ebiten: reland: use Kage shaders instead of built-in shaders for a color matrix

This replaces the built-in shaders with Kage shadres. This is a
refactoring and doesn't degrade performance:

```
go test -bench=^BenchmarkColorMScale$ -run=^$ . -count=5
```

```
name           old time/op  new time/op  delta
ColorMScale-8   978ns ±15%  1184ns ±46%   ~     (p=0.413 n=4+5)
```

A follow-up change to remove the built-in shaders is needed.

Closes #2364

image.go

@@ -21,6 +21,7 @@ import (
 
 	"github.com/hajimehoshi/ebiten/v2/internal/affine"
 	"github.com/hajimehoshi/ebiten/v2/internal/atlas"
+	"github.com/hajimehoshi/ebiten/v2/internal/builtinshader"
 	"github.com/hajimehoshi/ebiten/v2/internal/graphics"
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver"
 	"github.com/hajimehoshi/ebiten/v2/internal/ui"
@@ -231,7 +232,20 @@ func (i *Image) DrawImage(img *Image, options *DrawImageOptions) {
 
 	srcs := [graphics.ShaderImageCount]*ui.Image{img.image}
 
-	i.image.DrawTriangles(srcs, vs, is, colorm, mode, filter, graphicsdriver.AddressUnsafe, i.adjustedRegion(), graphicsdriver.Region{}, [graphics.ShaderImageCount - 1][2]float32{}, nil, nil, false, canSkipMipmap(options.GeoM, filter))
+	useColorM := !colorm.IsIdentity()
+	shader := builtinShader(graphicsdriver.Filter(filter), graphicsdriver.AddressUnsafe, useColorM)
+	var uniforms [][]float32
+	if useColorM {
+		var body [16]float32
+		var translation [4]float32
+		colorm.Elements(body[:], translation[:])
+		uniforms = shader.convertUniforms(map[string]interface{}{
+			builtinshader.UniformColorMBody:        body[:],
+			builtinshader.UniformColorMTranslation: translation[:],
+		})
+	}
+
+	i.image.DrawTriangles(srcs, vs, is, affine.ColorMIdentity{}, mode, graphicsdriver.FilterNearest, graphicsdriver.AddressUnsafe, i.adjustedRegion(), graphicsdriver.Region{}, [graphics.ShaderImageCount - 1][2]float32{}, shader.shader, uniforms, false, canSkipMipmap(options.GeoM, filter))
 }
 
 // Vertex represents a vertex passed to DrawTriangles.
@@ -426,7 +440,20 @@ func (i *Image) DrawTriangles(vertices []Vertex, indices []uint16, img *Image, o
 
 	srcs := [graphics.ShaderImageCount]*ui.Image{img.image}
 
-	i.image.DrawTriangles(srcs, vs, is, colorm, mode, filter, address, i.adjustedRegion(), sr, [graphics.ShaderImageCount - 1][2]float32{}, nil, nil, options.FillRule == EvenOdd, false)
+	useColorM := !colorm.IsIdentity()
+	shader := builtinShader(graphicsdriver.Filter(filter), graphicsdriver.Address(address), useColorM)
+	var uniforms [][]float32
+	if useColorM {
+		var body [16]float32
+		var translation [4]float32
+		colorm.Elements(body[:], translation[:])
+		uniforms = shader.convertUniforms(map[string]interface{}{
+			builtinshader.UniformColorMBody:        body[:],
+			builtinshader.UniformColorMTranslation: translation[:],
+		})
+	}
+
+	i.image.DrawTriangles(srcs, vs, is, affine.ColorMIdentity{}, mode, graphicsdriver.FilterNearest, graphicsdriver.AddressUnsafe, i.adjustedRegion(), sr, [graphics.ShaderImageCount - 1][2]float32{}, shader.shader, uniforms, options.FillRule == EvenOdd, false)
 }
 
 // DrawTrianglesShaderOptions represents options for DrawTrianglesShader.

internal/builtinshader/shader.go

@@ -0,0 +1,150 @@
+// Copyright 2022 The Ebitengine 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.
+
+package builtinshader
+
+import (
+	"bytes"
+	"fmt"
+	"sync"
+	"text/template"
+
+	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver"
+)
+
+const (
+	UniformColorMBody        = "ColorMBody"
+	UniformColorMTranslation = "ColorMTranslation"
+)
+
+type key struct {
+	Filter    graphicsdriver.Filter
+	Address   graphicsdriver.Address
+	UseColorM bool
+}
+
+var (
+	shaders  = map[key][]byte{}
+	shadersM sync.Mutex
+)
+
+var tmpl = template.Must(template.New("tmpl").Parse(`package main
+
+{{if .UseColorM}}
+var ColorMBody mat4
+var ColorMTranslation vec4
+{{end}}
+
+{{if eq .Address .AddressRepeat}}
+func adjustTexelForAddressRepeat(p vec2) vec2 {
+	origin, size := imageSrcRegionOnTexture()
+	return mod(p - origin, size) + origin
+}
+{{end}}
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+{{if eq .Filter .FilterNearest}}
+{{if eq .Address .AddressUnsafe}}
+	clr := imageSrc0UnsafeAt(texCoord)
+{{else if eq .Address .AddressClampToZero}}
+	clr := imageSrc0At(texCoord)
+{{else if eq .Address .AddressRepeat}}
+	clr := imageSrc0At(adjustTexelForAddressRepeat(texCoord))
+{{end}}
+{{else if eq .Filter .FilterLinear}}
+	sourceSize := imageSrcTextureSize()
+	texelSize := 1 / sourceSize
+
+	// Shift 1/512 [texel] to avoid the tie-breaking issue (#1212).
+	// As all the vertex positions are aligned to 1/16 [pixel], this shiting should work in most cases.
+	p0 := texCoord - texelSize/2 + texelSize/512
+	p1 := texCoord + texelSize/2 + texelSize/512
+
+{{if eq .Address .AddressRpeat}}
+	p0 = adjustTexelForAddressRepeat(p0)
+	p1 = adjustTexelForAddressRepeat(p1)
+{{end}}
+
+{{if eq .Address .AddressUnsafe}}
+	c0 := imageSrc0UnsafeAt(p0)
+	c1 := imageSrc0UnsafeAt(vec2(p1.x, p0.y))
+	c2 := imageSrc0UnsafeAt(vec2(p0.x, p1.y))
+	c3 := imageSrc0UnsafeAt(p1)
+{{else}}
+	c0 := imageSrc0At(p0)
+	c1 := imageSrc0At(vec2(p1.x, p0.y))
+	c2 := imageSrc0At(vec2(p0.x, p1.y))
+	c3 := imageSrc0At(p1)
+{{end}}
+
+	rate := fract(p0 * sourceSize)
+	clr := mix(mix(c0, c1, rate.x), mix(c2, c3, rate.x), rate.y)
+{{end}}
+
+{{if .UseColorM}}
+	// Un-premultiply alpha.
+	// When the alpha is 0, 1-sign(alpha) is 1.0, which means division does nothing.
+	clr.rgb /= clr.a + (1-sign(clr.a))
+	// Apply the clr matrix or scale.
+	clr = (ColorMBody * clr) + ColorMTranslation
+	// Premultiply alpha
+	clr.rgb *= clr.a
+	// Apply the color scale.
+	clr *= color
+	// Clamp the output.
+	clr.rgb = min(clr.rgb, clr.a)
+{{else}}
+	// Apply the color scale.
+	clr *= color
+{{end}}
+
+	return clr
+}
+
+`))
+
+// Shader returns the built-in shader based on the given parameters.
+//
+// The returned shader always uses a color matrix so far.
+func Shader(filter graphicsdriver.Filter, address graphicsdriver.Address, useColorM bool) []byte {
+	shadersM.Lock()
+	defer shadersM.Unlock()
+
+	k := key{
+		Filter:    filter,
+		Address:   address,
+		UseColorM: useColorM,
+	}
+	if s, ok := shaders[k]; ok {
+		return s
+	}
+
+	var buf bytes.Buffer
+	if err := tmpl.Execute(&buf, map[string]interface{}{
+		"Filter":             filter,
+		"FilterNearest":      graphicsdriver.FilterNearest,
+		"FilterLinear":       graphicsdriver.FilterLinear,
+		"Address":            address,
+		"AddressUnsafe":      graphicsdriver.AddressUnsafe,
+		"AddressClampToZero": graphicsdriver.AddressClampToZero,
+		"AddressRepeat":      graphicsdriver.AddressRepeat,
+		"UseColorM":          useColorM,
+	}); err != nil {
+		panic(fmt.Sprintf("builtinshader: tmpl.Execute failed: %v", err))
+	}
+
+	b := buf.Bytes()
+	shaders[k] = b
+	return b
+}

shader.go

@@ -15,7 +15,12 @@
 package ebiten
 
 import (
+	"fmt"
+	"sync"
+
+	"github.com/hajimehoshi/ebiten/v2/internal/builtinshader"
 	"github.com/hajimehoshi/ebiten/v2/internal/graphics"
+	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver"
 	"github.com/hajimehoshi/ebiten/v2/internal/ui"
 )
 
@@ -51,3 +56,36 @@ func (s *Shader) Dispose() {
 func (s *Shader) convertUniforms(uniforms map[string]interface{}) [][]float32 {
 	return s.shader.ConvertUniforms(uniforms)
 }
+
+type builtinShaderKey struct {
+	filter    graphicsdriver.Filter
+	address   graphicsdriver.Address
+	useColorM bool
+}
+
+var (
+	builtinShaders  = map[builtinShaderKey]*Shader{}
+	builtinShadersM sync.Mutex
+)
+
+func builtinShader(filter graphicsdriver.Filter, address graphicsdriver.Address, useColorM bool) *Shader {
+	builtinShadersM.Lock()
+	defer builtinShadersM.Unlock()
+
+	key := builtinShaderKey{
+		filter:    filter,
+		address:   address,
+		useColorM: useColorM,
+	}
+	if s, ok := builtinShaders[key]; ok {
+		return s
+	}
+
+	src := builtinshader.Shader(filter, address, useColorM)
+	s, err := NewShader(src)
+	if err != nil {
+		panic(fmt.Sprintf("ebiten: NewShader for a built-in shader failed: %v", err))
+	}
+	builtinShaders[key] = s
+	return s
+}