ebiten/examples/shader/lighting.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

	lightpos := vec3(Cursor, 50)
	lightdir := normalize(lightpos - vec3(pos, 0))
	normal := normalize(imageSrc1UnsafeAt(texCoord) - 0.5)
	const ambient = 0.25
	diffuse := 0.75 * max(0.0, dot(normal.xyz, lightdir))
	return imageSrc0UnsafeAt(texCoord) * (ambient + diffuse)
}