diff options
Diffstat (limited to 'src/xine-engine/alphablend.c')
| -rw-r--r-- | src/xine-engine/alphablend.c | 55 |
1 files changed, 48 insertions, 7 deletions
diff --git a/src/xine-engine/alphablend.c b/src/xine-engine/alphablend.c index 2e3af5422..25c223272 100644 --- a/src/xine-engine/alphablend.c +++ b/src/xine-engine/alphablend.c @@ -1052,8 +1052,7 @@ static void mem_blend8(uint8_t *mem, uint8_t val, uint8_t o, size_t sz) } } -static void blend_yuv_exact(uint8_t *dst_cr, uint8_t *dst_cb, - int src_width, int x_odd, +static void blend_yuv_exact(uint8_t *dst_cr, uint8_t *dst_cb, int src_width, uint8_t *(*blend_yuv_data)[ 3 ][ 2 ]) { int x; @@ -1091,6 +1090,7 @@ static void blend_yuv_exact(uint8_t *dst_cr, uint8_t *dst_cb, int t4 = 4*0xf - o; /* blend the output chroma to the average of the four pixels */ + /* for explanation of the used equation, see blend_yuy2_exact() */ *dst_cr = ((*dst_cr * t4 + cr00 * o00 + cr01 * o01 + cr10 * o10 + cr11 * o11) * (0x1111+1)) >> 18; *dst_cb = ((*dst_cb * t4 + cb00 * o00 + cb01 * o01 + cb10 * o10 + cb11 * o11) * (0x1111+1)) >> 18; } @@ -1431,7 +1431,7 @@ void _x_blend_yuv (uint8_t *dst_base[3], vo_overlay_t * img_overl, memset(&(*blend_yuv_data)[ 0 ][ 1 ][ 0 ], 0, exact_blend_width_m2); } - blend_yuv_exact(dst_cr, dst_cb, exact_blend_width, x_odd, blend_yuv_data); + blend_yuv_exact(dst_cr, dst_cb, exact_blend_width, blend_yuv_data); any_line_buffered = 0; } @@ -1452,7 +1452,7 @@ void _x_blend_yuv (uint8_t *dst_base[3], vo_overlay_t * img_overl, memset(&(*blend_yuv_data)[ 0 ][ 1 ][ 0 ], 0, exact_blend_width_m2); } - blend_yuv_exact(dst_cr, dst_cb, exact_blend_width, x_odd, blend_yuv_data); + blend_yuv_exact(dst_cr, dst_cb, exact_blend_width, blend_yuv_data); } } @@ -1461,8 +1461,7 @@ void _x_blend_yuv (uint8_t *dst_base[3], vo_overlay_t * img_overl, #endif } -static void blend_yuy2_exact(uint8_t *dst_cr, uint8_t *dst_cb, - int src_width, int x_odd, +static void blend_yuy2_exact(uint8_t *dst_cr, uint8_t *dst_cb, int src_width, uint8_t *(*blend_yuy2_data)[ 3 ]) { int x; @@ -1491,7 +1490,49 @@ static void blend_yuy2_exact(uint8_t *dst_cr, uint8_t *dst_cb, /* calculate transparency of background over the two pixels */ int t2 = 2*0xf - o; + /* + * No need to adjust chroma values with +/- 128: + * *dst_cb + * = 128 + ((*dst_cb-128) * t2 + (cb0-128) * o0 + (cb1-128) * o1) / (2 * 0xf); + * = 128 + (*dst_cb * t2 + cb0 * o0 + cb1 * o1 + (t2*(-128) - 128*o0 - 128*o1)) / (2 * 0xf); + * = 128 + (*dst_cb * t2 + cb0 * o0 + cb1 * o1 + ((2*0xf-o0-o1)*(-128) - 128*o0 - 128*o1)) / (2 * 0xf); + * = 128 + (*dst_cb * t2 + cb0 * o0 + cb1 * o1 + (2*0xf*(-128))) / (2 * 0xf); + * = 128 + (*dst_cb * t2 + cb0 * o0 + cb1 * o1) / (2 * 0xf) - 128; + * = (*dst_cb * t2 + cb0 * o0 + cb1 * o1) / (2 * 0xf); + * + * Convert slow divisions to multiplication and shift: + * X/0xf + * = X * (1/0xf) + * = X * (0x1111/0x1111) * (1/0xf) + * = X * 0x1111/0xffff + * =(almost) X * 0x1112/0x10000 + * = (X * 0x1112) >> 16 + * + * The tricky point is 0x1111/0xffff --> 0x1112/0x10000. + * All calculations are done using integers and X is in + * range of [0 ... 0xff*0xf*4]. This results in error of + * X*0x1112/0x10000 - X/0xf + * = X*(0x1112/0x10000 - 1/0xf) + * = X*(0x0.1112 - 0x0.111111...) + * = X*0.0000eeeeee.... + * = [0 ... 0.37c803fc...] when X in [0...3bc4] + * As the error is less than 1 and always positive, whole error + * "disappears" during truncation (>>16). Rounding to exact results is + * guaranteed by selecting 0x1112 instead of more accurate 0x1111 + * (with 0x1111 error=X*(-0.00001111...)). With 0x1112 error is + * always positive, but still less than one. + * So, one can forget the "=(almost)" as it is really "=" when source + * operands are within 0...0xff (U,V) and 0...0xf (A). + * + * 1/0x10000 (= >>16) was originally selected because of MMX pmullhw + * instruction; it makes possible to do whole calculation in MMX using + * uint16's (pmullhw is (X*Y)>>16). + * + * Here X/(2*0xf) = X/0xf/2 = ((X*0x1112)>>16)>>1 = (X*0x1112)>>17 + */ + /* blend the output chroma to the average of the two pixels */ + /* *dst_cr = 128 + ((*dst_cr-128) * t2 + (cr0-128) * o0 + (cr1-128) * o1) / (2 * 0xf); */ *dst_cr = ((*dst_cr * t2 + cr0 * o0 + cr1 * o1) * (0x1111+1)) >> 17; *dst_cb = ((*dst_cb * t2 + cb0 * o0 + cb1 * o1) * (0x1111+1)) >> 17; } @@ -1837,7 +1878,7 @@ void _x_blend_yuy2 (uint8_t * dst_img, vo_overlay_t * img_overl, if (enable_exact_blending) { /* blend buffered line */ if (any_line_buffered) { - blend_yuy2_exact(dst_y - x_odd * 2 + 3, dst_y - x_odd * 2 + 1, exact_blend_width, x_odd, blend_yuy2_data); + blend_yuy2_exact(dst_y - x_odd * 2 + 3, dst_y - x_odd * 2 + 1, exact_blend_width, blend_yuy2_data); any_line_buffered = 0; } |