added some info

Author: megai2

README.md

@@ -1,6 +1,53 @@
 # d3d9_wrapper
 
+[![Build status](https://ci.appveyor.com/api/projects/status/4dxo5hw1sq6p67lx?svg=true)](https://ci.appveyor.com/project/megai2/d3d9-wrapper)
+
 Wrapper for d3d9 API that includes hooking and custom d3d9 loading
 
+## How API functions are hooked?
+
+API functions is wrapped around with event triggers this way:
+
+```
+wrapped_API_function(params) {
+  trigger_event(API_function_pre, params);
+  ret = API_function(params)
+  trigger_event(API_function_post, params, ret);
+}
+```
+
+Currently only IDirect3D9 and IDirect3DDevice9 calls are wrapped.
+
+## How to work with this?
+
+Here is quick sample on how to draw something before Present call
+
+```
+#include "gw2al_d3d9_wrapper.h"
+#include "gw2al_api.h"
+
+gw2al_api_ret gw2addon_load(gw2al_core_vtable* core_api)
+{
+  //get loader api
+	gw2al_core_vtable* gAPI = core_api;
+
+  //get d3d9 wrapper enable_event function
+	D3D9_wrapper d3d9_wrap;
+	d3d9_wrap.enable_event = (pD3D9_wrapper_enable_event)gAPI->query_function(gAPI->hash_name((wchar_t*)D3D9_WRAPPER_ENABLE_EVENT_FNAME));  
+  
+  //enable IDirect3DDevice9::Present pre API-call event
+  d3d9_wrap.enable_event(METH_DEV_Present, WRAP_CB_PRE);
+  
+  //watch for this event with OnDevPrePresent callback
+  D3D9_WRAPPER_WATCH_EVENT(L"change_me", L"D3D9_PRE_DEV_Present", DrawSomethingBeforePresent, 0);    
+}
+
+void DrawSomethingBeforePresent(D3D9_wrapper_event_data* evd)
+{
+  //evd contains pointers to API return data and original call stack pointer
+  //TODO: draw something
+}
+
+```
 
-Look include/gw2al_d3d9_wrapper.h for details for now.
+Look include/gw2al_d3d9_wrapper.h for details.