Kitty Graphics Protocol" in
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let man =
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[
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`S Manpage.s_description;
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`P
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"$(tname) displays images in terminals that support the Kitty Graphics \
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Protocol (Kitty, WezTerm, Konsole, Ghostty, etc.).";
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`P
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"You can specify multiple image files. If no files are given and stdin \
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is not a terminal, image data is read from stdin.";
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`S Manpage.s_examples;
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`P "Display an image:";
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`Pre " $(tname) photo.png";
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`P "Display multiple images:";
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`Pre " $(tname) *.png";
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`P "Display image from stdin:";
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`Pre " curl -s https://example.com/image.png | $(tname)";
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`P "Display image at specific position:";
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`Pre " $(tname) --place 40x20@10,5 photo.png";
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`P "Clear all displayed images:";
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`Pre " $(tname) --clear";
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`S Kgp_cli.graphics_docs;
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]
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in
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let info = Cmd.info "kgpcat" ~version:"%%VERSION%%" ~doc ~man in
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Cmd.v info Term.(const run $ config_term)
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let () = exit (Cmd.eval cmd)