David,
I've tested your code with CartoType, my map rendering library, and it
produces a small speedup there too. (The smallness of the speedup is to
do with the fact that CartoType's curves are nearly always
approximations to arcs of circles, which don't behave too badly with my
previous optimisation; I can see why your code works better with font
glyphs.)
Therefore, combined with the fact that it significantly speeds up font
rendering, and solves the bug that prompted this latest burst of work, I
recommend that it goes into FreeType.
Werner, can you give a ruling on whether assignments in conditionals are
allowed in FreeType code?
David, what value are you using for FT_MAX_CURVE_DEVIATION? I assume 16,
which is a good conservative value.
The full patch also requires getting rid of the now-unneeded cubic-level
and conic-level variables, and making minor changes to the conic
splitting routine. However, we could perhaps make the change to cubic
splitting independent of any changes to conic splitting, because the
latter doesn't suffer from the original bug ('if it ain't broke don't
fix it').
Best regards,
Graham
On 08/09/2010 08:50, David Bevan wrote:
Graham,
Here's a final revision.
It produces exactly the same results as the previous one but the code is a bit
faster (and also easier to understand - the previous code was trying to be a
bit too clever).
David %^
static void
gray_render_cubic( RAS_ARG_ const FT_Vector* control1,
const FT_Vector* control2,
const FT_Vector* to )
{
FT_Vector* arc;
arc = ras.bez_stack;
arc[0].x = UPSCALE( to-x );
arc[0].y = UPSCALE( to-y );
arc[1].x = UPSCALE( control2-x );
arc[1].y = UPSCALE( control2-y );
arc[2].x = UPSCALE( control1-x );
arc[2].y = UPSCALE( control1-y );
arc[3].x = ras.x;
arc[3].y = ras.y;
for (;;)
{
/* Check that the arc crosses the current band. */
TPos min, max, y;
min = max = arc[0].y;
y = arc[1].y;
if ( y min ) min = y;
if ( y max ) max = y;
y = arc[2].y;
if ( y min ) min = y;
if ( y max ) max = y;
y = arc[3].y;
if ( y min ) min = y;
if ( y max ) max = y;
if ( TRUNC( min )= ras.max_ey || TRUNC( max ) 0 )
goto Draw;
/* Decide whether to split or draw */
/* See Hain's paper at http://tinyurl.com/HainBez for more info */
{
TPos dx, dy, L, dx1, dy1, dx2, dy2, s, s_limit;
/* dx and dy are x- and y- components of the P0-P3 chord vector */
dx = arc[3].x - arc[0].x;
dy = arc[3].y - arc[0].y;
/* L is an (under)estimate of the Euclidean distance P0-P3 */
L = ( 236 * FT_MAX(labs(dx), labs(dy))
+ 97 * FT_MIN(labs(dx), labs(dy))) 8;
/* avoid possible arithmetic overflow below by splitting */
if (L 32767)
goto Split;
/* s is L * the perpendicular distance from P1 to the line P0-P3 */
s = labs( dy * (dx1 = arc[1].x - arc[0].x)
- dx * (dy1 = arc[1].y - arc[0].y));
/* max deviation may be as much as (s/L) * 3/4 (if Hain's v = 1) */
if (s (s_limit = L * (TPos)(FT_MAX_CURVE_DEVIATION / 0.75)))
goto Split;
/* s is L * the perpendicular distance from P2 to the line P0-P3 */
s = labs( dy * (dx2 = arc[2].x - arc[0].x)
- dx * (dy2 = arc[2].y - arc[0].y));
/* max deviation may be as much as (s/L) * 3/4 (if Hain's v = 1) */
if (s s_limit)
goto Split;
/* if P1 or P2 is outside P0-P3, split */
if ( dy * dy1 + dx * dx1 0
|| dy * dy2 + dx * dx2 0
|| dy * (arc[3].y - arc[1].y) + dx * (arc[3].x - arc[1].x) 0
|| dy * (arc[3].y - arc[2].y) + dx * (arc[3].x - arc[2].x) 0
)
goto Split;
/* no reason to split */
goto Draw;
}
Split:
gray_split_cubic( arc );
arc += 3;
continue;
Draw:
gray_render_line( RAS_VAR_ arc[0].x, arc[0].y );
if (arc == ras.bez_stack)
return;
arc -= 3;
}
}
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