Two-color angle gradient in Core Image

gistfile1.txt

kernel vec4 coreImageKernel(__color startColor, __color endColor)
{
	vec2 point = destCoord();

	float angle = atan(point.y, point.x) + radians(180.0);
	//Start from the upper middle, not the left middle
	angle += radians(90.0);
	angle = mod(angle, radians(360.0));

	float fraction = angle / radians(360.0);

	vec4 resultColor = startColor * (1.0 - fraction) + endColor * fraction;
	return resultColor;
}