Add GradientPattern

(Implemented using Anthropic's Claude)

Author: samcan

src/main/scala/Pattern.scala

@@ -94,3 +94,27 @@ def stripeAtObject(
 ): color.Color = {
   patternAtShape(pattern, obj, worldPoint)
 }
+
+// Gradient pattern implementation using linear interpolation
+case class GradientPattern(
+    a: color.Color,
+    b: color.Color,
+    override val transform: matrix.Matrix = matrix.Matrix.identity()
+) extends Pattern(transform) {
+
+  def patternAt(point: tuple.Tuple): color.Color = {
+    // Get the fractional part of x coordinate for interpolation
+    val distance = point.x - math.floor(point.x)
+
+    // Linear interpolation between colors a and b
+    color.Color(
+      a.red + distance * (b.red - a.red),
+      a.green + distance * (b.green - a.green),
+      a.blue + distance * (b.blue - a.blue)
+    )
+  }
+
+  def withTransform(newTransform: matrix.Matrix): GradientPattern = {
+    GradientPattern(a, b, newTransform)
+  }
+}

src/test/scala/PatternSuite.scala

@@ -135,4 +135,41 @@ class PatternSuite extends munit.FunSuite {
 
     assertEquals(color.isEqual(c, expected), true)
   }
+
+  test("A gradient linearly interpolates between colors") {
+    val pattern = GradientPattern(white, black)
+
+    // At x=0, should be white
+    assertEquals(
+      color.isEqual(pattern.patternAt(tuple.makePoint(0, 0, 0)), white),
+      true
+    )
+
+    // At x=0.25, should be color(0.75, 0.75, 0.75)
+    assertEquals(
+      color.isEqual(
+        pattern.patternAt(tuple.makePoint(0.25, 0, 0)),
+        color.Color(0.75, 0.75, 0.75)
+      ),
+      true
+    )
+
+    // At x=0.5, should be color(0.5, 0.5, 0.5)
+    assertEquals(
+      color.isEqual(
+        pattern.patternAt(tuple.makePoint(0.5, 0, 0)),
+        color.Color(0.5, 0.5, 0.5)
+      ),
+      true
+    )
+
+    // At x=0.75, should be color(0.25, 0.25, 0.25)
+    assertEquals(
+      color.isEqual(
+        pattern.patternAt(tuple.makePoint(0.75, 0, 0)),
+        color.Color(0.25, 0.25, 0.25)
+      ),
+      true
+    )
+  }
 }