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AppGameKit Classic Chat / How to NOT clear backbuffer on mobile devices?

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Clonkex
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Posted: 10th May 2014 17:49
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Hi all,

I'm making an app that requires a "blending" effect. Actually more like trails behind every object that moves. On PC, EnableClearColor(0) works a treat to keep the backbuffer uncleared, and I just use a fullscreen transparent black sprite to fade out the previously rendered sprites. The problem is, I can't make this work on my phone (Samsung Galaxy S3). I did some research, and as far as I can tell, the backbuffer is forcibly cleared on some devices (but it works on my Nexus 7).

My question is this: Is there a way around this? If not, can anyone suggest an alternate solution? Preferably as fast as possible as my app is pretty performance-heavy as it is.

I'd appreciate any help you can give, because this may completely sutff weeks/months of work if I can't figure out a solution


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Markus
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Posted: 10th May 2014 17:54
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my experience with EnableClearColor is , do not touch.

AGK 108 (B)19 : Windows 8.1 Pro 64 Bit : AMD Radeon HD 6670
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Clonkex
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Posted: 10th May 2014 18:04
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Quote: "my experience with EnableClearColor is , do not touch."


Mmm, I get that feeling. The only problem is that I have no idea what else to do...


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xCept
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Posted: 10th May 2014 19:10
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EnableClearColor doesn't work on most devices and causes incredibly unpredictable results. V2 supports render-to-image features, which could be used to achieve some effect. However, I have had no luck getting that feature to work on anything but Windows yet despite Paul stating in the change log they should work on all devices.
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Markus
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Posted: 10th May 2014 20:22 Edited at: 12th May 2014 14:03
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hmm, maybe try v2 alpha,
i believe the new sprite blendmodes or render to image are ready.

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Clonkex
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Posted: 11th May 2014 04:07
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Quote: "EnableClearColor doesn't work on most devices and causes incredibly unpredictable results."


Yeah...

Quote: "hmm, maybe try v2 alpha,
i believe the new sprite blendmodes or render to image are ready."


I can't really. My app is complete except for this one nasty bug, and I assume most of V2 is not actually working yet. I need a stable platform. Plus, I can't afford V2 even at that price.

NOW what am I going to do...


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Naphier
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Posted: 11th May 2014 07:20
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This is a tough one!
I think I understand what effect you're after, but doing it with making the backbuffer static for a frame doesn't sound like a stable way to go. Can you do a short video on the effect? Maybe I'll be able to better understand what you're after. The only thing I can think of right now is to make clones of your sprites as they move, set the clone transparency to 50%, then delete the clone on the next frame, or leave it alive but always have it move 1 frame slower. It's not a simple thing to do!

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Clonkex
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Posted: 11th May 2014 09:11
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Quote: "This is a tough one!"

Quote: "It's not a simple thing to do!"


Indeed, but it was actually the AGK help files that told me to do it the way I did, and made it seem to simple.

Quote: "Can you do a short video on the effect? Maybe I'll be able to better understand what you're after."


Sure, just give me a while.

Quote: "The only thing I can think of right now is to make clones of your sprites as they move, set the clone transparency to 50%, then delete the clone on the next frame, or leave it alive but always have it move 1 frame slower."


That's one "solution" (it wouldn't look very good) that I already thought of, but the problem is that my app is already pushing performance to the limits and has 1000-5000 sprites on screen. Still, a lot of the performance drain is in the calculations required for the sprites, so I'll do some experiments...


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Digital Awakening
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Posted: 11th May 2014 12:16 Edited at: 11th May 2014 12:18
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Render to image should work in Alpha 3. I have tested it on PC and Ouya. It wasn't difficult to add to RTA once I figured out how it worked. But this means that you will do a full screen redraw and if you are short on fillrate, that could be a problem. You can always render to a smaller image and scale that up, I do that with RTA on Ouya. I use render to image to allow users to shrink the image and adjust for overscan.

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Clonkex
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Posted: 11th May 2014 15:29
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Rendering to a smaller image would be bad because my app relies on crisp graphics (if it feels like I'm being intentionally cryptic about what my app is, it's because I am ).

My current thinking is that I might try to create an image via memblocks and modify it each frame underneath sprite positions. The only problem is that creating a new fullscreen image from a memblock each frame may simply kill performance. I just can't win.

I'm also looking into the possibility of converting all of my code over to Cocos2D-X, because I already have my code running in C++. Unfortunately Cocos doesn't have very clear documentation and it may simply be too difficult. Not sure what I would do then...


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The Zoq2
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Posted: 11th May 2014 16:01
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Quote: "My current thinking is that I might try to create an image via memblocks and modify it each frame underneath sprite positions. The only problem is that creating a new fullscreen image from a memblock each frame may simply kill performance. I just can't win."


I did some experiments with that a while back and it turned out that it is not viable at all. If I recall correctly I was only able to keep it above 60 fps if the image was smaller than 200x200 and that was on a PC. Render to image should be a lot faster and I don't see why you wouldn't be able to render at the real resolution.

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Clonkex
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Posted: 11th May 2014 16:12
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Hmm... Yeah, I now remember that I did some tests a while back relating to realtime landscape modification and it was really slow.

The biggest problem with render-to-texture is that I can't afford V2 yet, and I don't even know what its status is; i.e., does it work reliably for everything V1 can do?


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The Zoq2
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Posted: 11th May 2014 17:17
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I think V2 the current V2 alpha is pretty stable, I was able to complete my nexus competition entry using it and right now im pretty sure that it's fully backwards compatible with V1

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