In unity 4.3 i have 30 objects as single sprite that get it from 30files(png). when the game start it make 30 draw calls.But when i use one file(png) that have 30 pictures and then i use sprite mode Multiple it make 1 draw call but it have more tris and verts.I don’t know which way that i should choose?
have anyone can explain? thanks!
Draw calls are directly proportional to the number of materials in the scene (To keep it simple). If you see 30 draw calls, it means your camera has to draw 30 times a frame. It is always good to have this number as a lower value because in MOST cases having less draw call means better performance because less work for the renderer. There are few materials which requires the camera to draw multiple time, a good example is transparency materials which has transparent shaders which would draw multiple times for a single instance of object.
Batching is a technique to reduce draw calls in game. What it does is it groups objects with same material and draw it in a single draw call, this way the performance on the renderer can be improved. But this cannot be done in all cases, for example if each individual object has animation attached or the scale value is varying or the size of the object is big (number of tris is more), it cannot be batched.
What is happening in your project is dynamic batching, you have only one material for all 30 objects by creating a sprite this way the draw calls are reduced, which is always the better method because having 30 files means you are allocating 30 different textures in memmory, which would be definitely higher compared to one single file. But make sure to keep this sprite size as low as 2048x2048 if you are targeting iphone and android phones because in most of the android phones and lower end iphones the max texture size supported is 2048x2048 (some even have 1024x1024 limit but i wonder if anyone are still targeting those phones.)
Number of time the camera has to render depends on the number of draw calls, similarly the amount of time taken for the renderer to complete drawing one material depends on the number of tris on the object. You can have 1000 objects with 2 tris each and 50 objects with 1000 tris each. though the number of draw calls in case one is 1000, it would be relatively faster than case 2 which has jus 50 draw calls, because in case 2 it takes more time for a single object to be drawn.
So I would vote for your second method. But jus curious how much is the verts before and after using sprites?