foot/render.h
Daniel Eklöf 299186a654
render: when double-buffering, pre-apply previous frame's damage early
Foot likes it when compositor releases buffer immediately, as that
means we only have to re-render the cells that have changed since the
last frame.

For various reasons, not all compositors do this. In this case, foot
is typically forced to switch between two buffers, i.e. double-buffer.

In this case, each frame starts with copying over the damage from the
previous frame, to the new frame. Then we start rendering the updated
cells.

Bringing over the previous frame's damage can be slow, if the changed
area was large (e.g. when scrolling one or a few lines, or on full
screen updates). It's also done single-threaded. Thus it not only
slows down frame rendering, but pauses everything else (i.e. input
processing). All in all, it reduces performance and increases input
latency.

But we don't have to wait until it's time to render a frame to copy
over the previous frame's damage. We can do that as soon as the
compositor has released the buffer (for the frame _before_ the
previous frame). And we can do this in a thread.

This frees up foot to continue processing input, and reduces frame
rendering time since we can now start rendering the modified cells
immediately, without first doing a large memcpy(3).

In worst case scenarios (or perhaps we should consider them best case
scenarios...), I've seen up to a 10x performance increase in frame
rendering times (this obviously does *not* include the time it takes
to copy over the previous frame's damage, since that doesn't affect
neither input processing nor frame rendering).

Implemented by adding a callback mechanism to the shm abstraction
layer. Use it for the grid buffers, and kick off a thread that copies
the previous frame's damage, and resets the buffers age to 0 (so that
foot understands it can start render to it immediately when it later
needs to render a frame).

Since we have certain way of knowing if a compositor releases buffers
immediately or not, use a bit of heuristics; if we see 10 consecutive
non-immediate releases (that is, we reset the counter as soon as we do
see an immediate release), this new "pre-apply damage" logic is
enabled. It can be force-disabled with tweak.pre-apply-damage=no.

We also need to take care to wait for the thread before resetting the
render's "last_buf" pointer (or we'll SEGFAULT in the thread...).

We must also ensure we wait for the thread to finish before we start
rendering a new frame. Under normal circumstances, the wait time is
always 0, the thread has almost always finished long before we need to
render the next frame. But it _can_ happen.

Closes #2188
2025-10-10 10:23:17 +02:00

51 lines
1.4 KiB
C

#pragma once
#include <stdbool.h>
#include "terminal.h"
#include "fdm.h"
#include "wayland.h"
#include "misc.h"
struct renderer;
struct renderer *render_init(struct fdm *fdm, struct wayland *wayl);
void render_destroy(struct renderer *renderer);
enum resize_options {
RESIZE_NORMAL = 0,
RESIZE_FORCE = 1 << 0,
RESIZE_BY_CELLS = 1 << 1,
RESIZE_KEEP_GRID = 1 << 2,
};
bool render_resize(
struct terminal *term, int width, int height, uint8_t resize_options);
void render_refresh(struct terminal *term);
void render_refresh_app_id(struct terminal *term);
void render_refresh_icon(struct terminal *term);
void render_refresh_csd(struct terminal *term);
void render_refresh_search(struct terminal *term);
void render_refresh_title(struct terminal *term);
void render_refresh_urls(struct terminal *term);
bool render_xcursor_set(
struct seat *seat, struct terminal *term, enum cursor_shape shape);
bool render_xcursor_is_valid(const struct seat *seat, const char *cursor);
void render_overlay(struct terminal *term);
struct render_worker_context {
int my_id;
struct terminal *term;
};
int render_worker_thread(void *_ctx);
struct csd_data {
int x;
int y;
int width;
int height;
};
struct csd_data get_csd_data(const struct terminal *term, enum csd_surface surf_idx);
void render_buffer_release_callback(struct buffer *buf, void *data);