optimization - Effecient tilemap rendering

I have done mostly tile based games, but never really bothered with optimization. I always just rendered all the tiles that convered the viewport. I am currently working on platformer for a mobile device, which has some performance issues, ecspecially when using multiple layers of tiles.

Most tiles are pretty static without animations. I wouldn't really have to render them each frame. The clear() -> draw() loop is really printed into my brain, I'm having a hard time thinking how the handle rendering without clearing the screen each frame.

I'm currently doing this: - start game, render screen once - Once a tile changes, save this in a "tile_changed" array - Each frame, re-render all the changed tiles and clear the array

This works pretty fine, and there is a notable boos in performance. However, there are a view issues - The PlayN framework offers no way to "erase" drawn items. Whenever I want to erase a single tile I have to completely clear the screen and redraw every tile. (PlayN SurfaceLayer). I'm using a scroll background, so can't just fill an empty tile with the background color. I can imagine low level libraries like opengl having this same issue, do they use some sort of workaround for this?

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  I'm not sure how to recognize when new tiles come into the screen whenever the camera moves. I would normally just render the tiles in view each frame, so this never posed a problem.

  
  



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  I have no idea if having such a big drawn rendertarget in memory is a good idea. The player could have walked across a huge map and have thousands of tiles drawn. Should I worry about this?

  
  

Any other optimiztions that I'm missing are appreciated.

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The awnsers note that most engines draw all tiles every frame. But I know that on some less powerfull platforms this is not the case. I believe flashpunk is using some sort of buffer that only draws new tiles when you make changes in the grid. Unfortunately this is not possible for me because I have no way of clearing a single tile without clearing the entire buffer.

I'm looking into optimazations like this, which enable me to have a very large amount of tiles on the screen.