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[Impeller] round scale for glyph atlas cache to 2 decimal places. #43752

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Jul 25, 2023
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[Impeller] round scale for glyph atlas cache to 2 decimal places. #43752

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[Impeller] round scale for glyph atlas cache to 1 decimal place.
Jul 18, 2023
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Jul 18, 2023
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Jul 21, 2023
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Merge branch 'main' of github.com:flutter/engine into round_text
Jul 24, 2023
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Merge branch 'main' of github.com:flutter/engine into round_text
Jul 25, 2023
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add some debugging help text
Jul 25, 2023
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10 changes: 8 additions & 2 deletions impeller/entity/contents/text_contents.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,11 @@ TextContents::TextContents() = default;

TextContents::~TextContents() = default;

// static
Scalar TextContents::RoundFontScale(Scalar value) {
return std::round(value * 10.0) / 10.0;

@bdero bdero Jul 18, 2023 •
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I think this snapping would need to be done on a logarithmic scale (apply log, apply snapping, invert log w/ exponential)? Also, the snapping precision would need to somehow incorporate the text frame's font size as well.

For example, the difference between 0.1 and 0.2 is potentially huge, getting worse as the given font size increases.

@jonahwilliams jonahwilliams Jul 18, 2023

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hmm thats a good point. I'll need to investigate this a bit more.

@jonahwilliams jonahwilliams Jul 21, 2023

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okay, after much thinking I've come up with an OK solution.... round to one decimal if the point size is < 25, Round to two decimals if > 50. 🤷‍♂️

}

void TextContents::SetTextFrame(const TextFrame& frame) {
frame_ = frame;
}
Expand Down Expand Up @@ -78,8 +83,9 @@ std::optional<Rect> TextContents::GetCoverage(const Entity& entity) const {
void TextContents::PopulateGlyphAtlas(
const std::shared_ptr<LazyGlyphAtlas>& lazy_glyph_atlas,
Scalar scale) {
lazy_glyph_atlas->AddTextFrame(frame_, scale);
scale_ = scale;
auto rounded = RoundFontScale(scale);
lazy_glyph_atlas->AddTextFrame(frame_, rounded);
scale_ = rounded;
}

bool TextContents::Render(const ContentContext& renderer,
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5 changes: 5 additions & 0 deletions impeller/entity/contents/text_contents.h
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Expand Up @@ -55,6 +55,11 @@ class TextContents final : public Contents {
const Entity& entity,
RenderPass& pass) const override;

/// @brief Round font scales from arbitrary floating point values
/// (2.4223123) to one decimal place (2.4). This ensures that small
/// transform changes do not invalidate glyphs unecessarily.
static Scalar RoundFontScale(Scalar value);

private:
TextFrame frame_;
Scalar scale_ = 1.0;
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7 changes: 7 additions & 0 deletions impeller/entity/entity_unittests.cc
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Expand Up @@ -2435,6 +2435,13 @@ TEST_P(EntityTest, ColorFilterContentsWithLargeGeometry) {
ASSERT_TRUE(OpenPlaygroundHere(entity));
}

TEST_P(EntityTest, TextContentsCeilsGlyphScaleToDecimal) {
ASSERT_EQ(TextContents::RoundFontScale(0.4321111f), 0.4f);
ASSERT_EQ(TextContents::RoundFontScale(0.5321111f), 0.5f);
ASSERT_EQ(TextContents::RoundFontScale(2.1f), 2.1f);
ASSERT_EQ(TextContents::RoundFontScale(0.0f), 0.0f);
}

} // namespace testing
} // namespace impeller

Expand Down