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| author | Přemysl Eric Janouch <p@janouch.name> | 2021-12-15 03:24:05 +0100 |
|---|---|---|
| committer | Přemysl Eric Janouch <p@janouch.name> | 2021-12-15 03:43:57 +0100 |
| commit | 7297c40f93763597af43e25e04650159e7a13597 (patch) | |
| tree | ae8c41f3ccf30b14ae34a446806a2fcd822de1b6 | |
| parent | ea2d159773c55575c6b1ea2fa76f6dd4c4883499 (diff) | |
| download | fiv-7297c40f93763597af43e25e04650159e7a13597.tar.gz fiv-7297c40f93763597af43e25e04650159e7a13597.tar.xz fiv-7297c40f93763597af43e25e04650159e7a13597.zip | |
Employ libwebp's alpha premultiplication
It seems to perform roughly equally in optimized builds.
| -rw-r--r-- | fastiv-io.c | 18 |
1 files changed, 10 insertions, 8 deletions
diff --git a/fastiv-io.c b/fastiv-io.c index 67041d3..33ff9b8 100644 --- a/fastiv-io.c +++ b/fastiv-io.c @@ -162,6 +162,9 @@ try_append_page(cairo_surface_t *surface, cairo_surface_t **result, // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +// From libwebp, verified to exactly match [x * a / 255]. +#define PREMULTIPLY8(a, x) (((uint32_t) (x) * (uint32_t) (a) * 32897U) >> 23) + static bool pull_passthrough(const wuffs_base__more_information *minfo, wuffs_base__io_buffer *src, wuffs_base__io_buffer *dst, GError **error) @@ -1375,12 +1378,11 @@ load_libheif_image(struct heif_image_handle *handle, GError **error) for (int y = 0; y < h; y++) { uint32_t *dstp = (uint32_t *) (dst + dst_stride * y); for (int x = 0; x < w; x++) { - uint32_t pixel = dstp[x], a = pixel >> 24; - uint8_t r = pixel >> 16; - uint8_t g = pixel >> 8; - uint8_t b = pixel; + uint32_t argb = dstp[x], a = argb >> 24; dstp[x] = a << 24 | - (r * a / 255) << 16 | (g * a / 255) << 8 | (b * a / 255); + PREMULTIPLY8(a, 0xFF & (argb >> 16)) << 16 | + PREMULTIPLY8(a, 0xFF & (argb >> 8)) << 8 | + PREMULTIPLY8(a, 0xFF & argb); } } } @@ -2361,9 +2363,9 @@ read_spng_thumbnail( for (size_t i = size / sizeof *data; i--; ) { const uint8_t *unit = (const uint8_t *) &data[i]; uint32_t a = unit[3], - b = unit[2] * a / 255, - g = unit[1] * a / 255, - r = unit[0] * a / 255; + b = PREMULTIPLY8(a, unit[2]), + g = PREMULTIPLY8(a, unit[1]), + r = PREMULTIPLY8(a, unit[0]); data[i] = a << 24 | r << 16 | g << 8 | b; } } else { |