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[Impeller] reduce gaussian sampling by 2x #40871

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Apr 4, 2023
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[Impeller] reduce gaussian sampling by 2x #40871

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[Impeller] reduce gaussian sampling by 2x
Apr 2, 2023
4dc8833
patch malioc
Apr 3, 2023
7c19f90
bdero review
Apr 3, 2023
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Apr 3, 2023
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4 changes: 3 additions & 1 deletion impeller/entity/contents/filters/gaussian_blur_filter_contents.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -195,7 +195,7 @@ std::optional<Entity> DirectionalGaussianBlurFilterContents::RenderFilter(
FS::BlurInfo frag_info;
auto r = Radius{transformed_blur_radius_length};
frag_info.blur_sigma = Sigma{r}.sigma;
frag_info.blur_radius = r.radius;
frag_info.blur_radius = std::round(r.radius);

// The blur direction is in input UV space.
frag_info.blur_uv_offset =
Expand Down Expand Up @@ -240,6 +240,8 @@ std::optional<Entity> DirectionalGaussianBlurFilterContents::RenderFilter(
source_descriptor.height_address_mode = SamplerAddressMode::kRepeat;
break;
}
input_descriptor.mag_filter = MinMagFilter::kLinear;
input_descriptor.min_filter = MinMagFilter::kLinear;

bool has_alpha_mask = blur_style_ != BlurStyle::kNormal;
bool has_decal_specialization =
Expand Down
23 changes: 16 additions & 7 deletions impeller/entity/shaders/gaussian_blur/gaussian_blur.glsl
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Original file line number Diff line number Diff line change
Expand Up @@ -60,14 +60,23 @@ void main() {
f16vec4 total_color = f16vec4(0.0hf);
float16_t gaussian_integral = 0.0hf;

for (float16_t i = -blur_info.blur_radius; i <= blur_info.blur_radius; i++) {
float16_t gaussian = IPGaussian(i, blur_info.blur_sigma);
for (float16_t i = -blur_info.blur_radius; i <= blur_info.blur_radius;
i += 2.0hf) {
float16_t w1 = IPGaussian(i, blur_info.blur_sigma);
float16_t w2 = IPGaussian(i + 1.0hf, blur_info.blur_sigma);
float16_t gaussian = w1 + w2;

f16vec2 offset_1 = blur_info.blur_uv_offset * i;
f16vec2 offset_2 = offset_1 + blur_info.blur_uv_offset;
vec2 pos_c1 = v_texture_coords + offset_1;
vec2 pos_c2 = v_texture_coords + offset_2;

vec2 coords = (w1 * pos_c1 + w2 * pos_c2) / gaussian;

gaussian_integral += gaussian;
total_color +=
gaussian * Sample(texture_sampler, // sampler
v_texture_coords + blur_info.blur_uv_offset *
i // texture coordinates
);
total_color += gaussian * Sample(texture_sampler, // sampler
coords // texture coordinates
);
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@bdero bdero Apr 3, 2023 •
edited
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Leveraging linear sampling is a great idea. :)

Instead of fanning out the two sides here, I think just taking the original and doing something like for (float16_t i = round(-blur_info.blur_radius); i <= blur_info.blur_radius; i += 2.hf) would be the same?

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@jonahwilliams jonahwilliams Apr 3, 2023

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should we just round in the contents so blur_radius is always integral?

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@bdero bdero Apr 3, 2023

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Yeah rounding on the CPU seems good

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@jonahwilliams jonahwilliams Apr 3, 2023

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Done

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@jonahwilliams jonahwilliams Apr 3, 2023

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oops, where did it go...

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@jonahwilliams jonahwilliams Apr 3, 2023

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oh nvm, its there

}

frag_color = total_color / gaussian_integral;
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