Reaching OS3.9 (yes, OS3.9) -compatible offscreen Rastport with private LayerInfo+1Layer to have offscreen clipping

I've been coding raster routines under OS3.2 lately, and at some point in my life I figured out the "graphics.library draw call that asks for a struct RastPort *", would not clip , and so continue to draw anywhere in memory, a privately inited Rastport + bitmap inited with:

struct RastPort mytemprastport;
 InitRastport(&mytemprastport);
 mytemprastport.BitMap = thatbm;
 somedrawcall(&mytemprastport); // <- that , will clip no border., mytemprastport.Layer is NULL 

.... super usefull if you actually draw a rectangle with same size, and know that you don't need clipping anyway. Great. But clipping, need I. At some other poijnt of my tumulturous life I found this usefull piece of code (somewhere), that allows to have a complete Offscreen, unrelated to any screen or anything, and that does a legitimate clippable Layer+rastport to your bitmap:

void OffscreenBitMap_Init(OffscreenBitMap *ofsbm, 
		int pixelWidth, int pixelHeight , 
		int depth,
		int bmFlags,
		struct BitMap *friendBitmapForMode)
{
	
	if(!ofsbm) return;
    ofsbm->_layer = NULL;
    ofsbm->_layerinfo = NULL;
    ofsbm->_rp = NULL;
    ofsbm->_bm = NULL;
	// the way to create RastPort that actually clips drawing.
	if(friendBitmapForMode) depth = friendBitmapForMode->Depth;
	ofsbm->_bm = AllocBitMap(pixelWidth,pixelHeight,depth,bmFlags, friendBitmapForMode);
	if(!ofsbm->_bm) return;

	ofsbm->_layerinfo = NewLayerInfo();
	if(!ofsbm->_layerinfo) {  OffscreenBitMap_Close(ofsbm); return; }

	ofsbm->_layer = CreateUpfrontLayer(ofsbm->_layerinfo, ofsbm->_bm, 0, 0, pixelWidth - 1, pixelHeight - 1, 0, NULL);

	if(!ofsbm->_layer) {  OffscreenBitMap_Close(ofsbm); return; }
	ofsbm->_rp = ofsbm->_layer->rp;
	
}
void OffscreenBitMap_Close(OffscreenBitMap *ofsbm)
{
    if(ofsbm->_layer) DeleteLayer (0,ofsbm->_layer);
    ofsbm->_layer = NULL;
    if(ofsbm->_layerinfo) DisposeLayerInfo(ofsbm->_layerinfo);
    ofsbm->_layerinfo = NULL;
    ofsbm->_rp = NULL;
    if(ofsbm->_bm) FreeBitMap(ofsbm->_bm);
    ofsbm->_bm = NULL;	
}

... works great no OS3.2, problem is, on OS3.9 , as soon you use NewLayerInfo() and CreateUpfrontLayer(), it ends up trashing the whole intuition at some point. No idea why, I 've heard layers.library has a long history, but well i'm "that close" to achieve OS3.9 compatibility. An idea to make that code "safe for OS3.9" ? Is there a more "soft way" to create a private clipable rastport ? Am I supposed to use LockLayerInfo()/Unlock() ? Any tips ?