You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: dissolve.go
    path of file: ./repos/ebiten/examples/shader
    
    the code of the file until where you have to start completion: // Copyright 2020 The Ebiten Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the Lice
    
func Fragment(dstPos vec4, srcPos vec2, color vec4) vec4 {
	// Triangle wave to go 0-->1-->0...
	limit := abs(2*fract(Time/3) - 1)
	level := imageSrc3UnsafeAt(srcPos).x

	// Add a white border
	if limit-0.1 < level && level < limit {
		alpha := imageSrc0UnsafeAt(srcPos).w
		return vec4(alpha)
	}

	return step(limit, level) * imageSrc0UnsafeAt(srcPos)
}