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Add a generation counter to the kitty graphics image storage. Every
content mutation (image transmit/replace, placement add, delete)
assigns the storage a fresh stamp, and every image is stamped when
it is added or replaced.
This solves two problems:
First, a retransmission of the same image ID with identical dimensions
was previously undetectable by anything comparing width, height, format,
and data length; the per-image stamp changes on every add/replace, so caches
keyed on it always see the change. Second, the dirty flag was the only
storage-wide signal, and it is also set by scrolling and resizing, which move
placements without changing contents. The generation is only bumped by content
mutations, so an unchanged value means the placement set and all
image data are identical and consumers can skip re-reading them,
recomputing only placement geometry.
The generation replaces Image.transmit_time entirely: newest-image
lookup by number, eviction ordering, and the renderer's texture
staleness checks all key on it now. A monotonic counter strictly
orders transmissions where Instant-based times could collide within
clock resolution (the renderer previously assumed equal timestamps
meant identical images), and this removes a syscall and an error
path per transmission.
Delete commands now only mark a mutation (dirty flag and
generation) when they actually remove something. A delete-all runs
on every screen clear, so previously every ESC [ 2 J dirtied the
image state even with no images stored. Eviction via setLimit also
now marks the state dirty, which it previously did not.
Both generations are exposed through libghostty-vt as
GHOSTTY_KITTY_GRAPHICS_DATA_GENERATION and
GHOSTTY_KITTY_IMAGE_DATA_GENERATION (uint64_t), and the headers now
document that stored image data is always post-inflate/post-decode:
COMPRESSION always reports NONE, FORMAT is never PNG, and DATA_PTR
is raw pixels ready for GPU upload.
uint64_t gen = 0;
ghostty_kitty_graphics_get(
graphics, GHOSTTY_KITTY_GRAPHICS_DATA_GENERATION, &gen);
if (gen == last_gen) return; // nothing changed, skip re-reads
Examples
Standalone projects demonstrating the Ghostty library APIs.
The directories starting with c- use the C API and the directories
starting with zig- use the Zig API.
Every example can be built and run using zig build and zig build run
from within the respective example directory.
Even the C API examples use the Zig build system (not the language) to
build the project.
Running an Example
cd example/<dir>
zig build run