[Gdiplus 11/15] Implement GdipCreateRegionRect

Adam Petaccia adam at tpetaccia.com
Wed Jul 9 09:56:48 CDT 2008

I was just about to reply to your first mail when I found this pop up.

To quote MSDN: 

"The Region class describes an area of the display surface. The area can
be any shape. In other words, the boundary of the area can be a
combination of curved and straight lines. Regions can also be created
from the interiors of rectangles, paths, or a combination of these.
Regions are used in clipping and hit-testing operations."

Because the area can be any shape, including curved lines, I chose
GpPath as the base object. I imagined the data you're talking about
stored in an array of regionOperation structs, or something of the like
- so we still have the ability to do non-rectangular hit-testing and can
now getRegionData. I'll write some more tests to confirm/deny this

On Wed, 2008-07-09 at 15:41 +0100, Huw Davies wrote:
> On Wed, Jul 09, 2008 at 11:58:23AM +0100, Huw Davies wrote:
> > This doesn't look right.  See the GdipGetRegionData tests (and extend
> > them to add paths), these are supposed to help understanding how
> > regions are stored.  It looks to me that a region is stored as a
> > sequence of rects and paths that are combined with various CombineMode
> > ops.
> Hi Adam,
> In fact you want to store the region elements as a binary tree,
> something like this:
> typedef enum element_type
> {
>     rect_element = 0x10000000,
>     path_element,
>     empty_element,
>     infinite_element
> } element_type_t;
> typedef struct region_element
> {
>     DWORD type_or_op; /* One of the CombineModes or element_type_t */
>     union
>     {
>         GpRectF rect;
>         GpPath *path;
>         struct
>         {
>             struct region_element *first;
>             struct region_element *second;
>         } operands;
>     } elem_data;
> } region_element_t;
I had something in mind that resembled this, but without a union. That's
a better idea.

> struct GpRegion
> {
>     region_element_t root;
> };
> A region element is either a rect, path or a combining op (in which
> case it has two children, 'first' and 'second').  The data returned by
> GdipGetRegionData is then basically what happens if you walk the tree,
> favouring the 'first' node at every branch.
I had an idea of something like that.

> Does that make sense?
All of it.
> Huw.

I didn't mean to imply that I ignored the region.c header, but I didn't
use any of its information for the bounds tests yet, so I didn't add
them to the struct (and I've learned to add things as needed).

Thanks for the additional help.
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