L2M - Binding and Format Optimization

Lineage 2 Mobile is one of the top revenue games in Google Play. It is an MMORPG, made by NCSoft in Korea.
We worked for almost 4 months with almost of GameDev colleagues online and offline. We integrated optimizations from previous projects and also made new optimizations and also analyzed performance differences based on content changes to allow us to make well-informed choices to optimize that content.

This article will introduce 2 changes, one is related to Vulkan, and the other is related to general rendering.

Optimized Vertex / Index buffer bound

First, is an optimization related to binding. As you probably know, GLES is a state machine, so once bound, the vertex and index buffer state remain in place. Vulkan, in contrast, is not actually a state machine, instead the state is saved in a command buffer. So, in a command buffer if the same vertex or index buffer is used as during the command buffer recording, then it is okay to call bind just once.

Before - bind with both vertex / index buffer

After - bind without both vertex / index buffer

The engine will try not to bind the same vertex/index buffer from previous draw calls under proper conditions (i.e. same pipeline, same CommandBuffer, same frame number) since the Vertex and Index Buffers are already recorded in the Command Buffer for the coming draw.

We made a performance comparison, to check the same condition we fixed CPU and GPU frequency. It has a 1fps benefit.

Device	SM-G973F	API	Async Creation	Original
Chipset	Mali G76	FPS	42	40

Format Optimization

If it is possible to use a lower bitrate format, it can have benefits for performance...
We found ‘CustomDepthStencil’ texture had 4 color channels, but only 1 color channel is read on the shader side. In this case, it is okay to change from RGBA to only R and doing so can reduce bandwidth demands by a factor of four.

MaterialFloat Stencil = Texture2DSample(MobileSceneTextures.MobileCustomStencilTexture, MobileSceneTextures.MobileCustomStencilTextureSampler, UV).r * 255.0;
Stencil = floor(Stencil + 0.5);

After implementation, we can see the framebuffer color channel is changed as well. Even the color changes from gray to red, but as only 1 color channel is used, the final result is the same.

Original	After
MobileCustomStencil-1440x720 1 mips-B8G8R8A8_UNORM	2D Color Attachment 816-1440x720 1 mips-R8_UNORM

Device	SM-G973U	API	Vulkan R8	Vulkan Original
Chipset	Adreno 640	FPS	53	52

Sometimes changing to a format which has a low bitrate can help performance even if that change might eliminate some color data.
There is a ‘PostProcessMaterial’ pass, which is for drawing the characters’ outlines. We found it used 4xFP16, but it could be reduced to a packed 32 bit format because it is just used for drawing the outline.

Original	2D Color Attachment 29382 - 1736x824 1 mips - Rl6Gl6Bl6Al6_FLOAT
After	2D Color Attachment 28890 - 1736x824 1 mips - Rl1Gl1Bl0_FLOAT

Device	SM-G975F	API	Optimized	Original
Chipset	Mali G76	FPS	35	34

If we set maximum fps to 30, we can see the actual difference for GPU usage. It has a 2% benefit.

Device	SM-G975F	API	Optimized	Original
Chipset	Mali G76	GPU Usage	96.13	98.13

The scene result is not exactly the same, but the difference is hard to recognize. If we change the format for base rendering, it would be easy to recognize but as this is for drawing characters’ outline so it is usually hard to see.

When changing an asset format, it is wise to check that the format supports GPU Driver compression such as ARM AFBC or Qualcomm UWBC. If the format does not support compression, it could decrease performance.

Conclusion

We integrate all our optimizations, we get 2~4 fps to benefit compared with GLES.

Device	Chipset	Vulkan	GLES
S9 Mali(SM-G965F)	Mali G72	38	34
S10 Mali(SM-G975F)	Mali G76	43	41

On lower-end devices such as S8 it has more benefit. It is checked with max fps 30.

Device	Chipset	Vulkan	GLES
S8 Mali(SM-G955F)	Mali G71	26	18
S8 Adreno(SM-G955U)	Adreno 540	30	22

Both of these optimizations are fairly well known and it is easy to think each will have only minor benefits... We all like to find those huge optimizations which make a game run twice as fast - but those are rare, and, instead, diligently working through changes like these while not so glamorous is often the main opportunity to improve the user experience. Additionally, the ease of implementing these changes meant that it was a fully justified choice.

Thanks to the GameDev Engineers : Alon Or-bach, Aton Sinyavskiy, Dohyun Kim, Fedir Nekrasov, Igor Nazarov, Inae Kim, Joonyong Park, Junsik Kong, Lewis Gordon, Kostiantyn Drabeniuk, Munseong Kang, Nataliia Kozoriz, Oleksii Vasylenko, Serhii Pavliv, Seunghwan Lee