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LibWeb: Remove implicit conversion from float and double to CSSPixels
In general it is not safe to convert any arbitrary floating-point value to CSSPixels. CSSPixels has a resolution of 0.015625, which for small values (e.g. scale factors between 0 and 1), can produce bad results if converted to CSSPixels then scaled back up. In the worst case values can underflow to zero and produce incorrect results.
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43 changed files with 248 additions and 221 deletions
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@ -9,6 +9,7 @@
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#pragma once
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#include <AK/Concepts.h>
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#include <AK/Debug.h>
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#include <AK/DistinctNumeric.h>
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#include <AK/Math.h>
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#include <AK/Traits.h>
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@ -74,16 +75,16 @@ public:
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m_value = static_cast<int>(value) << fractional_bits;
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}
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CSSPixels(float value)
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{
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if (!isnan(value))
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m_value = AK::clamp_to_int(value * fixed_point_denominator);
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}
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CSSPixels(double value)
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template<FloatingPoint F>
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explicit CSSPixels(F value)
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{
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if (!isnan(value))
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m_value = AK::clamp_to_int(value * fixed_point_denominator);
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// Note: The resolution of CSSPixels is 0.015625, so care must be taken when converting
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// floats/doubles to CSSPixels as small values (such as scale factors) can underflow to zero,
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// or otherwise produce inaccurate results (when scaled back up).
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if (m_value == 0 && value != 0)
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dbgln_if(LIBWEB_CSS_DEBUG, "CSSPixels: Conversion from float or double underflowed to zero");
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}
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template<Unsigned U>
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@ -217,6 +218,32 @@ public:
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constexpr CSSPixels abs() const { return from_raw(::abs(m_value)); }
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CSSPixels& scale_by(float value)
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{
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*this = CSSPixels(to_float() * value);
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return *this;
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}
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CSSPixels& scale_by(double value)
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{
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*this = CSSPixels(to_double() * value);
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return *this;
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}
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CSSPixels scaled(float value) const
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{
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auto result = *this;
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result.scale_by(value);
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return result;
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}
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CSSPixels scaled(double value) const
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{
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auto result = *this;
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result.scale_by(value);
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return result;
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}
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private:
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i32 m_value { 0 };
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};
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