A opengl texture transparent hack

  alpha, c++, opengl, textures, transparent

I wish to make an opengl universal texture transparent hack for the DxWnd tool (an open-source program hosted o SourceForge). The hack should work for every program using opengl to render RGBA textures. DxWnd cah hook and redirect all calls from libraries, including opengl32.dll.
I’ve read and tried to implement all suggestions about making a texture transparent, including enabling GL_BLEND, disabling GL_CULL_FACE and setting glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA). In addition, there’s a routine that enforces the alpha bits of all texture pixels.
I expected that, once finished, the result should be a semi-transparent scene, but that doesn’t happen.
For instance, the following is a 3d scene from gl hexen II:
enter image description here
and this is the final result, with some textures not transparent and most pixel colors lost:
enter image description here
Just to demonstrate that DxWnd is able to manipulate color pixels (so that this should not be the cause of the problem) this is the same scene with a filter that recolors every texture:
enter image description here
What could be the reason of the problem? How should I fix it? Please, be aware that since DxWnd is hooking a generic program, it may easily have to confront with opengl calls that have an opposite purpose!

Source: Windows Questions C++