What are the pros and cons of a sprite sheet compa

问题:

I come from a 2D animation background and so when ever I us an animated sequence I prefer to use a sequence of images. To me this makes a lot of sense because you can easily export the image sequence from your compositing/editing software and easily define the aspect.

I am new to game development and am curious about the use of a sprite sheet. What are the advantages and disadvantages. Is file size an issue? - to me it would seem that a bunch of small images would be the same as one massive one. Also, defining each individual area of the sprites seems time cumbersome.

Basically, I dont get why you would use a sprite sheet - please enlighten me.

Thanks

回答1:

Performance is better for sprite sheets because you have all your data contained in a single texture. Lets say you have 1000 sprites playing the same animation from a sprite sheet. The process for drawing would go something like.

Set the sprite sheet texture.
Adjust UV's to show single frame of animation.
Draw sprite 0
Adjust UV's
Draw sprite 1
.
.
.
Adjust UV's
Draw sprite 998
Adjust UV's
Draw sprite 999

Using a texture sequence could result in a worst case of:

Set the animation texture.
Draw sprite 0
Set the new animation texture.
Draw sprite 1
.
.
.
Set the new animation texture.
Draw sprite 998
Set the new animation texture.
Draw sprite 999

Gah! Before drawing every sprite you would have to set the render state to use a different texture and this is much slower than adjusting a couple of UV's.

回答2:

Many (most?) graphics cards require power-of-two, square dimensions for images. So for example 128x128, 512x512, etc. Many/most sprites, however, are not such dimensions. You then have two options:

• Round the sprite image up to the nearest power-of-two square. A 16x32 sprite becomes twice as large with transparent pixel padding to 32x32. (this is very wasteful)
• Pack multiple sprites into one image. Rather than padding with transparency, why not pad with other images? Pack in those images as efficiently as possible! Then just render segments of the image, which is totally valid.

Obviously the second choice is much better, with less wasted space. So if you must pack several sprites into one image, why not pack them all in the form of a sprite sheet?

So to summarize, image files when loaded into the graphics card must be power-of-two and square. However, the program can choose to render an arbitrary rectangle of that texture to the screen; it doesn't have to be power-of-two or square. So, pack the texture with multiple images to make the most efficient use of texture space.

回答3:

• Sprite sheets tend to be smaller files (since there's only 1 header for the whole lot.)
• Sprite sheets load quicker as there's just one disk access rather than several
• You can easily view or adjust multiple frames at once
• Less wasted video memory when you load the whole lot into one surface (as Ricket has said)
• Individual sprites can be delineated by offsets (eg. on an implicit grid - no need to explicitly mark or note each sprite's position)

There isn't a massive benefit for using sprite sheets, but several small ones. But the practice dates back to a time before most people were using proper 2D graphics software to make game graphics so the artist workflow wasn't necessarily the most important thing back then.