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Animating tiles in 2D


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#1 rocklobster   Members   -  Reputation: 415

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Posted 27 January 2013 - 10:54 AM

Hey guys,

 

I'm working on a little 2D framework (I usually do 3D stuff so I'm not too sure how some things should be handled in 2D). My question is how to handle animation of tiles (eg. Water) which are stored in a vertex buffer with the rest of the grass (terrain) tiles. Basically I have a map which can be represented like so in a text file:

 

1 1 1 1 

1 1 2 1 

1 1 2 1

1 1 1 1

 

Each number represents a different type of tile, and a tile is basically a texture coordinate (bottom left) for the location of the tile in the texture atlas and a number representing the size of a tile (eg 1.0f / 16.0f, because my atlas is 2048x2048 and I have 16 tiles in a row).

 

struct Tile
{
    float m_tileSize;
    glm::vec2 m_texCoord;
};

 

My vertex buffer is constructed by iterating through two for loops (one for width and height of map) and constructing the vertices for each quad, and using the texture coordinates of the corresponding tile in that position.

 

I want to expand my tile class so it can contain animation information, and because i'm using a texture atlas (and not drawing each tile separately) I cant just swap the texture for animation, I must update the texture coords. I'm not sure if it is a good idea to update this VBO each frame, to modify texture coordinates for animated tiles. This sounds like premature optimisation to me, even if so, i'd like some advice on how other people handle animation like this?

 

Thanks guys



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#2 Waterlimon   Crossbones+   -  Reputation: 2516

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Posted 27 January 2013 - 11:23 AM

1) You can update the texture itself. I believe minecraft did something like this. This has the possibly not wanted effect of animating all the tiles using that texture in the same way. And updating the texture isnt probably very cheap either.

2) In the shader add some offset to the texture if the tile is animated based on the amount of tile passed and amount of keyframes the tile animation has. So each vertex will have some isAnimated style property (0 to keyframecount) and when you render all the tiles you pass "Time" in. And then the shader adds to each texcoord something like floor(time%keyframecount) units. In the tile sheet you need to make animated tiles be next to each other in some specific direction (so its a line). For unanimated tiles just have isAnimated be 0 (isAnimated would be a per vertex vertex attribute)
You could also add another vertex attribute (or make isAnimated have 2 components) to set the animation speed of that specific tile

3)Update the texcoords using glBufferSubData each time you want the animation to change. I believe this is the most flexible, allowing each tile to animate in its own pace, but the cost might be higher than 2

edit:

Edited by Waterlimon, 27 January 2013 - 11:27 AM.

o3o


#3 rocklobster   Members   -  Reputation: 415

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Posted 27 January 2013 - 11:27 AM

Thanks for the reply,

 

So with number 2, this would require me to have a separate draw call for animated tiles though yeah? Other than that, that sounds like a good option. However I would have to change some stuff around.



#4 Waterlimon   Crossbones+   -  Reputation: 2516

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Posted 27 January 2013 - 11:31 AM

It doesnt require it.

Basically now you have for each vertex:
-Position
-Tex coord

and you need to add
-Animation (2 float components?)
*first component is amount of frames the animation has
*second component is speed of animation

For nonanimated tiles animation is 0,0

When drawing all the tiles, you pass a "Time" uniform to the shader.

In the shader, you add to the tex coords
texCoord.x=texCoord.x + float(((time*animationSpeed)%keyframes))*widthOfTileTexture

so normal tiles are normal. But animated tiles take 1 texture from a row of textures of specified size (in the same tile sheet as normal tiles) depending on time

edit:

so basically to get a tile animated, in your tile sheet you place the animation sequence of the tile on a horizontal row. then in the vertex attribute (the animation one) you set how many tiles long the sequence is, and how fast it should play.

Edited by Waterlimon, 27 January 2013 - 11:38 AM.

o3o


#5 rocklobster   Members   -  Reputation: 415

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Posted 27 January 2013 - 11:54 AM

Ah cool, thanks i'll do that! Shaders ftw as usual. 






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