Parameters for Engine creation

[BStringhamVRSK]

I would like to modify the Engine::create() to accept an optional struct containing parameters describing buffer sizes. This would allow us to set memory usage needs at run-time, based on platform, scene size, etc., rather than recompiling the library.
Question:
Which buffer sizes make the most sense to expose? The candidates I've considered are the ones set by these values:

• CONFIG_COMMAND_BUFFERS_SIZE
• CONFIG_PER_FRAME_COMMANDS_SIZE
• CONFIG_PER_RENDER_PASS_ARENA_SIZE

Considerations:

• What would be considered valid ranges for these?
• I would expect to put the current values as the minimum (and default) values.
• Parameters would be passed in MB units

Thoughts?

EDIT: Just found these in Engine.h. Probably should include all of these as part of the configuration scheme? Maybe I'll just do the memory ones for now.

    // TODO: these should come from a configuration object
    static constexpr float  CONFIG_Z_LIGHT_NEAR            = 5;
    static constexpr float  CONFIG_Z_LIGHT_FAR             = 100;
    static constexpr size_t CONFIG_FROXEL_SLICE_COUNT      = 16;
    static constexpr bool   CONFIG_IBL_USE_IRRADIANCE_MAP  = false;

    static constexpr size_t CONFIG_PER_RENDER_PASS_ARENA_SIZE   = filament::CONFIG_PER_RENDER_PASS_ARENA_SIZE;
    static constexpr size_t CONFIG_PER_FRAME_COMMANDS_SIZE      = filament::CONFIG_PER_FRAME_COMMANDS_SIZE;
    static constexpr size_t CONFIG_MIN_COMMAND_BUFFERS_SIZE     = filament::CONFIG_MIN_COMMAND_BUFFERS_SIZE;
    static constexpr size_t CONFIG_COMMAND_BUFFERS_SIZE         = filament::CONFIG_COMMAND_BUFFERS_SIZE;

[pixelflinger]

FYI this is something we've been wanting to do for a while -- it has never been a priority though.

CONFIG_FROXEL_SLICE_COUNT should probably not be changed.
CONFIG_Z_LIGHT_NEAR and CONFIG_Z_LIGHT_FAR should be handled like other options on View, I don't think these should be an engine parameter.

For the memory ones, I agree though. The important ones are:
CONFIG_MIN_COMMAND_BUFFERS_SIZE this one is the backend command queue. The needed size will depends mostly on how many objects you have in the scene. I would say that if you find you have to increase this on mobile, there is probably a problem with your scene, i.e. you have too many objects / draw calls. CONFIG_COMMAND_BUFFERS_SIZE should always be 3*CONFIG_MIN_COMMAND_BUFFERS_SIZE -- this is so we can have up to 3 frames of overlap.

CONFIG_PER_FRAME_COMMANDS_SIZE and CONFIG_PER_RENDER_PASS_ARENA_SIZE are mostly used for the "high level" command buffer. Each command is 40 bytes I think. And again, its size depends on how many visible objects you have in the scene.

[romainguy]

It's tracked here and here.

[BStringhamVRSK]

Thanks for the feedback. I am close to having a pull request put together, which will only touch the memory configuration. I'll implement your recommendations.

The approach I'm taking adds an optional parameter to the Engine::create() call:

static Engine* create(Backend backend = Backend::DEFAULT,
        Platform* platform = nullptr, void* sharedGLContext = nullptr,
        const ConfigParams* configParams = nullptr);

If no configParams is provided, it will fall back to the default values indicated by FILAMENT_PER_RENDER_PASS_ARENA_SIZE_IN_MB, etc.

[romainguy]

The configuration should probably just be a struct passed by value? @pixelflinger would know what's best