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Testing our changes Well now that we've covered our approach to switching the graphics pipeline state, as well as playing around with our buffer comparison routines, let's do some flexin' and use some of this knowledge in our code! We're not going to do anything that radical today. I'm simply going to demonstrate some of what we've covered in today's tutorial. Obviously it's pretty bare bones, but the power is there to handle more advanced tasks for your scene. Step One In our createProgram method we just need to add/update the following code: //load up a TGA image hr = pInterface->getTextureInterface()-> addTexture("data\\textures\\title.tga", TITLE); if(FAILED(hr)){ return E_FAIL; } pInterface->setState( ZBUFFER, DISABLE );//disable our depth buffer pInterface->setState( LIGHTING, DISABLE );//disable our lighting //enable our blending calculations pInterface->setState( ALPHABLENDING, ENABLE ); //set our source parameter to the alpha information of the source pixel pInterface->setState( SRC_BLEND, SRC_ALPHA ); //set our destination parameter to 1-alpha information of the source pixel pInterface->setState( DEST_BLEND, INV_SRC_ALPHA ); That's pretty much all we need to do! When we run our example along with the updated interface DLL's, we'll see the following (with our OpenGL DLL): References TGA Loader code from theTutor at GameTutorials.com. OpenGL Game Programming by Hawkins/Astle. Page 217-219 Conclusion Well there you have it. We did a lot of work today on our engine, and learned a bit about manipulating the state information of the graphics pipeline, as well as being able to update/modify the existing underlying renderer interface codebase without having to touch and/or recompile our application. Again, note that this approach to our state machine within the graphics pipeline is merely one way to do things. Another possible approach, is to use the use of bit fields to represent our state(s), which was fleshed out somewhat by gamedev.net reviewer RusselB. #define ES_LIGHTING 1 // or 0x0001 #define ES_ZBUFFER 2 // or 0x0002 #define ES_ALPHABLENDING 4 // or 0x0004 #define ES_SRC_BLEND 8 // or 0x0008 #define ES_DEST_BLEND 16 // or 0x0010 #define ES_ALPHATEST 32 // or 0x0020 Which can then be used in combination with each other to allow the engine to accept method calls such as: setState( ES_LIGHTING | ES_ZBUFFER ); //set our state disableState( ES_LIGHTING | ES_ZBUFFER ); //disable our state Any comments, questions or concerns can be sent to Wazoo AT WazooEnterprises death-to-spam DOT com.

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