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I have a question regarding performance and how game engines handle mesh objects. – For the purpose of this question, let’s assume we have a wall asset within a game. If we make our wall 10 feet tall and 100 feet long, we have a rectangle, which can be made up of two large triangles.

So, our first example is a wall that is 10 feet tall X 100 feet long and is made up of 2 triangles.

Let’s now assume we broke up that same wall into smaller 10 foot sections (i.e. 10 feet tall X 10 feet long each).

So, in our second example we have our 100 foot long wall made up of 10 individual sections, which are each 10' x 10' made up or 2 triangles**each**, so our 100 foot wall now contains 20 triangles.

__In recap__:

Example 1 = A wall, 10 feet tall X 100 feet long and is made up of 2 triangles.

Example 2 = A wall made up of 10 sections, each at 10 feet tall x10 feet long and each section is made up or 2 triangles, so our wall has a total of 20 triangles.

My question is which of these designs approaches to our wall is more memory intensive for the game engine to deliver to the scene?

Is it more expensive (in terms of memory resources) to draw 2 very large triangles. Or, is it more expensive to draw 20 much smaller triangles?

Or are they equivalent…after all, we’re producing the same asset which is 10 feet tall and 100 feet long? The only difference is that in one instance we're drawing 2 huge triangles and in the other we're drawing 20 much smaller triangles. Can we assume each triangle is 1 "**draw-call**"? Or is that something totally different?

Although this may seem somewhat academic in terms of "one wall", it can add up when you're producing "modular" assets for a city scene or for a large office building scene or modular asset.

Thank you,

Fulano

So, our first example is a wall that is 10 feet tall X 100 feet long and is made up of 2 triangles.

Let’s now assume we broke up that same wall into smaller 10 foot sections (i.e. 10 feet tall X 10 feet long each).

So, in our second example we have our 100 foot long wall made up of 10 individual sections, which are each 10' x 10' made up or 2 triangles

Example 1 = A wall, 10 feet tall X 100 feet long and is made up of 2 triangles.

Example 2 = A wall made up of 10 sections, each at 10 feet tall x10 feet long and each section is made up or 2 triangles, so our wall has a total of 20 triangles.

My question is which of these designs approaches to our wall is more memory intensive for the game engine to deliver to the scene?

Is it more expensive (in terms of memory resources) to draw 2 very large triangles. Or, is it more expensive to draw 20 much smaller triangles?

Or are they equivalent…after all, we’re producing the same asset which is 10 feet tall and 100 feet long? The only difference is that in one instance we're drawing 2 huge triangles and in the other we're drawing 20 much smaller triangles. Can we assume each triangle is 1 "

Although this may seem somewhat academic in terms of "one wall", it can add up when you're producing "modular" assets for a city scene or for a large office building scene or modular asset.

Thank you,

Fulano

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For memory usage, you want to think in terms of "textures" - which basically means a bitmap image. Those are loaded into the GPU and will consume memory. The more detail in the image (the more pixels) the more memory required.

Once you have the texture loaded, then you can issue draw calls to render that texture somewhere on the screen - e.g. onto your wall made up of 2 triangles.

If you take the texture and render it 20 times or 2 times, it's the same memory usage. But rendering 20 smaller images may require more CPU/GPU time because there's more draw calls.

Also you can take one texture and stretch it during the drawing. Let's imagine your wall is flat - so we'll ignore any 3D rotations etc. If the wall was 1000 pixels x 1000 pixels on the user's screen and your texture was 100 pixels x 100 pixels, then you could:

a) Stretch the texture 10x10 to cover the entire wall (1 draw call, no extra memory)

or

b) Render the texture at 1:1 and draw it 100 times to cover the entire wall (100 draw calls, no extra memory)

(b) will take more time, but also look a lot better (a lot higher res) than (a) which is a stretched texture (so it'll look blurry on screen).

If you want approach (a) to look as good as (b) - you could also load a texture that's 100 times as big (1000 pixels x 1000 pixels) and render that directly without stretching it (1 draw call, 100 times the memory).

At least that's my take on how this works.

Hope that helps a bit,

Doug

It's sort of the old CPU vs RAM tradeoff that we're used to in many other parts of computing. And also in this case quality vs speed. (Higher polygons -> higher quality, but lower speed).

So definitely important to consider, but I think it's more about CPU cycles (or GPU cycles) rather than memory in this case. Both are of course a limited resource and their use should be considered carefully.

Doug

So lets say you have your game running on a mobile device thats a few generations old and pretty slow. A scene where it loads a giant wall, there is only only three faces it has to draw with large single wall with two triangles (assuming the angle of the camera sees top, and two sides, if you figure out how to see more sides than that let me know). However the wall made up of many objects will have more faces to render, and therefore tax it more. Alternatively, there would be almost no difference in the large single wall with 2 triangles or 20, but of course, at a certain point increasing the mesh polly count to a drastic degree would eventually make a performance hit.

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