diff options
| author | Robin Watts <robin.watts@artifex.com> | 2016-10-06 19:51:29 +0100 |
|---|---|---|
| committer | Robin Watts <robin.watts@artifex.com> | 2016-10-07 16:56:46 +0100 |
| commit | c5f8d745e4dc42404409a2c166181d85bc87934b (patch) | |
| tree | 1ff341b87b3891a998aba07fb3699b1dd4148ce4 /include | |
| parent | 7836643e0d6e9cc8e9d0d5c71cbfac5ee772ae21 (diff) | |
| download | mupdf-c5f8d745e4dc42404409a2c166181d85bc87934b.tar.xz | |
Correct maths error in painters.
As part of the blending calculations, we do:
dst = src * mask_alpha + dst * (1-mask_alpha.src_alpha)
We calculate mask_alpha as ma, and 1-mask_alpha.src_alpha as masa.
In full accuracy, we should never have ma + masa >= 1.
Unfortunately, with the formulation used in the painters at the
moment, we can. We therefore rejig the calculations slightly.
Diffstat (limited to 'include')
| -rw-r--r-- | include/mupdf/fitz/math.h | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/include/mupdf/fitz/math.h b/include/mupdf/fitz/math.h index 9ba79697..5e25f871 100644 --- a/include/mupdf/fitz/math.h +++ b/include/mupdf/fitz/math.h @@ -19,6 +19,11 @@ static inline int fz_mul255(int a, int b) * to give a single value in the same range as A was. */ #define FZ_COMBINE(A,B) (((A)*(B))>>8) +/* Combine values A (in the 0..255 range) and B (in the 0..256 range), + * then reverse it within that range to give a single value in the + * 0..256 range. */ +#define FZ_REVERSE_COMBINE(A,B) ((0xFF00 - (A)*(B))>>8) + /* Combine values A and C (in the same (any) range) and B and D (in the * 0..256 range), to give a single value in the same range as A and C were. */ #define FZ_COMBINE2(A,B,C,D) (FZ_COMBINE((A), (B)) + FZ_COMBINE((C), (D))) |