shader.go

package fauxgl

import "math"

type Shader interface {
	Vertex(Vertex) Vertex
	Fragment(Vertex) Color
}

type DefaultShader struct {
	Matrix  Matrix
	Light   Vector
	Camera  Vector
	Color   Color
	Texture Texture
}

func NewDefaultShader(matrix Matrix, light, camera Vector, color Color) *DefaultShader {
	return &DefaultShader{matrix, light, camera, color, nil}
}

func (shader *DefaultShader) Vertex(v Vertex) Vertex {
	v.Output = shader.Matrix.MulPositionW(v.Position)
	return v
}

func (shader *DefaultShader) Fragment(v Vertex) Color {
	color := shader.Color
	if color == Discard {
		color = v.Color
	}
	if shader.Texture != nil {
		color = shader.Texture.BilinearSample(v.Texture.X, v.Texture.Y)
	}
	diffuse := math.Max(v.Normal.Dot(shader.Light), 0)
	specular := 0.0
	if diffuse > 0 {
		camera := shader.Camera.Sub(v.Position).Normalize()
		specular = math.Max(camera.Dot(shader.Light.Negate().Reflect(v.Normal)), 0)
		specular = math.Pow(specular, 50)
	}
	light := Clamp(diffuse+specular, 0.1, 1)
	return color.MulScalar(light).Alpha(color.A)
}

type SolidColorShader struct {
	Matrix Matrix
	Color  Color
}

func NewSolidColorShader(matrix Matrix, color Color) *SolidColorShader {
	return &SolidColorShader{matrix, color}
}

func (shader *SolidColorShader) Vertex(v Vertex) Vertex {
	v.Output = shader.Matrix.MulPositionW(v.Position)
	return v
}

func (shader *SolidColorShader) Fragment(v Vertex) Color {
	return shader.Color
}

type DiffuseShader struct {
	Matrix   Matrix
	LightDir Vector
	Color    Color
	Ambient  Color
	Diffuse  Color
}

func NewDiffuseShader(matrix Matrix, light Vector, color, ambient, diffuse Color) *DiffuseShader {
	return &DiffuseShader{matrix, light, color, ambient, diffuse}
}

func (shader *DiffuseShader) Vertex(v Vertex) Vertex {
	v.Output = shader.Matrix.MulPositionW(v.Position)
	return v
}

func (shader *DiffuseShader) Fragment(v Vertex) Color {
	color := shader.Color
	if color == Discard {
		color = v.Color
	}
	diffuse := math.Max(v.Normal.Dot(shader.LightDir), 0)
	light := shader.Ambient.Add(shader.Diffuse.MulScalar(diffuse))
	return color.Mul(light).Alpha(color.A)
}