LBitmapRgn::GetClipSegments

#include "ltwrappr.h"

virtual L_INT LBitmapRgn::GetClipSegments(nRow, pSegmentBuffer, puSegmentCount)

L_INT nRow;	/* number of the row */
L_UINT * pSegmentBuffer;	/* pointer to a buffer */
L_UINT * puSegmentCount;	/* pointer to a variable to be updated */

Gets the segments contained in the region for a particular row.

Parameter	Description
nRow	The number of the row for which to get the segments. The first row is 0, and the last row is 1 less than the height of the class object's associated bitmap.
pSegmentBuffer	Pointer to the buffer to be updated with the segments from row nRow contained in the region. This buffer should be large enough to contain twice as many values as indicated in *puSegmentCount.
puSegmentCount	Address of a variable to be updated with the number of filled values in the pSegmentBuffer.

Returns

SUCCESS	The function was successful.
< 1	An error occurred. Refer to Return Codes.

Comments

To use this function, first call LBitmapRgn::SetRgnXForm with pXform set to NULL, and then use LBitmapRgn::GetRgnBounds to get the boundaries of the class object’s associated bitmap. The bounding rectangle will indicate which rows are contained in the region. Go through all the rows contained in the region to get the segments contained in the region.

The segments are returned as an array of pairs of horizontal offsets. The first point in the pair is the beginning of the segment (it is contained in the region). The last point in the pair is the end of the segment. To follow the Windows rules, the end of the segment is the first point NOT CONTAINED in the region.

In most regions, there will be one segment per row. However, some regions can have 0, 1, 2 or more segments.

For example, assume that for a particular row there are two segments. pSegmentBuffer will be filled with 4 values and puSegmentCount will be filled with the value 4. Let’s call them x0, x1, x2, x3. In this case:

$image\sqrblit.gif$ portion from 0 to x0 – 1 is OUTSIDE the region

$image\sqrblit.gif$ portion from x0 to x1 - 1 is INSIDE the region

$image\sqrblit.gif$ portion from x1 to x2 – 1 is OUTSIDE the region

$image\sqrblit.gif$ portion from x2 to x3 – 1 is INSIDE the region

$image\sqrblit.gif$ portion from x3 to pBitmap->Width – 1 is OUTSIDE the region

It is recommended that you allocate a buffer large enough to hold all the possible segments. To get the maximum number of segments, call LBitmapRgn::GetClipSegmentsMax. Allocate an array of unsigned values that can contain the largest number of segments. See the example for more details.

Required DLLs and Libraries

LTDIS

For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application.

See Also

Functions:	LBitmapRgn::GetClipSegmentsMax, LBitmapRgn::GetRgnBounds, LBitmapRgn::SetRgnXForm, Class Members
Topics:	Raster Image Functions: Creating and Using a Region
	Working with the Existing Bitmap Region

Example

The following example sets the pixels of the first row inside a region to black.

L_VOID ClearFirstRow(LBitmapBase & Bitmap, L_TCHAR * pszFile)
{
   LBitmapRgn Region;
   L_UINT uSegments;
   L_UINT * pSegments;
   RECT rcRegion, rcClip;

   Bitmap.Load(pszFile);
   Region.SetBitmap(&Bitmap);
   SetRect(&rcRegion,
           Bitmap.GetWidth() / 4,
           Bitmap.GetHeight() / 4,
           3 * Bitmap.GetWidth() / 4,
           3 * Bitmap.GetHeight() / 4);

   Region.SetRgnRect(&rcRegion);

   // Get the maximum number of elements in a row, so we
   // know how big the array of segments should be.
   Region.GetClipSegmentsMax(&uSegments);

   // Allocate an array large enough to store the maximum
   // number of segments. Note that LBitmapRgn::GetClipSegmentsMax
   // took into account that each segment has two extremities.
   pSegments = (L_UINT *) GlobalAllocPtr(GMEM_MOVEABLE,
                                         uSegments * sizeof(L_UINT));

   if(!pSegments)
      return; // Not enough memory!

   // Get the region bounds, so we know the first row
   Region.SetRgnXForm(NULL);
   Region.GetRgnBounds(&rcClip);

   // Get the segments for the first row
   Region.GetClipSegments(rcClip.top, pSegments, &uSegments);

   // Do something with the segments:
   // To keep this example simple, we will set
   // the pixels in the segments to 0.
   for (L_UINT i = 0; i < uSegments; i+=2)
      for (L_UINT j = pSegments[i]; j < pSegments[i + 1]; j++)
          Bitmap.PutPixelColor(rcClip.top, j, 0);

   // Free the segments array
   GlobalFreePtr(pSegments);
}