7:45 a.m.
This is sort of a follow up question to my previous one about circles.
Is there in 2geom a set of methods along the lines of:
isRect(path)
isTriangle(path)
isLine(path)
which return true if the path has the specified geometry?
I need the first one and don't want to reinvent the wheel.
Thanks,
David Mathog
mathog@...1176...
Manager, Sequence Analysis Facility, Biology Division, Caltech
7:52 a.m.
New subject: [Inkscape-devel] recognizing rectangles, lines, etc. in 2geom, like "isrect()"???
On 16-Dec-2013 14:45, mathog wrote:
This is sort of a follow up question to my previous one about
circles.
Is there in 2geom a set of methods along the lines of:
isRect(path)
Note that isRect() should be true for both
(0,0)
(100,0)
(100,20)
(0,20)
and
(0,0)
(100,0)
(100,5)
(100,15)
(100,20)
(0,20)
That is the path has the geometry specified, but it need not be have the
minimum number of points.
(However if it doesn't have the minimum number of points then I am also
going to need something like:
Geom::PathVector vertices = RectVertices(path);
)
Thanks,
David Mathog
mathog@...1176...
Manager, Sequence Analysis Facility, Biology Division, Caltech
7:55 a.m.
New subject: [Inkscape-devel] recognizing rectangles, lines, etc. in 2geom, like "isrect()"???
On 16-Dec-2013 14:52, mathog wrote:
On 16-Dec-2013 14:45, mathog wrote:
> This is sort of a follow up question to my previous one about circles.
> Is there in 2geom a set of methods along the lines of:
>
> isRect(path)
Note that isRect() should be true for both
In the patch for bug 1263242 here
https://bugs.launchpad.net/inkscape/+bug/1263242
these 3 functions were added to emf-print.cpp.
Geom::Path pathv_to_simple_polygon(Geom::PathVector const &pathv,
int *vertices);
Geom::Path pathv_to_rect(Geom::PathVector const &pathv, bool
*is_rect, double *angle);
Geom::Point get_pathrect_corner(Geom::Path pathRect, double angle,
int corner);
They probably should be in src/helper/geom.cpp, but at the moment the
only code that uses them
is in emf-print.cpp, so there they are. (The names are maybe not
exactly right for what these do.)
The first function returns a path in which any points on a polygonal
path (stored in a PathVector) that are not at a vertex have been
eliminated. It also eliminates one point where two fall within epsilon
of each other. (Duplicate points, not sure what the technical
term for them is.) If the pathvector holds more than one path or has
any curves that are not linear then it returns an empty path.
The second analyzes a PathVector to see if it is a rectangle. It does
this by first calling
the preceding function, then checking that the path has 4 sides and that
each side is 90 degrees from its two neighbors. If that is the case
is_rect comes back true. The angle returned is that of the minimal
rotation that will align the sides of the rectangle with the X and Y
axes.
The third returns the coordinates of the Upper Left, Upper Right, Lower
Right, and Lower Left corners of the rectangle, as determined by the
value of "corner", given the rotation angle and path returned by the
preceding function.
It would not surprise me to learn that these functions are already
somewhere in Inkscape, but when I looked I could not find them.
Regards,
David Mathog
mathog@...1176...
Manager, Sequence Analysis Facility, Biology Division, Caltech
9:32 a.m.
Hi David,
On Fri, Dec 20, 2013 at 02:55:00PM -0800, mathog wrote:
In the patch for bug 1263242 here
https://bugs.launchpad.net/inkscape/+bug/1263242
I can't work out how to get to your patch from this link.
these 3 functions were added to emf-print.cpp.
Geom::Path pathv_to_simple_polygon(Geom::PathVector const &pathv,
int *vertices);
Geom::Path pathv_to_rect(Geom::PathVector const &pathv, bool
*is_rect, double *angle);
Geom::Point get_pathrect_corner(Geom::Path pathRect, double angle,
int corner);
The first function returns a path in which any points on a polygonal
path (stored in a PathVector) that are not at a vertex have been
eliminated. It also eliminates one point where two fall within epsilon
of each other. (Duplicate points, not sure what the technical
term for them is.) If the pathvector holds more than one path or has
any curves that are not linear then it returns an empty path.
This name is not quite ideal, a simple polygon is one which also has
no self intersections, something you don't guarantee. Perhaps
describe what it does: remove_superfluous_vertices ?
The second analyzes a PathVector to see if it is a rectangle. It
does
this by first calling
the preceding function, then checking that the path has 4 sides and that
each side is 90 degrees from its two neighbors. If that is the case
is_rect comes back true. The angle returned is that of the minimal
rotation that will align the sides of the rectangle with the X and Y
axes.
Sounds good, definitely could go in 2geom.
The third returns the coordinates of the Upper Left, Upper Right,
Lower
Right, and Lower Left corners of the rectangle, as determined by the
value of "corner", given the rotation angle and path returned by the
preceding function.
You might construct this using the Rect::corner function combined with
multiplication by a rotation.
njh
10:18 a.m.
I prefer to declare variables as I use them, but I can't remember what
style the code uses. Can you check please.
+ if(Geom::are_near(dot(v1,v2),1.0)){ // P1 is within a straight line
I would use cross here, which is more numerically stable in this case
because it has error that is linear rather than quadratic with
divergences (I think).
+ if(Geom::are_near(cross(v1,v2),0.0)){ // P1 is within a straight line
Can you fix the spacing up to match the code - you've go a somewhat
arbitrary mix of no space, single space and double space around
operators.
Other than that, it looks fine.
njh
4:33 a.m.
New subject: recognizing rectangles, lines, etc. in 2geom, like "isrect()"???
On 21 Dec 2013, at 02:18, Nathan Hurst <njh@...1927...> wrote:
I prefer to declare variables as I use them, but I can't remember
what
style the code uses.
Yes, we define variables at the point where we need them, so we know how to initialize
them meaningfully. I find it makes for hard to maintain code to define variables up front
(especially without meaningful initialization).
<rant, please skip>
It is 2013, and it is fine to write C99 (or newer) code. And because Inkscape and 2Geom
are C++, one should use that language, i.e. not define all variables at start of scope.
One thing that is easily overlooked is that "int i;" has different semantics
from "Path p;". In "int i;", i is not initialized at all; in
"Path p;", p _is_ initialized with the default Path constructor. This possibly
confusing point is another reason not to use the pattern unnecessarily.
</rant>
- Johan
Can you check please.
+ if(Geom::are_near(dot(v1,v2),1.0)){ // P1 is within a straight line
I would use cross here, which is more numerically stable in this case
because it has error that is linear rather than quadratic with
divergences (I think).
+ if(Geom::are_near(cross(v1,v2),0.0)){ // P1 is within a straight line
Can you fix the spacing up to match the code - you've go a somewhat
arbitrary mix of no space, single space and double space around
operators.
Other than that, it looks fine.
njh
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