diff options
Diffstat (limited to 'libass/ass_render.c')
| -rw-r--r-- | libass/ass_render.c | 19 |
1 files changed, 15 insertions, 4 deletions
diff --git a/libass/ass_render.c b/libass/ass_render.c index 50135de00c..327f886b19 100644 --- a/libass/ass_render.c +++ b/libass/ass_render.c @@ -570,6 +570,17 @@ static void change_alpha(uint32_t* var, uint32_t new, double pwr) *var = (_r(*var) << 24) + (_g(*var) << 16) + (_b(*var) << 8) + (_a(*var) * (1 - pwr) + _a(new) * pwr); } +/** + * \brief Multiply two alpha values + * \param a first value + * \param b second value + * \return result of multiplication + * Parameters and result are limited by 0xFF. + */ +static uint32_t mult_alpha(uint32_t a, uint32_t b) +{ + return 0xFF - (0xFF - a) * (0xFF - b) / 0xFF; +} /** * \brief Calculate alpha value by piecewise linear function @@ -596,10 +607,10 @@ static void interpolate_alpha(long long now, } - change_alpha(&render_context.c1, a, 1.); - change_alpha(&render_context.c2, a, 1.); - change_alpha(&render_context.c3, a, 1.); - change_alpha(&render_context.c4, a, 1.); + change_alpha(&render_context.c1, mult_alpha(_a(render_context.c1), a), 1.); + change_alpha(&render_context.c2, mult_alpha(_a(render_context.c2), a), 1.); + change_alpha(&render_context.c3, mult_alpha(_a(render_context.c3), a), 1.); + change_alpha(&render_context.c4, mult_alpha(_a(render_context.c4), a), 1.); } /** |