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a0a3bfbee7
When background-size specifies only a width, the missing height was computed as `(CSSPixels(1) / ratio) * width`. The intermediate `CSSPixels(1) / ratio` step truncates the inverse ratio and loses enough precision to produce a visible error in the final height for some ratios. Now we do the division in one step, so the full precision is preserved.
65 lines
3.5 KiB
C++
65 lines
3.5 KiB
C++
/*
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* Copyright (c) 2022, MacDue <macdue@dueutil.tech>
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* Copyright (c) 2024, Sam Atkins <sam@ladybird.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include "Sizing.h"
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namespace Web::CSS {
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// https://drafts.csswg.org/css-images/#default-sizing
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CSSPixelSize run_default_sizing_algorithm(
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Optional<CSSPixels> specified_width,
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Optional<CSSPixels> specified_height,
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SizeWithAspectRatio const& natural,
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CSSPixelSize default_size)
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{
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// If the specified size is a definite width and height, the concrete object size is given that width and height.
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if (specified_width.has_value() && specified_height.has_value())
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return CSSPixelSize { specified_width.value(), specified_height.value() };
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// If the specified size is only a width or height (but not both) then the concrete object size is given that specified width or height.
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// The other dimension is calculated as follows:
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if (specified_width.has_value() || specified_height.has_value()) {
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// 1. If the object has a natural aspect ratio,
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// the missing dimension of the concrete object size is calculated using that aspect ratio and the present dimension.
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if (natural.has_aspect_ratio() && !natural.aspect_ratio->might_be_saturated()) {
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if (specified_width.has_value())
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return CSSPixelSize { specified_width.value(), specified_width.value() / natural.aspect_ratio.value() };
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if (specified_height.has_value())
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return CSSPixelSize { specified_height.value() * natural.aspect_ratio.value(), specified_height.value() };
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}
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// 2. Otherwise, if the missing dimension is present in the object’s natural dimensions,
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// the missing dimension is taken from the object’s natural dimensions.
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if (specified_height.has_value() && natural.has_width())
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return CSSPixelSize { natural.width.value(), specified_height.value() };
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if (specified_width.has_value() && natural.has_height())
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return CSSPixelSize { specified_width.value(), natural.height.value() };
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// 3. Otherwise, the missing dimension of the concrete object size is taken from the default object size.
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if (specified_height.has_value())
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return CSSPixelSize { default_size.width(), specified_height.value() };
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if (specified_width.has_value())
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return CSSPixelSize { specified_width.value(), default_size.height() };
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VERIFY_NOT_REACHED();
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}
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// If the specified size has no constraints:
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// 1. If the object has a natural height or width, its size is resolved as if its natural dimensions were given as the specified size.
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if (natural.has_width() || natural.has_height())
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return run_default_sizing_algorithm(natural.width, natural.height, natural, default_size);
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// 2. Otherwise, its size is resolved as a contain constraint against the default object size.
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if (natural.has_aspect_ratio() && !natural.aspect_ratio->might_be_saturated()) {
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auto aspect_ratio = natural.aspect_ratio.value();
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if (default_size.is_empty())
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return default_size;
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auto default_width = default_size.width().to_double();
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auto default_height = default_size.height().to_double();
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if (aspect_ratio.to_double() >= default_width / default_height)
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return CSSPixelSize { default_size.width(), CSSPixels::nearest_value_for(default_width / aspect_ratio.to_double()) };
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return CSSPixelSize { CSSPixels::nearest_value_for(default_height * aspect_ratio.to_double()), default_size.height() };
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}
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return default_size;
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}
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}
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