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Clipping

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Could anyone point me to a tutorial about how to set up the DirectDraw clipper? I have some code, but it doesn't work. At all. What so ever. :) When I try it, the first image blt works, but from then on, the blts fail, so I assume that my clipper set up is whacked. Cheers SIgma | | | \ / posted in the wrong form: [edit] whoops: Posted this in Game programming, not DX. Damn. Ok, I'll post over there, but don't freak for a double post ok! :)

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LPDIRECTDRAWCLIPPER lpClipper=NULL;//DirectDrawClipper

result = lpDD->SetDisplayMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_DEPTH, 0, 0);
result = lpDD->CreateSurface( &ddsd, &lpFront, NULL );
result = lpDD->CreateSurface(&ddsd, &lpBack, NULL);

// Create a clipper (used in IDirectDrawSurface::Blt call)
result = lpDD->CreateClipper(0, &lpClipper, NULL);
if( result!=DD_OK )
{
return false;
}

result = lpClipper->SetHWnd(0, g_hWindow); //Client area of the window
if( result!=DD_OK )
{
return false;
}

result = lpBack->SetClipper(lpClipper);
if( result!=DD_OK )
{
return false;
}




NOTE: Don't try BltFast() with clipper - only Blt() or Flip()

PS: That's quick cut out of the working app - hope it helps

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Well, i got my code to work. I was attaching the clipper BEFORE I initialized the surface! Oopps...

You seem to be doing the attaching in WAY less code than me tho....I'll try your method. thx man

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Actually it doesn't work 100% If I move off the screen at a diagonal angle, it crashes. Any idea what could cause this?

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first question: is it fullscreen app or windowed?
second question: do you attach clipper to front surface or to the back one?

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You'd better post some code of yours, where are
- Clipper creation and attachment
- Blitting/Flipping Back to Front surfaces
- Viewport movement

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clipping creation


LPDIRECTDRAWCLIPPER MercuryEngine::DDCrClipper(LPDIRECTDRAWSURFACE7 lpdds,
int num_rects,
LPRECT clip_list)
{
int index; //loop var
LPDIRECTDRAWCLIPPER DDclipper; // our clipper
LPRGNDATA region_data; //contains clip list

if(FAILED(lpdd->CreateClipper(0,&DDclipper,NULL)))
return(NULL);

//creat clip list from data sent
region_data = (LPRGNDATA)malloc((sizeof(RGNDATAHEADER) + num_rects * sizeof(RECT)));

//copy rects into region data
memcpy(region_data->Buffer, clip_list , sizeof(RECT)*num_rects);

//set up fields
region_data->rdh.dwSize = sizeof(RGNDATAHEADER);
region_data->rdh.iType = RDH_RECTANGLES;
region_data->rdh.nCount = num_rects;
region_data->rdh.nRgnSize = num_rects * sizeof(RECT);

region_data->rdh.rcBound.left = 64000;
region_data->rdh.rcBound.top = 64000;
region_data->rdh.rcBound.right = -64000;
region_data->rdh.rcBound.bottom = -64000;

//find bounds for clipping
for(index = 0; index < num_rects; ++index)
{
//test if the next rectangle union with the current bound is alrger
if (clip_list[index].left < region_data->rdh.rcBound.left)
region_data->rdh.rcBound.left = clip_list[index].left;

if (clip_list[index].right < region_data->rdh.rcBound.right)
region_data->rdh.rcBound.right = clip_list[index].right;

if (clip_list[index].top < region_data->rdh.rcBound.top)
region_data->rdh.rcBound.top = clip_list[index].top;

if (clip_list[index].bottom < region_data->rdh.rcBound.bottom)
region_data->rdh.rcBound.bottom = clip_list[index].bottom;

}

//now we have computedthe bounding rectangle region and set up the data
//now we deal with the clipping list

if(FAILED(DDclipper->SetClipList(region_data,0)));
{
delete(region_data);
//return(NULL);
}

if(FAILED(lpdds->SetClipper(DDclipper)));
{
delete(region_data);
//return(NULL);
}

//and now we are done
delete(region_data);
return(DDclipper);
}



Attach then Blt source

RECT clipper_rect[1] = {0,0,799,599}; //fullscreen clipping area
...
//attach a clipper to the backsurface
DDclipper = GameEngine.DDCrClipper(DDback,1,clipper_rect);

BLT HERE

//draw the back ground image
if(FAILED(DDback->Blt(&dest_rect,DDback_sprite,&src_rect,DDBLT_WAIT, NULL)))
{
Application->MessageBoxA("Error","Boom",MB_OK);
Application->Terminate();
}


//draw the BOB sprite
if(FAILED(DDback->Blt(&bob.dest_rect,bob.DDBOB,&bob.src_rect ,(DDBLT_WAIT | DDBLT_KEYSRC),NULL)))
{
//nail any errors that get through
hr = DDback->Blt(&bob.dest_rect,bob.DDBOB,&bob.src_rect ,DDBLT_WAIT,NULL);
//display said error
Application->MessageBoxA(buf,"Boom",MB_OK);
Application->Terminate();
}

//flip
while(FAILED(DDprimary->Flip(NULL,DDFLIP_WAIT)));



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I had once tried to use windows regions with clipper, but that failed, too (strange, perhaps it's a windows bug), so I've clipped to hWnd and Back surface and

lpClipper->SetHWnd(0, g_hWindow);
lpBack->SetClipper(lpClipper);

works fine for me in fullscreen and windowed modes

EDIT: Damn that tags!

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