A strange problem with regions

Hi!

I'm trying to loop through pixels of a bitmap, check for their RGB values and add to a region if they match with a specified color.

Code:

	for(WORD y=0; y<wBmpHeight; y++)
	{
		for(WORD x=0; x<wBmpWidth; x++)
		{
			for(std::map<char*, CMould>::iterator it=moulds.begin(); it!=moulds.end(); it++) //this map holds 26 different color values and region handles
			{
				if(RGB(pPixels[p+2], pPixels[p+1], pPixels[p]) == it->second.trnsphRGB)
				{ //if the colors match
					int iRes = CombineRgn(it->second.regionHandle, 
                                                            it->second.regionHandle, 
                                                            CreateRectRgn(x, y, x+1, y+1), RGN_XOR); //add this pixel to the region
				}
			}
			p+=3;
		}
		itoa(y, pOut, 10); //just to display the current y line
		SetWindowText(hwnd, pOut);
	}

All goes well and CombineRgn returns COMPLEXREGION (success) until line 138, pixel 514. The function returns ERROR on this and further pixels. I found out with GetLastError() that the error code is 6 (invalid handle). I don't get why it->second.regionHandle is invalid, because the debugger shows the exact same handle address for both- successful and unsuccessful calls to CombineRgn.

The CMould class is nothing special, regionHandle is initialized in the constructor.

Header:

Code:

#ifndef MOULD_H
#define MOULD_H

class CMould
{
public:
	CMould(COLORREF color, char** shouts);
	CMould(){}
	HRGN regionHandle;
	COLORREF trnsphRGB;
	char** pShouts;
};

#endif

CPP:

Code:

#include "stdafx.h"

CMould::CMould(COLORREF color, char** shouts)
{
	trnsphRGB=color;
	memcpy(pShouts, shouts, sizeof shouts);
	regionHandle = CreateRectRgn(0, 0, 1, 1);
}

I can't think of what might be causing it.
Thanks for any help.

I suspect you are just creating a region too complicated for Windows to deal with.

Regions are a screwy thing in the API, my friend. They are actually a very resource consuming object. Thus memory leaking is always lurking around the corner.

Rasterization is a good way around this (in my experience). Instead of adding each pixel to your region at once, add code that does something like:

Example:

Code:

// Sorry for not being up on my MFC... but you should be able to MFC-ify this.
RECT line = {0,0,0,0};
bool inside = false

for(int y = 0; y < wBmpHeight; ++y)
{
    line.top = y;
    line.bottom = y+1;

    for(int x = 0; x < wBmpWidth; ++x)
    {
        // I am switching more to pseudo-coding now, but you get the idea :)
        if(RGB(pixel(y*wBmpWidth+x)) == myTransparentColor)
        {
            if(!inside)
              line.left = x;
        } else
        {
            if(inside)
            {
               line.right = x-1;   // This makes it go back to the last pixel which was good.
               inside = false;

               HRGN extra = CreateRectRgnIndirect(&line);
               CombineRgn(second, second, extra, RGN_XOR);
               DeleteObject(extra); // this is actually probably what killed your code, btw.
            }
        }
    }
   
    // Make sure to finish a line too
    if(inside)
    {
        line.right = x-1;   // This makes it go back to the last pixel which was good.
        inside = false;

        HRGN extra = CreateRectRgnIndirect(&line);
        CombineRgn(second, second, extra, RGN_XOR);
        DeleteObject(extra); // again, we don't want memory leaks.
    }
}

Originally Posted by brewbuck

I suspect you are just creating a region too complicated for Windows to deal with.

hahaha! You are officially my favorite member.

Originally Posted by master5001

Code:

 DeleteObject(extra); // this is actually probably what killed your code, btw.

You are MY favorite member now Thanks, it works flawlessly now, hadn't thought about deleting GDI objects before posting.

Thanks again!

No problemo. I have run into issues like that before and they are so painfully difficult to debug.