What is the range of RAM consumption for the typical 3D character in a video game?

Question

What is the average number of KB in memory for a 3D character? Granted, this will obviously be biased based on what game we're talking about. However, I am less interested in actual size in KB, and more interested in the range. Simply, a general idea.

I want to know this information, to compare it to my 2D game. Currently, my 2D game has an almost exact scale for how much RAM a character takes up in memory.

The current formula is this: 95KB * Number of Animations * Number of Frames * Number of Directions. So for example, if a character had an Idle Animation with 15 frames, and a Walk animation of 15 frames, and there were 4 directions the character could move, the character would take 11.4MB in memory.

3D Characters have to load their mesh, textures, and animations. 2D characters simply load a image. However, with hundreds of animations- I can only imagine the 2D character would eventually exceed the memory requirements of a 3D character.

I need to get a general idea of how many characters I should limit on screen, how I should load my characters and their animations in memory, etc. I get some performance hits when swapping out textures in memory, probably because they are large spritesheets. I do not know if not using spritesheets would fix this or not. I was always told "Sprite Sheets are good for performance."

What about 3D games? Any example would work, and it doesn't have to be a real range. I just want to know what I may be looking at. An example of a lower quality 3D game and an example of a higher quality 3D game would be perfect.

Answer 1

General idea is very simple - "how much it needs to be" and depends on your artistic needs. You can make a model in Minecraft style (just a few Kb) or go a full scale NVidia-quality character (hundreds of Mb).

Calculate your budget first, how much memory you can spend on a model, what kind of quality do you need. Then you can do the estimates if you can fit an acceptable quality model in. Perceived model quality also greatly affected by artistic skills of the maker and rendering (dynamic lighting, complex SSS and SSAO shaders, etc.).

Try to compare with similar games.

P.S. From personal experience with racing games models. Good car model can take from 400kb to 26mb with the quality totally unrelated to the models size.

Answer 2

First, we eyeball the memory requirements for a 3d model.

• Each polygon has three vertices.
• Each vertex consists of three coordinates.
• Each coordinate is a floating point value of 4 bytes (or a double of 8 bytes)

So the amount of memory used for a 3d model is polygons * 3 * 3 * 4 or polygons * 36 byte. When your graphic engine uses double-precision floating point values, the size gets doubled.

So how many polygons does a character need? That depends on your level of detail. The characters from Minecraft have just about 100 polygons. But in a game which aims for a highly realistic graphic style, the polygon count for a single character can be tens of thousands of polygons.

This is just the 3d mesh. What we also need is the texture which is a simple 2d graphic. Maybe you want to use multi-texturing with normal maps, specular maps etc. Each of them is another 2d graphic. The memory consumption of each of them is width * height * color-depth. How large the texture needs to be depends on your desired level of detail. When the object is displayed up close you need a much higher texture resolution than when it is always small and far away, so it is hard to say which texture resolution is appropriate for your specific game.

Then we need the texture coordinates for each polygon (which part of the texture is mapped to each polygon). These are again 3 floating-point or integer values per polygon, so another 12 byte per polygon, getting us to 48 bytes per polygon.

Now we have a 3d model with a texture standing in our game. What's needed now? Yes, animation! Compared to 2d sprites, animations for 3d models are rather cheap. You don't need a whole new 3d model for each animation frame. You usually just specify how whole parts of the 3d model move for each animation. You usually just define the end-points of keyframes and when your 3d engine excutes the motion, it interpolates the positions in-between. That means that the additional memory requirement for a whole animation sequence are usually just a few hundred to a few thousand bytes.

By the way: Usually, 3d models are not stored in RAM of the system but in the VRAM of the graphic card.