Commit fb09a51f0f6b57b8110ae1ada81c48adc968b4c2
2013-08-04T18:24:02
Add comments to `ft_corner_is_flat'.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55
diff --git a/src/base/ftcalc.c b/src/base/ftcalc.c
index 0ec0d78..c02daa4 100644
--- a/src/base/ftcalc.c
+++ b/src/base/ftcalc.c
@@ -945,11 +945,27 @@
FT_Pos d_in, d_out, d_corner;
+ /* We approximate the Euclidean metric (sqrt(x^2 + y^2)) with */
+ /* the Taxicab metric (x + y), which can be computed much */
+ /* faster. If one of the two vectors is much longer than the */
+ /* other one, the direction of the shorter vector doesn't */
+ /* influence the result any more. */
+ /* */
+ /* corner */
+ /* x---------------------------x */
+ /* \ / */
+ /* \ / */
+ /* in \ / out */
+ /* \ / */
+ /* o */
+ /* Point */
+ /* */
+
if ( ax < 0 )
ax = -ax;
if ( ay < 0 )
ay = -ay;
- d_in = ax + ay;
+ d_in = ax + ay; /* d_in = || in || */
ax = out_x;
if ( ax < 0 )
@@ -957,7 +973,7 @@
ay = out_y;
if ( ay < 0 )
ay = -ay;
- d_out = ax + ay;
+ d_out = ax + ay; /* d_out = || out || */
ax = out_x + in_x;
if ( ax < 0 )
@@ -965,7 +981,11 @@
ay = out_y + in_y;
if ( ay < 0 )
ay = -ay;
- d_corner = ax + ay;
+ d_corner = ax + ay; /* d_corner = || in + out || */
+
+ /* now do a simple length comparison: */
+ /* */
+ /* d_in + d_out < 17/16 d_corner */
return ( d_in + d_out - d_corner ) < ( d_corner >> 4 );
}