ebiten/examples/shader/water.go

// 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 License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//go:build ignore

package main

var Time float
var Cursor vec2
var ScreenSize vec2

func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
	srcOrigin, srcSize := imageSrcRegionOnTexture()
	pos := (texCoord - srcOrigin) / srcSize
	pos *= ScreenSize

	border := ScreenSize.y*0.6 + 4*cos(Time*3+pos.y/10)
	if pos.y < border {
		return imageSrc2UnsafeAt(texCoord)
	}

	// Convert a pixel to a texel by dividing by the texture size.
	// TODO: This is confusing. Add a function to treat pixels (#1431).
	srcTexSize := imageSrcTextureSize()
	xoffset := (4 / srcTexSize.x) * cos(Time*3+pos.y/10)
	yoffset := (20 / srcTexSize.y) * (1 + cos(Time*3+pos.y/40))
	bordertex := border / srcTexSize.y
	clr := imageSrc2At(vec2(
		texCoord.x+xoffset,
		-(texCoord.y+yoffset-srcOrigin.y)+bordertex*2+srcOrigin.y,
	)).rgb

	overlay := vec3(0.5, 1, 1)
	return vec4(mix(clr, overlay, 0.25), 1)
}