DrawSetTextureRGBA

void DrawSetTextureRGBA(int id, const unsigned char *rgba, int wide, int tall, int hardwareFilter, bool forceReload)

This is a function that you should use to draw raw RGBA data to the HUD, for example when you are rendering a mask. DrawSetTextureRGBA is one of the worst documented features in the SDK, and hasn't been seen working in any way. The following code is by the book, but doesn't work at all (it just paints a white fog over the screen).

	//abPic is an unsigned char[128][128] with some texture data
	m_iHudTexture=surface()->CreateNewTextureID();
	surface()->DrawSetTextureRGBA(m_iHudTexture,(unsigned char*)abPic,128,128,false,true);
	Assert(surface()->IsTextureIDValid(m_iHudTexture));
	surface()->DrawSetColor(Color(255,255,255,128));
	surface()->DrawTexturedRect(0,0,GetWide(),GetTall());

Emails on HLCoders (March 2005, [hlcoders] DrawSetTextureRGBA) about this issue haven't helped a bit. We, as the Source modding community can only hope Valve will eventually fix this, or give information on how this function should be used.