[Impeller] migrate blur to calculating coefficients on the cpu

[gaaclarke]

issue: flutter/flutter#131580

This factors out the gaussian blur fragment shader to be a more generic kernel fragment shader. We can't use this for the old gaussian blur because it's kernel is unbounded in one dimension. I implemented this by passing in the coefficients into the UBO so it can't support that.

Profile after change:

    "average_vsync_transitions_missed": 2.0,
    "90th_percentile_vsync_transitions_missed": 2.0,
    "99th_percentile_vsync_transitions_missed": 2.0,
    "average_vsync_frame_lag": 0.0,
    "90th_percentile_vsync_frame_lag": 0.0,
    "99th_percentile_vsync_frame_lag": 0.0,
    "average_layer_cache_count": 0.0,
    "90th_percentile_layer_cache_count": 0.0,
    "99th_percentile_layer_cache_count": 0.0,
    "average_frame_request_pending_latency": 16636.624373956594,
    "90th_percentile_frame_request_pending_latency": 16718.0,
    "99th_percentile_frame_request_pending_latency": 16761.0,
    "worst_layer_cache_count": 0.0,
    "average_layer_cache_memory": 0.0,
    "90th_percentile_layer_cache_memory": 0.0,
    "99th_percentile_layer_cache_memory": 0.0,
    "worst_layer_cache_memory": 0.0,
    "average_picture_cache_count": 0.0,
    "90th_percentile_picture_cache_count": 0.0,
    "99th_percentile_picture_cache_count": 0.0,
    "worst_picture_cache_count": 0.0,
    "average_picture_cache_memory": 0.0,
    "90th_percentile_picture_cache_memory": 0.0,
    "99th_percentile_picture_cache_memory": 0.0,
    "worst_picture_cache_memory": 0.0,
    "total_ui_gc_time": 1.65,
    "30hz_frame_percentage": 0.0,
    "60hz_frame_percentage": 100.0,
    "80hz_frame_percentage": 0.0,
    "90hz_frame_percentage": 0.0,
    "120hz_frame_percentage": 0.0,
    "illegal_refresh_rate_frame_count": 0,
    "average_gpu_frame_time": 21.875,
    "90th_percentile_gpu_frame_time": 31.25,
    "99th_percentile_gpu_frame_time": 31.25,
    "worst_gpu_frame_time": 31.25,
    "average_cpu_usage": 162.86326532653064,
    "90th_percentile_cpu_usage": 167.3,
    "99th_percentile_cpu_usage": 168.500003,
    "average_gpu_usage": 93.26530612244898,
    "90th_percentile_gpu_usage": 94.0,
    "99th_percentile_gpu_usage": 95.0,
    "average_memory_usage": 113.56696428571429,
    "90th_percentile_memory_usage": 145.484375,
    "99th_percentile_memory_usage": 152.75

This is a 13% (21.25 / 25 ) drop in average_gpu_frame_time from the last profile in #49299.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide and the C++, Objective-C, Java style guides.
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or the PR is test-exempt. See testing the engine for instructions on writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
• I signed the CLA.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[jonahwilliams]

LGTM

Uber-nit: kernel as a name is sort of ambiguous. If we're able to get rid of the old gaussian, can we reclaim that name later?

[gaaclarke]

Uber-nit: kernel as a name is sort of ambiguous. If we're able to get rid of the old gaussian, can we reclaim that name later?

Here's the thinking behind it. The fragment shader, by virtue of removing all the blur math, was left with just applying a Kernel. It's exactly the name for what it does. There are a few effects that can be implemented with just a Kernel and given Impeller's ethos of having a limited static set of shaders, it made more sense, to me, to make it available for everyone instead of naming it something specific.