iTorque 2D engine efficiency boost

Hello everyone.

-- note, this is more a story just below, if you are just here to get the performance boost,
scroll all the way to the bottom and find the code (it's simple I promise). otherwise enjoy the story :)


--------------- STORY ---------------


I just recently finished work on a game for the iPad called Space Fart (you can find a blog about it on GarageGames here -> Blinker Studios - Space Fart)

I began this project by running a simple test project on an iPad (1st Generation) and I printed out the frame rate to see how well it did.
I was mortified when I saw that with ONLY a background of 1024 x 1024 pixels it ran at (I forget now, and don't have the iPad with me to reproduce) about 30 - 35 fps. That was ONLY A BACKGROUND!!! Obviously when we added ANYTHING else to the scene the FPS dropped even further until our game was sporting a nice 15 - 20 fps. This was just simply not acceptable.

So what I did was run some profiling tools that I have on my Mac and one of them is called Open GL ES Performance Detective (pretty awesome name) and what it does is: it tells me the FPS of a running app on a device that is using OpenGL ES (which iTorque does use) and when it drops to a level that I find unacceptable I click the Collect Evidence button and it immediately starts checking the app to see what is going on and tells me the problem.

When I ran the tool on Space Fart for the iPad, this is what it told me:


As you can see, it is saying that the FPS is limited by the graphics pipeline, and it offers some suggestions such as reducing the amount of pixels pushed to the screen and so forth. BUT the most notable is the one at the bottom where it says that the app is using alpha tests. I thought that this was normal because obviously you need to take out the alpha pixels in an image that uses alpha or else you get a big white spot wherever the alpha pixels were.

well after this I did some research on OpenGL ES for IOS devices and I came across this page -> Open GL ES Tuning .

If you read through that page it offers a lot of tweaks that will improve the graphics performance of an app, but at the very bottom of the page it mentions that you need to avoid Alpha testing using GL_ALPHA_TEST. I took a look through the engine and sure enough, I found it. Now I thought that commenting out GL_ALPHA_TEST would make white pixels appear on every image that I drew that had alpha enabled, but I soon found out that Blending is the fix for that. If you turn off blending AND comment out GL_ALPHA_TEST the white pixels will appear, but if you turn on Blending and leave out Alpha test, the alpha pixels are blended with actual coloured pixels and the result is as if the alpha pixels were ignored.

This is good news because on every iTorque game, blending is on by default for every scene object. So if you have a background of any type, and blending is enabled on it, you do not need to do an alpha test.

So I went and commented out the glEnable(GL_ALPHA_TEST) and glAlphaFunc(.....) and ran my projects again to find that Space Fart, which had a measly 23 FPS, now had a decent 45 - 50 fps. As well the test project with just the background went from 30 - 35 FPS to a solid 60 FPS.

Incredible, its like a 300% speed boost with no catch. At least I believe there is no catch (I would appreciate any comments below, tell me if there is any trouble). The reason apparently is that GL_ALPHA_TEST disables hardware optimizations for the fragment shader.

So I think that EVERYONE that is using iTorque needs to read this code fix, because I also saw a performance boost on the iPhone 3G AND the iPhone 4. (I am also 100% convinced that this fix will allow for at LEAST 30 up to 40 fps using Retina Display, a good tutorial to get that going found here -> Retina Display by Pedro Vicente , seeing as the iPad 1 and iPhone 4 have the exact same CPU and the iPad has a higher resolution.)

So thank you for following along, it was a long story I know, but treat yourself to the code down below. it seems like its a small amount of code but enjoy anyways :)



--------------- Story End, Time for the Code ----------------

comment out lines 2918 and 2919 inside of "iTorque2D1_5_Preview2/engine/source/T2D/t2dSceneWindow.cc". (change iTorque2D1_5_Preview2 to whatever version you are currently using.

this is what it should look like before and after:


before:

// Setup new viewport.
    dglSetViewport(updateRect);
 	
    // Set ModelView.
    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();
    glLoadIdentity();

    // Enable Alpha Test.
    glEnable        ( GL_ALPHA_TEST );      //<------------------------------- you want to comment out this line
    glAlphaFunc     ( GL_GREATER, 0.0f );//<------------------------------- and this line
    
    glDisable       ( GL_DEPTH_TEST );
    //glEnable      ( GL_DEPTH_TEST );
    //glDepthFunc       ( GL_LEQUAL );

	// implement "Don't Render Object" functionality.  Hide it before we render, unhide it afterwards.
	bool previousDontRenderObjectVisibility = false;
	if ((mpDontRenderObject != NULL) && mpDontRenderObject->mVisible)
	{
		previousDontRenderObjectVisibility = true;
		mpDontRenderObject->mVisible = false;
	}

and After

// Setup new viewport.
    dglSetViewport(updateRect);
 	
    // Set ModelView.
    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();
    glLoadIdentity();

    // Enable Alpha Test.
        //glEnable        ( GL_ALPHA_TEST );      <-------------------------- Commented out
        //glAlphaFunc     ( GL_GREATER, 0.0f );<-------------------------- Commented out
    
    glDisable       ( GL_DEPTH_TEST );
    //glEnable      ( GL_DEPTH_TEST );
    //glDepthFunc       ( GL_LEQUAL );

	// implement "Don't Render Object" functionality.  Hide it before we render, unhide it afterwards.
	bool previousDontRenderObjectVisibility = false;
	if ((mpDontRenderObject != NULL) && mpDontRenderObject->mVisible)
	{
		previousDontRenderObjectVisibility = true;
		mpDontRenderObject->mVisible = false;
	}

Thanks again and keep an eye out for any more apps from Blinker Studios ;)