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render: gamma-correct blending

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This implements gamma-correct blending, which mainly affects font
rendering.

The implementation requires compile-time availability of the new
color-management protocol (available in wayland-protocols >= 1.41),
and run-time support for the same in the compositor (specifically, the
EXT_LINEAR TF function and sRGB primaries).

How it works: all colors are decoded from sRGB to linear (using a
lookup table, generated in the exact same way pixman generates it's
internal conversion tables) before being used by pixman. The resulting
image buffer is thus in decoded/linear format. We use the
color-management protocol to inform the compositor of this, by tagging
the wayland surfaces with the 'ext_linear' image attribute.

Sixes: all colors are sRGB internally, and decoded to linear before
being used in any sixels. Thus, the image buffers will contain linear
colors. This is important, since otherwise there would be a
decode/encode penalty every time a sixel is blended to the grid.

Emojis: we require fcft >= 3.2, which adds support for sRGB decoding
color glyphs. Meaning, the emoji pixman surfaces can be blended
directly to the grid, just like sixels.

Gamma-correct blending is enabled by default *when the compositor
supports it*. There's a new option to explicitly enable/disable it:
gamma-correct-blending=no|yes. If set to 'yes', and the compositor
does not implement the required color-management features, warning
logs are emitted.

There's a loss of precision when storing linear pixels in 8-bit
channels. For this reason, this patch also adds supports for 10-bit
surfaces. For now, this is disabled by default since such surfaces
only have 2 bits for alpha. It can be enabled with
tweak.surface-bit-depth=10-bit.

Perhaps, in the future, we can enable it by default if:

* gamma-correct blending is enabled
* the user has not enabled a transparent background
This commit is contained in:
Daniel Eklöf 2025-02-21 11:01:29 +01:00
parent 6d39f66eb7
commit ccf625b991
No known key found for this signature in database
GPG key ID: 5BBD4992C116573F
20 changed files with 746 additions and 101 deletions
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80
shm.c
View file

@ -92,6 +92,12 @@ struct buffer_chain {
struct wl_shm *shm;
size_t pix_instances;
bool scrollable;
pixman_format_code_t pixman_fmt_without_alpha;
enum wl_shm_format shm_format_without_alpha;
pixman_format_code_t pixman_fmt_with_alpha;
enum wl_shm_format shm_format_with_alpha;
};
static tll(struct buffer_private *) deferred;
@ -115,6 +121,7 @@ buffer_destroy_dont_close(struct buffer *buf)
if (buf->pix[i] != NULL)
pixman_image_unref(buf->pix[i]);
}
if (buf->wl_buf != NULL)
wl_buffer_destroy(buf->wl_buf);
@ -262,7 +269,9 @@ instantiate_offset(struct buffer_private *buf, off_t new_offset)
wl_buf = wl_shm_pool_create_buffer(
pool->wl_pool, new_offset,
buf->public.width, buf->public.height, buf->public.stride,
buf->with_alpha ? WL_SHM_FORMAT_ARGB8888 : WL_SHM_FORMAT_XRGB8888);
buf->with_alpha
? buf->chain->shm_format_with_alpha
: buf->chain->shm_format_without_alpha);
if (wl_buf == NULL) {
LOG_ERR("failed to create SHM buffer");
@ -272,9 +281,12 @@ instantiate_offset(struct buffer_private *buf, off_t new_offset)
/* One pixman image for each worker thread (do we really need multiple?) */
for (size_t i = 0; i < buf->public.pix_instances; i++) {
pix[i] = pixman_image_create_bits_no_clear(
buf->with_alpha ? PIXMAN_a8r8g8b8 : PIXMAN_x8r8g8b8,
buf->with_alpha
? buf->chain->pixman_fmt_with_alpha
: buf->chain->pixman_fmt_without_alpha,
buf->public.width, buf->public.height,
(uint32_t *)mmapped, buf->public.stride);
if (pix[i] == NULL) {
LOG_ERR("failed to create pixman image");
goto err;
@ -959,14 +971,74 @@ shm_unref(struct buffer *_buf)
}
struct buffer_chain *
shm_chain_new(struct wl_shm *shm, bool scrollable, size_t pix_instances)
shm_chain_new(struct wayland *wayl, bool scrollable, size_t pix_instances,
bool ten_bit_if_capable)
{
pixman_format_code_t pixman_fmt_without_alpha = PIXMAN_x8r8g8b8;
enum wl_shm_format shm_fmt_without_alpha = WL_SHM_FORMAT_XRGB8888;
pixman_format_code_t pixman_fmt_with_alpha = PIXMAN_a8r8g8b8;
enum wl_shm_format shm_fmt_with_alpha = WL_SHM_FORMAT_ARGB8888;
static bool have_logged = false;
if (ten_bit_if_capable) {
if (wayl->shm_have_argb2101010 && wayl->shm_have_xrgb2101010) {
pixman_fmt_without_alpha = PIXMAN_x2r10g10b10;
shm_fmt_without_alpha = WL_SHM_FORMAT_XRGB2101010;
pixman_fmt_with_alpha = PIXMAN_a2r10g10b10;
shm_fmt_with_alpha = WL_SHM_FORMAT_ARGB2101010;
if (!have_logged) {
have_logged = true;
LOG_INFO("using 10-bit RGB surfaces");
}
}
else if (wayl->shm_have_abgr2101010 && wayl->shm_have_xbgr2101010) {
pixman_fmt_without_alpha = PIXMAN_x2b10g10r10;
shm_fmt_without_alpha = WL_SHM_FORMAT_XBGR2101010;
pixman_fmt_with_alpha = PIXMAN_a2b10g10r10;
shm_fmt_with_alpha = WL_SHM_FORMAT_ABGR2101010;
if (!have_logged) {
have_logged = true;
LOG_INFO("using 10-bit BGR surfaces");
}
}
else {
if (!have_logged) {
have_logged = true;
LOG_WARN(
"10-bit surfaces requested, but compositor does not "
"implement ARGB2101010+XRGB2101010, or "
"ABGR2101010+XBGR2101010. Falling back to 8-bit surfaces");
}
}
} else {
if (!have_logged) {
have_logged = true;
LOG_INFO("using 8-bit RGB surfaces");
}
}
struct buffer_chain *chain = xmalloc(sizeof(*chain));
*chain = (struct buffer_chain){
.bufs = tll_init(),
.shm = shm,
.shm = wayl->shm,
.pix_instances = pix_instances,
.scrollable = scrollable,
.pixman_fmt_without_alpha = pixman_fmt_without_alpha,
.shm_format_without_alpha = shm_fmt_without_alpha,
.pixman_fmt_with_alpha = pixman_fmt_with_alpha,
.shm_format_with_alpha = shm_fmt_with_alpha,
};
return chain;
}