crt_lotte.go

package shader

import "github.com/hajimehoshi/ebiten/v2"

// CrtLotteKage is a CRT shader based on crt-lottes.glsl.
//
// Credits: Elias Daler https://github.com/eliasdaler/crten and Timothy Lottes.
var CrtLotteKage = []byte(`
//go:build ignore

/*
This is a port of a public domain crt-lottes shader written by Timothy Lottes.
Rewritten to Kage by Elias Daler. The license is still public domain.
The original source code can be found here: https://github.com/libretro/glsl-shaders/blob/master/crt/shaders/crt-lottes.glsl

Changes:

1. DO_BLOOM is assumed. If you don't want bloom, set BloomAmount to 0
2. Accureate linear gamma is used because it looks better
3. Clamp fix is removed - there's no need for it, I think

*/

package main

var TextureSize vec2 // input screen size (e.g. 256x244 for SNES)
var ScreenSize vec2  // output screen size (e.g. when rendering at 4x resolution it is 1024x976)

var HardScan float
var HardPix float
var WarpX float
var WarpY float
var MaskDark float
var MaskLight float
var ScaleInLinearGamma float
var ShadowMask float
var BrightBoost float
var HardBloomPix float
var HardBloomScan float
var BloomAmount float
var Shape float

//use instead of uniforms if you don't need runtime modifiability

/*const HardScan = -8.0
const HardPix = -3.0
const WarpX = 0.031
const WarpY = 0.041
const MaskDark = 0.5
const MaskLight = 1.5
const ShadowMask = 3.0
const BrightBoost = 1.0
const HardBloomPix = -1.5
const HardBloomScan = -2.0
const BloomAmount = 0.05
const Shape = 2.0*/

func ToLinear1(c float) float {
	if c <= 0.04045 {
		return c / 12.92
	}
	return pow((c+0.055)/1.055, 2.4)
}

func ToLinear(c vec3) vec3 {
	return vec3(ToLinear1(c.r), ToLinear1(c.g), ToLinear1(c.b))
}

// Linear to sRGB.
// Assuming using sRGB typed textures this should not be needed.
func ToSrgb1(c float) float {
	if c < 0.0031308 {
		return c * 12.92
	}
	return 1.055*pow(c, 0.41666) - 0.055
}

func ToSrgb(c vec3) vec3 {
	return vec3(ToSrgb1(c.r), ToSrgb1(c.g), ToSrgb1(c.b))
}

// Nearest emulated sample given floating point position and texel offset.
// Also zero's off screen.
func Fetch(pos vec2, off vec2) vec3 {
	pos = (floor(pos*TextureSize.xy+off) + vec2(0.5, 0.5)) / TextureSize.xy
	origin, size := imageSrcRegionOnTexture()
	pos = pos*size + origin // IMPORTANT: go back to atlas coordinates from texture coordinates which OpenGL uses
	return ToLinear(BrightBoost * imageSrc0At(pos.xy).rgb)
}

// Distance in emulated pixels to nearest texel.
func Dist(pos vec2) vec2 {
	pos = pos * TextureSize.xy
	return -((pos - floor(pos)) - vec2(0.5))
}

// 1D Gaussian.
func Gaus(pos float, scale float) float {
	return exp2(scale * pow(abs(pos), Shape))
}

// 3-tap Gaussian filter along horz line.
func Horz3(pos vec2, off float) vec3 {
	b := Fetch(pos, vec2(-1.0, off))
	c := Fetch(pos, vec2(0.0, off))
	d := Fetch(pos, vec2(1.0, off))
	dst := Dist(pos).x

	// Convert distance to weight.
	scale := HardPix
	wb := Gaus(dst-1.0, scale)
	wc := Gaus(dst+0.0, scale)
	wd := Gaus(dst+1.0, scale)

	// Return filtered sample.
	return (b*wb + c*wc + d*wd) / (wb + wc + wd)
}

// 5-tap Gaussian filter along horz line.
func Horz5(pos vec2, off float) vec3 {
	a := Fetch(pos, vec2(-2.0, off))
	b := Fetch(pos, vec2(-1.0, off))
	c := Fetch(pos, vec2(0.0, off))
	d := Fetch(pos, vec2(1.0, off))
	e := Fetch(pos, vec2(2.0, off))

	dst := Dist(pos).x
	// Convert distance to weight.
	scale := HardPix
	wa := Gaus(dst-2.0, scale)
	wb := Gaus(dst-1.0, scale)
	wc := Gaus(dst+0.0, scale)
	wd := Gaus(dst+1.0, scale)
	we := Gaus(dst+2.0, scale)

	// Return filtered sample.
	return (a*wa + b*wb + c*wc + d*wd + e*we) / (wa + wb + wc + wd + we)
}

// 7-tap Gaussian filter along horz line.
func Horz7(pos vec2, off float) vec3 {
	a := Fetch(pos, vec2(-3.0, off))
	b := Fetch(pos, vec2(-2.0, off))
	c := Fetch(pos, vec2(-1.0, off))
	d := Fetch(pos, vec2(0.0, off))
	e := Fetch(pos, vec2(1.0, off))
	f := Fetch(pos, vec2(2.0, off))
	g := Fetch(pos, vec2(3.0, off))

	dst := Dist(pos).x
	// Convert distance to weight.
	scale := HardBloomPix
	wa := Gaus(dst-3.0, scale)
	wb := Gaus(dst-2.0, scale)
	wc := Gaus(dst-1.0, scale)
	wd := Gaus(dst+0.0, scale)
	we := Gaus(dst+1.0, scale)
	wf := Gaus(dst+2.0, scale)
	wg := Gaus(dst+3.0, scale)

	// Return filtered sample.
	return (a*wa + b*wb + c*wc + d*wd + e*we + f*wf + g*wg) / (wa + wb + wc + wd + we + wf + wg)
}

// Return scanline weight.
func Scan(pos vec2, off float) float {
	dst := Dist(pos).y
	return Gaus(dst+off, HardScan)
}

// Return scanline weight for Bloom.
func BloomScan(pos vec2, off float) float {
	dst := Dist(pos).y

	return Gaus(dst+off, HardBloomScan)
}

// Allow nearest three lines to effect pixel.
func Tri(pos vec2) vec3 {
	a := Horz3(pos, -1.0)
	b := Horz5(pos, 0.0)
	c := Horz3(pos, 1.0)

	wa := Scan(pos, -1.0)
	wb := Scan(pos, 0.0)
	wc := Scan(pos, 1.0)

	return a*wa + b*wb + c*wc
}

// Small Bloom.
func Bloom(pos vec2) vec3 {
	a := Horz5(pos, -2.0)
	b := Horz7(pos, -1.0)
	c := Horz7(pos, 0.0)
	d := Horz7(pos, 1.0)
	e := Horz5(pos, 2.0)

	wa := BloomScan(pos, -2.0)
	wb := BloomScan(pos, -1.0)
	wc := BloomScan(pos, 0.0)
	wd := BloomScan(pos, 1.0)
	we := BloomScan(pos, 2.0)

	return a*wa + b*wb + c*wc + d*wd + e*we
}

// Distortion of scanlines, and end of screen alpha.
func Warp(pos vec2) vec2 {
	pos = pos*2.0 - 1.0
	pos *= vec2(1.0+(pos.y*pos.y)*WarpX, 1.0+(pos.x*pos.x)*WarpY)

	return pos*0.5 + 0.5
}

// Shadow mask.
func Mask(pos vec2) vec3 {
	mask := vec3(MaskDark, MaskDark, MaskDark)

	if ShadowMask == 1.0 {
		// Very compressed TV style shadow mask.
		line := MaskLight
		odd := 0.0

		if fract(pos.x*0.166666666) < 0.5 {
			odd = 1.0
		}
		if fract((pos.y+odd)*0.5) < 0.5 {
			line = MaskDark
		}

		pos.x = fract(pos.x * 0.333333333)

		if pos.x < 0.333 {
			mask.r = MaskLight
		} else if pos.x < 0.666 {
			mask.g = MaskLight
		} else {
			mask.b = MaskLight
		}

		mask *= line
	} else if ShadowMask == 2.0 {
		// Aperture-grille.
		pos.x = fract(pos.x * 0.333333333)

		if pos.x < 0.333 {
			mask.r = MaskLight
		} else if pos.x < 0.666 {
			mask.g = MaskLight
		} else {
			mask.b = MaskLight
		}
	} else if ShadowMask == 3.0 {
		// Stretched VGA style shadow mask (same as prior shaders).
		pos.x += pos.y * 3.0
		pos.x = fract(pos.x * 0.166666666)

		if pos.x < 0.333 {
			mask.r = MaskLight
		} else if pos.x < 0.666 {
			mask.g = MaskLight
		} else {
			mask.b = MaskLight
		}
	} else if ShadowMask == 4.0 {
		// VGA style shadow mask.
		pos.xy = floor(pos.xy * vec2(1.0, 0.5))
		pos.x += pos.y * 3.0
		pos.x = fract(pos.x * 0.166666666)

		if pos.x < 0.333 {
			mask.r = MaskLight
		} else if pos.x < 0.666 {
			mask.g = MaskLight
		} else {
			mask.b = MaskLight
		}
	}
	return mask
}

func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
	// Adjust the texture position to [0, 1].
	pos := texCoord
	origin, size := imageSrcRegionOnTexture()
	pos -= origin
	pos /= size

	pos = Warp(pos)
	outColor := Tri(pos)

	//Add Bloom
	outColor.rgb += Bloom(pos) * BloomAmount

	fragCoord := position.xy
	fragCoord.y = ScreenSize.y - fragCoord.y // in OpenGL, Y is pointing up

	if ShadowMask > 0.0 {
		outColor.rgb *= Mask(fragCoord * 1.000001)
	}

	return vec4(ToSrgb(outColor.rgb), 1.0)
	// return vec4(imageSrc0At(texCoord).rgb, 1.0)
}
`)

type CrtLotte struct {
	BaseShader
}

func (s *CrtLotte) Apply(screen *ebiten.Image, buffer *ebiten.Image) error {
	s.Lock()
	defer s.Unlock()

	s.Uniforms["ScreenSize"] = []float32{float32(screen.Bounds().Dx()), float32(screen.Bounds().Dy())}
	s.Uniforms["TextureSize"] = []float32{float32(buffer.Bounds().Dx()), float32(buffer.Bounds().Dy())}

	sop := &ebiten.DrawRectShaderOptions{}
	sop.GeoM.Scale(float64(screen.Bounds().Dx())/float64(buffer.Bounds().Dx()), float64(screen.Bounds().Dy())/float64(buffer.Bounds().Dy()))
	sop.Uniforms = s.Uniforms
	sop.Images[0] = buffer

	screen.Clear()
	screen.DrawRectShader(screen.Bounds().Dx(), screen.Bounds().Dy(), s.Shader, sop)

	return nil
}

func NewCrtLotte() (*CrtLotte, error) {
	shader, err := ebiten.NewShader(CrtLotteKage)
	if err != nil {
		return nil, err
	}

	s := &CrtLotte{
		BaseShader: BaseShader{
			Shader: shader,
			Uniforms: map[string]interface{}{
				"HardScan":      float32(-8),
				"HardPix":       float32(-3),
				"WarpX":         float32(0.031),
				"WarpY":         float32(0.041),
				"MaskDark":      float32(0.5),
				"MaskLight":     float32(1.5),
				"ShadowMask":    float32(3.0),
				"BrightBoost":   float32(1.0),
				"HardBloomPix":  float32(-1.5),
				"HardBloomScan": float32(-2.0),
				"BloomAmount":   float32(0.05),
				"Shape":         float32(2.0),
			},
		},
	}

	return s, nil
}