Another question arises: why do we divide by ras.conic_level when we are
dealing with cubic splines? Surely it should be
dx = dx / ras.cubic_level;
or (better - we can use assignment operators in FreeType, I think ;-):
dx /= ras.cubic_level;
Graham
Werner LEMBERG wrote:
Calculate the midpoint and compare it with start and end: [...]
For me, this looks good. Thanks for working on this.
I am sceptical about the need to calculate both da and db. Perhaps
db only will suffice. I hope that David or Werner can comment.
This is something Ken can probably check: He has a large database for
Ghostscript to compare rendering results, and artifacts introduced by
the simplified shorthand calculation would easily show up, I think.
Below is a patch according to your data (hopefully, I've understood
you correctly). Please check and test.
Werner
======================================================================
--- ftgrays.c.orig 2009-07-31 18:45:19.000000000 +0200
+++ ftgrays.c 2010-06-08 09:56:23.000000000 +0200
@@ -1007,45 +1007,40 @@
const FT_Vector* control2,
const FT_Vector* to )
{
- TPos dx, dy, da, db;
+ TPos dx, dy;
+ TPos mid_x, mid_y;
int top, level;
int* levels;
FT_Vector* arc;
- dx = DOWNSCALE( ras.x ) + to->x - ( control1->x << 1 );
- if ( dx < 0 )
- dx = -dx;
- dy = DOWNSCALE( ras.y ) + to->y - ( control1->y << 1 );
- if ( dy < 0 )
- dy = -dy;
- if ( dx < dy )
- dx = dy;
- da = dx;
+ /* Calculate midpoint and compare it with start and end. */
+ mid_x = ( DOWNSCALE( ras.x ) + to->x +
+ 3 * ( control1->x + control2->x ) ) / 8;
+ mid_y = ( DOWNSCALE( ras.y ) + to->y +
+ 3 * ( control1->y + control2->y ) ) / 8;
- dx = DOWNSCALE( ras.x ) + to->x - 3 * ( control1->x + control2->x );
+ dx = DOWNSCALE( ras.x ) + to->x - ( mid_x << 1 );
if ( dx < 0 )
dx = -dx;
- dy = DOWNSCALE( ras.y ) + to->y - 3 * ( control1->x + control2->y );
+ dy = DOWNSCALE( ras.y ) + to->y - ( mid_y << 1 );
if ( dy < 0 )
dy = -dy;
if ( dx < dy )
dx = dy;
- db = dx;
+ /* Check whether an approximation with straight lines is sufficient. */
level = 1;
- da = da / ras.cubic_level;
- db = db / ras.conic_level;
- while ( da > 0 || db > 0 )
+ dx = dx / ras.conic_level;
+ while ( dx > 0 )
{
- da >>= 2;
- db >>= 3;
+ dx >>= 3;
level++;
}
if ( level <= 1 )
{
- TPos to_x, to_y, mid_x, mid_y;
+ TPos to_x, to_y;
to_x = UPSCALE( to->x );
@@ -1104,7 +1099,7 @@
Draw:
{
- TPos to_x, to_y, mid_x, mid_y;
+ TPos to_x, to_y;
to_x = arc[0].x;
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