LibPDF: Add first interpolation methods

Interpolation is needed in more than one place, and I couldn't find a
central place where I could borrow a readily available interpolation
routine, so I've implemented the first simple interpolation object. More
will follow for more complex scenarios.

Userland/Libraries/LibPDF/CMakeLists.txt

@@ -11,6 +11,7 @@ set(SOURCES
     Fonts/TrueTypeFont.cpp
     Fonts/Type0Font.cpp
     Fonts/Type1Font.cpp
+    Interpolation.cpp
     ObjectDerivatives.cpp
     Parser.cpp
     Reader.cpp

Userland/Libraries/LibPDF/Interpolation.cpp

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2022, Rodrigo Tobar <rtobarc@gmail.com>.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibPDF/Interpolation.h>
+
+namespace PDF {
+
+static float slope(float x_min, float x_max, float y_min, float y_max)
+{
+    return (y_max - y_min) / (x_max - x_min);
+}
+
+LinearInterpolation1D::LinearInterpolation1D(float x_min, float x_max, float y_min, float y_max)
+    : m_x_min(x_min)
+    , m_y_min(y_min)
+    , m_slope(slope(x_min, x_max, y_min, y_max))
+{
+}
+
+float LinearInterpolation1D::interpolate(float x) const
+{
+    return m_y_min + ((x - m_x_min) * m_slope);
+}
+
+void LinearInterpolation1D::interpolate(Span<float> const& x, Span<float> y) const
+{
+    for (size_t i = 0; i < x.size(); ++i) {
+        y[i] = interpolate(x[i]);
+    }
+}
+
+}

Userland/Libraries/LibPDF/Interpolation.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2022, Rodrigo Tobar <rtobarc@gmail.com>.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Span.h>
+#include <AK/Vector.h>
+
+namespace PDF {
+
+class LinearInterpolation1D {
+
+public:
+    LinearInterpolation1D(float x_min, float x_max, float y_min, float y_max);
+    float interpolate(float) const;
+    void interpolate(Span<float> const& x, Span<float> y) const;
+
+private:
+    float m_x_min;
+    float m_y_min;
+    float m_slope;
+};
+
+}