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libghostty: add dedicated dirty row iteration + clear functions

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Add render state C APIs for iterating only rows that require a redraw
and for marking a completed frame clean in one call.  

A one-row update in a 24-row viewport reduces dirty-row discovery from 
50 calls to two, while cleanup becomes one call instead of O(N) of rows.

This lower call count is massive for environments where FFI is expensive
(Go, wasm).

The dirty next API outputs the viewport y because it jumps, unlike the
normal sequential next where its trivial for a caller to keep track.
This commit is contained in:
Mitchell Hashimoto
2026-08-15 20:56:36 -07:00
parent 746a11c721
commit 0d37f2d34d
6 changed files with 223 additions and 25 deletions
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27
example/c-vt-render/src/main.c
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@@ -165,15 +165,9 @@ int main(void) {
result = ghostty_render_state_row_cells_new(NULL, &cells);
assert(result == GHOSTTY_SUCCESS);
int row_index = 0;
while (ghostty_render_state_row_iterator_next(row_iter)) {
// Check per-row dirty state; a real renderer would skip clean rows.
bool row_dirty = false;
ghostty_render_state_row_get(
row_iter, GHOSTTY_RENDER_STATE_ROW_DATA_DIRTY, &row_dirty);
printf("Row %2d [%s]: ", row_index,
row_dirty ? "dirty" : "clean");
uint16_t row_y = 0;
while (ghostty_render_state_row_iterator_next_dirty(row_iter, &row_y)) {
printf("Row %2u [dirty]: ", row_y);
// Query the row-local selection range. Rows without a selection return
// GHOSTTY_NO_VALUE; selected rows return inclusive start/end columns.
@@ -239,22 +233,13 @@ int main(void) {
}
printf("\n");
// Clear per-row dirty flag after "rendering" it.
bool clean = false;
ghostty_render_state_row_set(
row_iter, GHOSTTY_RENDER_STATE_ROW_OPTION_DIRTY, &clean);
row_index++;
}
//! [render-row-iterate]
//! [render-dirty-reset]
// After finishing the frame, reset the global dirty state so the next
// update can report changes accurately.
GhosttyRenderStateDirty clean_state = GHOSTTY_RENDER_STATE_DIRTY_FALSE;
result = ghostty_render_state_set(
render_state, GHOSTTY_RENDER_STATE_OPTION_DIRTY, &clean_state);
// After successfully rendering the complete frame, clear both the global
// and per-row dirty state in one call.
result = ghostty_render_state_clean(render_state);
assert(result == GHOSTTY_SUCCESS);
//! [render-dirty-reset]