LibImage: Implement image resize using nearest or bilinear filters

LibImage/include/LibImage/Image.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <BAN/Limits.h>
 #include <BAN/StringView.h>
 #include <BAN/UniqPtr.h>
 #include <BAN/Vector.h>
@@ -16,24 +17,61 @@ namespace LibImage
 			uint8_t g;
 			uint8_t b;
 			uint8_t a;
+
+			// Calculate weighted average of colors
+			//   weight of 0.0 returns a and weight of 1.0 returns b
+			static Color average(Color a, Color b, double weight)
+			{
+				const double b_mult = BAN::Math::clamp(weight, 0.0, 1.0);
+				const double a_mult = 1.0 - b_mult;
+				return Color {
+					.r = static_cast<uint8_t>(a.r * a_mult + b.r * b_mult),
+					.g = static_cast<uint8_t>(a.g * a_mult + b.g * b_mult),
+					.b = static_cast<uint8_t>(a.b * a_mult + b.b * b_mult),
+					.a = static_cast<uint8_t>(a.a * a_mult + b.a * b_mult),
+				};
+			}
+		};
+
+		enum class ResizeAlgorithm
+		{
+			Nearest,
+			Bilinear,
 		};
 
 	public:
 		static BAN::ErrorOr<BAN::UniqPtr<Image>> load_from_file(BAN::StringView path);
 
+		BAN::ErrorOr<BAN::UniqPtr<Image>> resize(uint64_t new_width, uint64_t new_height, ResizeAlgorithm = ResizeAlgorithm::Bilinear);
+
 		Color get_color(uint64_t x, uint64_t y) const { return m_bitmap[y * width() + x]; }
 		const BAN::Vector<Color> bitmap() const { return m_bitmap; }
 
 		uint64_t width() const { return m_width; }
 		uint64_t height() const { return m_height; }
 
+		static constexpr bool validate_size(uint64_t width, uint64_t height)
+		{
+			// width and height must fit in int64_t and width * height * sizeof(Color) has to not overflow
+			if (width > static_cast<uint64_t>(BAN::numeric_limits<int64_t>::max()))
+				return false;
+			if (height > static_cast<uint64_t>(BAN::numeric_limits<int64_t>::max()))
+				return false;
+			if (BAN::Math::will_multiplication_overflow(width, height))
+				return false;
+			if (BAN::Math::will_multiplication_overflow(width * height, sizeof(Color)))
+				return false;
+			return true;
+		}
+
 	private:
 		Image(uint64_t width, uint64_t height, BAN::Vector<Color>&& bitmap)
 			: m_width(width)
 			, m_height(height)
 			, m_bitmap(BAN::move(bitmap))
 		{
-			ASSERT(m_bitmap.size() >= width * height);
+			ASSERT(validate_size(m_width, m_height));
+			ASSERT(m_bitmap.size() >= m_width * m_height);
 		}
 
 	private: