Does the scale of a background image affect performance?

Question

I have a background that's a half-square shape.

If I increase the size of the background, for example by adjusting the scale of the model from 1x to 10000x, will this affect the performance of the game?

Answer 1

No, scale should not affect performance as a general rule.

Under the hood, scale is handled as part of the matrix multiplication in the graphics pipeline that transforms vertices from model space to screen space. This matrix multiplication happens no matter what scale value you use, and multiplying by 1 has the same cost as multiplying by 1000, so increasing the scale number itself does not cost anything extra.

There are two potential exceptions, where increasing scale has a side effect that can affect performance, but they should not apply to your case:

• When an object gets bigger, it can occupy more pixels on the screen. That means the pixel shader of its material gets invoked more times, and you spend more of your fill rate (the maximum number of times your GPU can write a pixel value into an output buffer in a unit of time) drawing it. For an expensive shader, or cases where your game is fill rate bound, this can affect performance.

  In your case, since a background image is usually covering the whole screen anyway, you should not observe a difference due to this effect.

• When an object has a physics collider, that collider needs to be sorted into acceleration structures to optimize collision checks and physics calculations. When objects are very very large, it's harder to cull them during collision checking because they could potentially be touching so many places in your scene. That can increase processing costs.

  Large and heavy objects can also make some collision and constraint resolution calculations less stable - especially when they collide with much smaller/lighter objects, and this can cause visible jitters or glitches. Usually physics engines are optimized to work best with objects ranging from a few tenths of units to tens of units in size, so keeping most objects in this range can be good for stability.

  But again, in your case, background images usually don't have any physics associated with them, so you should not expect this to apply here.

Overall, the very best way to find out how something affects performance in your game, running on your target hardware, is to try it and use the profiler to measure the impact. This will get you verifiable evidence, rather than hearsay from strangers on the Internet, so always make this your go-to method for learning about your game's performance.