AuroraMiddleware/skia2
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

add comments for computing derivatives

Browse Source 
git-svn-id: http://skia.googlecode.com/svn/trunk@8711 2bbb7eff-a529-9590-31e7-b0007b416f81
This commit is contained in:
reed@google.com 2013-04-16 21:07:27 +00:00
parent 63cd3c6406
commit 17a2c919d0
1 changed files with 37 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
src/core/SkGeometry.cpp
View File

@ -1401,6 +1401,43 @@ static SkScalar eval_ratquad(const SkScalar src[], SkScalar w, SkScalar t) {
return SkScalarDiv(numer, denom);
}
#if 0
// F = (A (1 - t)^2 + C t^2 + 2 B (1 - t) t w)
// ------------------------------------------
// ((1 - t)^2 + t^2 + 2 (1 - t) t w)
//
// = {t^2 (P0 + P2 - 2 P1 w), t (-2 P0 + 2 P1 w), P0}
// ------------------------------------------------
// {t^2 (2 - 2 w), t (-2 + 2 w), 1}
//
// F' = 2 (C t (1 + t (-1 + w)) - A (-1 + t) (t (-1 + w) - w) + B (1 - 2 t) w)
//
// {t^2 (2 P0 - 2 P2 - 2 P0 w + 2 P2 w), t (-2 P0 + 2 P2 + 4 P0 w - 4 P1 w), -2 P0 w + 2 P1 w}
//
// Take the parametric specification for the conic (either X or Y) and return
// in coeff[] the coefficients for the simple quadratic polynomial
// coeff[0] for t^2
// coeff[1] for t
// coeff[2] for constant term
//
static void conic_numer_coeff(const SkScalar src[], SkScalar w, SkScalar coeff[3]) {
coeff[0] = src[0] + src[4] - 2 * src[2] * w;
coeff[1] = 2 * (src[2] * w - src[0]);
coeff[0] = src[0];
}
// coeff[0] for t^2
// coeff[1] for t
// coeff[2] for constant term
//
static void conic_deriv_coeff(const SkScalar src[], SkScalar w, SkScalar coeff[3]) {
coeff[0] = 2 * (src[0] - src[2] + w * (src[4] - src[0]));
coeff[1] = 2 (src[4] - src[0] + 2 * w * (src[0] - src[2]));
coeff[2] = 2 * w * (src[2] - src[0]);
}
#endif
struct SkP3D {
SkScalar fX, fY, fZ;