[cairo] Re-working cairo_current_path

[Owen Taylor]

On Mon, 2005-01-24 at 13:30 -0500, Kristian Høgsberg wrote:
> Keith Packard wrote:
> > Around 11 o'clock on Jan 24, Carl Worth wrote:
> > 
> > 
> >>Keith, what was your proposed data structure for the path? A list of
> >>double with magic values to specify each operator?
> > 
> > 
> > Perhaps:
> > 
> > typedef union {
> > 	struct {
> > 		enum { Move, Draw, Curve } Type;
> > 		uint16_t	len;
> > 	} head;
> > 	double value;
> > } cairo_path_elt_t;
> > 
> > Or is that too complicated?  It seems like a feature to encode the length 
> > of each element right into the element; it might permit the kinds of 
> > elements to be extended in the future (and exposed in some new call) 
> > without completely wrecking all existing code.
> > 
> > But, I'd support the simpler
> > 
> > #define CAIRO_PATH_MOVE		0.0
> > #define CAIRO_PATH_DRAW		1.0
> > #define CAIRO_PATH_CURVE	2.0
> > 
> > if that seems nicer.
> > 
> > (oh, the names above are unconsidered and should be taken only as 
> > representative of the structure of the objects)
> 
> What about:
> 
> struct cairo_path_element {
> 	enum { move, draw, curve } type;
> 	uint16_t length;
> 	union {
> 		struct { double x, y; } move_to;
> 		struct { double x, y; } line_to;
> 		struct { double x1, y1, x2, y2, x3, y3 } curve_to;
> 	};	
> };
>
> possibly with a CAIRO_PATH_ELEMENT_NEXT macro that does the pointer 
> arithmetic to get the next element.

Would an opaque type with an iterator API work? E.g.:
 
 cairo_path_iterator iter;

 for (have_element = cairo_path_iterator_begin (path, &iter);
      have_element;
      have_element = cairo_path_iterator_next (&iter)) {

     switch (cairo_path_iterator_current_element (&iter)) {   
     case CAIRO_PATH_MOVE_TO:
         {
             double x, y;
             cairo_path_iterator_get_move_to (&iter, &x, &y);
             [...]
         }
         break;
     }
 }

Or:

 cairo_path_iterator iter;
 int have_element;

 for (have_element = cairo_path_iterator_begin (path, &iter);
      have_element;
      have_element = cairo_path_iterator_next (&iter)) {

      cairo_path_element_t *element = cairo_path_iterator_current_element (&iter);
      switch (element->type) {
      case CAIRO_PATH_ELEMENT_MOVE_TO:
          /* Do stuff with element->move_to.x element->move_to.y; */
      }
  }

Which I guess is Kristian's proposal, but less reminiscent of the API
disaster that is XInput.

Regards,
						Owen

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