Transforms a position from window to eye coordinates.
The transform from window to normalized device coordinates is done using components
of (@link czm_viewport} and czm_viewportTransformation instead of calculating
the inverse of
czm_viewportTransformation. The transformation from
normalized device coordinates to clip coordinates is done using positionWC.w,
which is expected to be the scalar used in the perspective divide. The transformation
from clip to eye coordinates is done using czm_inverseProjection.Example
vec4 positionEC = czm_windowToEyeCoordinates(gl_FragCoord);