The Ray Tracer Challenge

Making a Gradient Pattern

A gradient pattern is like stripes, but instead of discrete steps from one color to the next, the function returns a blend of the two colors, linearly interpolating from one to the other as the x coordinate changes. If the first color is red, and the second is blue, the resulting gradient will look like this:

Add the following test to show how a basic linear gradient pattern ought to work.

features/patterns.feature

Scenario: A gradient linearly interpolates between colors
  Given pattern ← gradient_pattern(white, black)
  Then pattern_at(pattern, point(0, 0, 0)) = white
    And pattern_at(pattern, point(0.25, 0, ...