internal/shaderir/glsl: Bug fix: Remove uncalled functions

Some built-in functions like dFdx is not available in a vertex shader,
then a function that calls such built-in function should not be in
a vertex shader.

Closes #1701

internal/shader/testdata/issue1701.expected.fs

@@ -0,0 +1,15 @@
+void F2(void);
+void F3(void);
+
+void F2(void) {
+}
+
+void F3(void) {
+	F2();
+}
+
+void main(void) {
+	F3();
+	gl_FragColor = vec4(0.0);
+	return;
+}

internal/shader/testdata/issue1701.expected.vs

@@ -0,0 +1,29 @@
+attribute vec2 A0;
+
+void F0(void);
+void F1(void);
+void F2(void);
+void F3(void);
+
+void F0(void) {
+	F1();
+	F2();
+}
+
+void F1(void) {
+	F2();
+	F3();
+}
+
+void F2(void) {
+}
+
+void F3(void) {
+	F2();
+}
+
+void main(void) {
+	F0();
+	gl_Position = vec4(0.0);
+	return;
+}

internal/shader/testdata/issue1701.go

@@ -0,0 +1,35 @@
+package main
+
+func Foo() {
+	Bar()
+	Baz()
+}
+
+func Bar() {
+	Baz()
+	Quux()
+}
+
+func Baz() {
+}
+
+func Quux() {
+	Baz()
+}
+
+func NeverCalled() {
+	Foo()
+	Bar()
+	Baz()
+	Quux()
+}
+
+func Vertex(pos vec2) vec4 {
+	Foo()
+	return vec4(0)
+}
+
+func Fragment(pos vec4) vec4 {
+	Quux()
+	return vec4(0)
+}

internal/shaderir/glsl/glsl.go

@@ -19,6 +19,7 @@ import (
 	"go/constant"
 	"go/token"
 	"regexp"
+	"sort"
 	"strings"
 
 	"github.com/hajimehoshi/ebiten/v2/internal/shaderir"
@@ -82,6 +83,12 @@ func Compile(p *shaderir.Program, version GLSLVersion) (vertexShader, fragmentSh
 		structNames: map[string]string{},
 	}
 
+	indexToFunc := map[int]*shaderir.Func{}
+	for _, f := range p.Funcs {
+		f := f
+		indexToFunc[f.Index] = &f
+	}
+
 	// Vertex func
 	var vslines []string
 	{
@@ -110,16 +117,33 @@ func Compile(p *shaderir.Program, version GLSLVersion) (vertexShader, fragmentSh
 				vslines = append(vslines, fmt.Sprintf("%s %s;", keyword, c.glslVarDecl(p, &t, fmt.Sprintf("V%d", i))))
 			}
 		}
-		if len(p.Funcs) > 0 {
-			vslines = append(vslines, "")
-			for _, f := range p.Funcs {
-				vslines = append(vslines, c.glslFunc(p, &f, true)...)
+
+		var funcs []*shaderir.Func
+		if p.VertexFunc.Block != nil {
+			indices := p.ReferredFuncIndicesInVertexShader()
+			sort.Ints(indices)
+			funcs = make([]*shaderir.Func, 0, len(indices))
+			for _, idx := range indices {
+				funcs = append(funcs, indexToFunc[idx])
 			}
+		} else {
+			// When a vertex entry point is not defined, allow to put all the functions. This is useful for testing.
+			funcs = make([]*shaderir.Func, 0, len(p.Funcs))
 			for _, f := range p.Funcs {
+				f := f
+				funcs = append(funcs, &f)
+			}
+		}
+		if len(funcs) > 0 {
+			vslines = append(vslines, "")
+			for _, f := range funcs {
+				vslines = append(vslines, c.glslFunc(p, f, true)...)
+			}
+			for _, f := range funcs {
 				if len(vslines) > 0 && vslines[len(vslines)-1] != "" {
 					vslines = append(vslines, "")
 				}
-				vslines = append(vslines, c.glslFunc(p, &f, false)...)
+				vslines = append(vslines, c.glslFunc(p, f, false)...)
 			}
 		}
 
@@ -156,16 +180,32 @@ func Compile(p *shaderir.Program, version GLSLVersion) (vertexShader, fragmentSh
 			fslines = append(fslines, "out vec4 fragColor;")
 		}
 
-		if len(p.Funcs) > 0 {
-			fslines = append(fslines, "")
-			for _, f := range p.Funcs {
-				fslines = append(fslines, c.glslFunc(p, &f, true)...)
+		var funcs []*shaderir.Func
+		if p.VertexFunc.Block != nil {
+			indices := p.ReferredFuncIndicesInFragmentShader()
+			sort.Ints(indices)
+			funcs = make([]*shaderir.Func, 0, len(indices))
+			for _, idx := range indices {
+				funcs = append(funcs, indexToFunc[idx])
 			}
+		} else {
+			// When a fragment entry point is not defined, allow to put all the functions. This is useful for testing.
+			funcs = make([]*shaderir.Func, 0, len(p.Funcs))
 			for _, f := range p.Funcs {
+				f := f
+				funcs = append(funcs, &f)
+			}
+		}
+		if len(funcs) > 0 {
+			fslines = append(fslines, "")
+			for _, f := range funcs {
+				fslines = append(fslines, c.glslFunc(p, f, true)...)
+			}
+			for _, f := range funcs {
 				if len(fslines) > 0 && fslines[len(fslines)-1] != "" {
 					fslines = append(fslines, "")
 				}
-				fslines = append(fslines, c.glslFunc(p, &f, false)...)
+				fslines = append(fslines, c.glslFunc(p, f, false)...)
 			}
 		}
 

internal/shaderir/program.go

@@ -347,3 +347,55 @@ func IsValidSwizzling(s string) bool {
 	}
 	return false
 }
+
+func (p *Program) ReferredFuncIndicesInVertexShader() []int {
+	return p.referredFuncIndicesInBlockEntryPoint(p.VertexFunc.Block)
+}
+
+func (p *Program) ReferredFuncIndicesInFragmentShader() []int {
+	return p.referredFuncIndicesInBlockEntryPoint(p.FragmentFunc.Block)
+}
+
+func (p *Program) referredFuncIndicesInBlockEntryPoint(b *Block) []int {
+	indexToFunc := map[int]*Func{}
+	for _, f := range p.Funcs {
+		f := f
+		indexToFunc[f.Index] = &f
+	}
+	visited := map[int]struct{}{}
+	return referredFuncIndicesInBlock(b, indexToFunc, visited)
+}
+
+func referredFuncIndicesInBlock(b *Block, indexToFunc map[int]*Func, visited map[int]struct{}) []int {
+	if b == nil {
+		return nil
+	}
+
+	var fs []int
+
+	for _, s := range b.Stmts {
+		for _, e := range s.Exprs {
+			fs = append(fs, referredFuncIndicesInExpr(&e, indexToFunc, visited)...)
+		}
+		for _, bb := range s.Blocks {
+			fs = append(fs, referredFuncIndicesInBlock(bb, indexToFunc, visited)...)
+		}
+	}
+	return fs
+}
+
+func referredFuncIndicesInExpr(e *Expr, indexToFunc map[int]*Func, visited map[int]struct{}) []int {
+	var fs []int
+
+	if e.Type == FunctionExpr {
+		if _, ok := visited[e.Index]; !ok {
+			fs = append(fs, e.Index)
+			visited[e.Index] = struct{}{}
+			fs = append(fs, referredFuncIndicesInBlock(indexToFunc[e.Index].Block, indexToFunc, visited)...)
+		}
+	}
+	for _, ee := range e.Exprs {
+		fs = append(fs, referredFuncIndicesInExpr(&ee, indexToFunc, visited)...)
+	}
+	return fs
+}

shader_test.go

@@ -1053,3 +1053,61 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 		}
 	}
 }
+
+// Issue #1701
+func TestShaderDerivatives2(t *testing.T) {
+	const w, h = 16, 16
+
+	s, err := NewShader([]byte(`package main
+
+// This function uses dfdx and then should not be in GLSL's vertex shader (#1701).
+func Foo(p vec4) vec4 {
+	return vec4(abs(dfdx(p.r)), abs(dfdy(p.g)), 0, 1)
+}
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	p := imageSrc0At(texCoord)
+	return Foo(p)
+}
+`))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	dst := NewImage(w, h)
+	src := NewImage(w, h)
+	pix := make([]byte, 4*w*h)
+	for j := 0; j < h; j++ {
+		for i := 0; i < w; i++ {
+			if i < w/2 {
+				pix[4*(j*w+i)] = 0xff
+			}
+			if j < h/2 {
+				pix[4*(j*w+i)+1] = 0xff
+			}
+			pix[4*(j*w+i)+3] = 0xff
+		}
+	}
+	src.ReplacePixels(pix)
+
+	op := &DrawRectShaderOptions{}
+	op.Images[0] = src
+	dst.DrawRectShader(w, h, s, op)
+
+	// The results of the edges might be unreliable. Skip the edges.
+	for j := 1; j < h-1; j++ {
+		for i := 1; i < w-1; i++ {
+			got := dst.At(i, j).(color.RGBA)
+			want := color.RGBA{0, 0, 0, 0xff}
+			if i == w/2-1 || i == w/2 {
+				want.R = 0xff
+			}
+			if j == h/2-1 || j == h/2 {
+				want.G = 0xff
+			}
+			if got != want {
+				t.Errorf("dst.At(%d, %d): got: %v, want: %v", i, j, got, want)
+			}
+		}
+	}
+}