ebiten: bug fix: add an indirect function call for a fragment shader

Closes #2245
Closes #2247

internal/shader/testdata/for5.expected.fs

@@ -3,27 +3,34 @@ uniform float U1;
 uniform float U2;
 
 int F0(in int l0);
+void F1(in vec4 l0, out vec4 l1);
 
 int F0(in int l0) {
 	return l0;
 }
 
-void main(void) {
+void F1(in vec4 l0, out vec4 l1) {
-	int l0 = 0;
 	int l2 = 0;
-	l0 = 0;
+	int l4 = 0;
-	for (int l1 = 0; l1 < 10; l1++) {
+	l2 = 0;
-		int l2 = 0;
+	for (int l3 = 0; l3 < 10; l3++) {
-		l2 = F0(l1);
+		int l4 = 0;
-		l0 = (l0) + (l2);
+		l4 = F0(l3);
-		for (int l3 = 0; l3 < 10; l3++) {
+		l2 = (l2) + (l4);
-			int l4 = 0;
+		for (int l5 = 0; l5 < 10; l5++) {
-			l4 = F0(l3);
+			int l6 = 0;
-			l0 = (l0) + (l4);
+			l6 = F0(l5);
+			l2 = (l2) + (l6);
 		}
 	}
-	l2 = 0;
+	l4 = 0;
-	l0 = (l0) + (l2);
+	l2 = (l2) + (l4);
-	gl_FragColor = vec4(l0);
+	l1 = vec4(l2);
 	return;
 }
+
+void main(void) {
+	vec4 l0 = vec4(0);
+	F1(gl_FragCoord, l0);
+	gl_FragColor = l0;
+}

internal/shader/testdata/issue1238.expected.fs

@@ -1,8 +1,16 @@
-void main(void) {
+void F0(in vec4 l0, out vec4 l1);
+
+void F0(in vec4 l0, out vec4 l1) {
 	if (true) {
-		gl_FragColor = gl_FragCoord;
+		l1 = l0;
 		return;
 	}
-	gl_FragColor = gl_FragCoord;
+	l1 = l0;
 	return;
 }
+
+void main(void) {
+	vec4 l0 = vec4(0);
+	F0(gl_FragCoord, l0);
+	gl_FragColor = l0;
+}

internal/shader/testdata/issue1245.expected.fs

@@ -1,8 +1,16 @@
-void main(void) {
+void F0(in vec4 l0, out vec4 l1);
-	vec4 l0 = vec4(0);
+
-	for (float l1 = 0.0; l1 < 4.0; l1++) {
+void F0(in vec4 l0, out vec4 l1) {
-		(l0).x = ((l0).x) + ((l1) * (1.0000000000e-02));
+	vec4 l2 = vec4(0);
+	for (float l3 = 0.0; l3 < 4.0; l3++) {
+		(l2).x = ((l2).x) + ((l3) * (1.0000000000e-02));
 	}
-	gl_FragColor = l0;
+	l1 = l2;
 	return;
 }
+
+void main(void) {
+	vec4 l0 = vec4(0);
+	F0(gl_FragCoord, l0);
+	gl_FragColor = l0;
+}

internal/shader/testdata/issue1701.expected.fs

@@ -1,5 +1,6 @@
 void F2(void);
 void F3(void);
+void F5(in vec4 l0, out vec4 l1);
 
 void F2(void) {
 }
@@ -8,8 +9,14 @@ void F3(void) {
 	F2();
 }
 
-void main(void) {
+void F5(in vec4 l0, out vec4 l1) {
 	F3();
-	gl_FragColor = vec4(0.0);
+	l1 = vec4(0.0);
 	return;
 }
+
+void main(void) {
+	vec4 l0 = vec4(0);
+	F5(gl_FragCoord, l0);
+	gl_FragColor = l0;
+}

internal/shader/testdata/vertex_fragment.expected.fs

@@ -2,7 +2,15 @@ uniform vec2 U0;
 varying vec2 V0;
 varying vec4 V1;
 
-void main(void) {
+void F0(in vec4 l0, in vec2 l1, in vec4 l2, out vec4 l3);
-	gl_FragColor = vec4((gl_FragCoord).x, (V0).y, (V1).z, 1.0);
+
+void F0(in vec4 l0, in vec2 l1, in vec4 l2, out vec4 l3) {
+	l3 = vec4((l0).x, (l1).y, (l2).z, 1.0);
 	return;
 }
+
+void main(void) {
+	vec4 l0 = vec4(0);
+	F0(gl_FragCoord, V0, V1, l0);
+	gl_FragColor = l0;
+}

internal/shaderir/glsl/glsl.go

@@ -92,6 +92,8 @@ func (c *compileContext) structName(p *shaderir.Program, t *shaderir.Type) strin
 }
 
 func Compile(p *shaderir.Program, version GLSLVersion) (vertexShader, fragmentShader string) {
+	p = adjustProgram(p)
+
 	c := &compileContext{
 		version:     version,
 		structNames: map[string]string{},
@@ -625,3 +627,109 @@ func (c *compileContext) block(p *shaderir.Program, topBlock, block *shaderir.Bl
 
 	return lines
 }
+
+func adjustProgram(p *shaderir.Program) *shaderir.Program {
+	if p.FragmentFunc.Block == nil {
+		return p
+	}
+
+	// Shallow-clone the program in order not to modify p itself.
+	newP := *p
+
+	// Create a new slice not to affect the original p.
+	newP.Funcs = make([]shaderir.Func, len(p.Funcs))
+	copy(newP.Funcs, p.Funcs)
+
+	// Create a new function whose body is the same is the fragment shader's entry point.
+	// The entry point will call this.
+	// This indirect call is needed for these issues:
+	// - Assignment to gl_FragColor doesn't work (#2245)
+	// - There are some odd compilers that don't work with early returns and gl_FragColor (#2247)
+
+	// Determine a unique index of the new function.
+	var funcIdx int
+	for _, f := range newP.Funcs {
+		if funcIdx <= f.Index {
+			funcIdx = f.Index + 1
+		}
+	}
+
+	// For parameters of a fragment func, see the comment in internal/shaderir/program.go.
+	inParams := make([]shaderir.Type, 1+len(newP.Varyings))
+	inParams[0] = shaderir.Type{
+		Main: shaderir.Vec4, // gl_FragCoord
+	}
+	copy(inParams[1:], newP.Varyings)
+
+	outParams := make([]shaderir.Type, 1)
+	outParams[0] = shaderir.Type{
+		Main: shaderir.Vec4, // gl_FragColor
+	}
+
+	newP.Funcs = append(newP.Funcs, shaderir.Func{
+		Index:     funcIdx,
+		InParams:  inParams,
+		OutParams: outParams,
+		Return:    shaderir.Type{},
+		Block:     newP.FragmentFunc.Block,
+	})
+
+	// Create an AST to call the new function.
+	call := []shaderir.Expr{
+		{
+			Type:  shaderir.FunctionExpr,
+			Index: funcIdx,
+		},
+	}
+	for i := 0; i < 1+len(newP.Varyings); i++ {
+		call = append(call, shaderir.Expr{
+			Type:  shaderir.LocalVariable,
+			Index: i,
+		})
+	}
+	call = append(call, shaderir.Expr{
+		Type:  shaderir.LocalVariable,
+		Index: 1 + len(newP.Varyings) + 1, // l0 as an out parameter.
+	})
+
+	// Replace the entry point with just calling the new function.
+	stmts := []shaderir.Stmt{
+		{
+			Type: shaderir.ExprStmt,
+			Exprs: []shaderir.Expr{
+				{
+					Type:  shaderir.Call,
+					Exprs: call,
+				},
+			},
+		},
+		{
+			Type: shaderir.Assign,
+			Exprs: []shaderir.Expr{
+				// gl_FragColor
+				{
+					Type:  shaderir.LocalVariable,
+					Index: 1 + len(newP.Varyings),
+				},
+				// l0
+				{
+					Type:  shaderir.LocalVariable,
+					Index: 1 + len(newP.Varyings) + 1,
+				},
+			},
+		},
+	}
+	newP.FragmentFunc = shaderir.FragmentFunc{
+		Block: &shaderir.Block{
+			LocalVars: []shaderir.Type{
+				{
+					Main: shaderir.Vec4,
+				},
+			},
+			LocalVarIndexOffset: 1 + len(newP.Varyings) + 1,
+			Stmts:               stmts,
+		},
+	}
+
+	return &newP
+}

internal/shaderir/ir_test.go

@@ -1019,12 +1019,20 @@ uniform float U0;
 varying float V0;
 varying vec2 V1;
 
+void F0(in vec4 l0, in float l1, in vec2 l2, out vec4 l3);
+
+void F0(in vec4 l0, in float l1, in vec2 l2, out vec4 l3) {
+	float l4 = float(0);
+	vec2 l5 = vec2(0);
+	l3 = l0;
+	l4 = l1;
+	l5 = l2;
+}
+
 void main(void) {
-	float l0 = float(0);
+	vec4 l0 = vec4(0);
-	vec2 l1 = vec2(0);
+	F0(gl_FragCoord, V0, V1, l0);
-	gl_FragColor = gl_FragCoord;
+	gl_FragColor = l0;
-	l0 = V0;
-	l1 = V1;
 }`,
 		},
 	}

shader_test.go

@@ -1181,3 +1181,58 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 		}
 	}
 }
+
+// Issue #2245, #2247
+func TestShaderDrawRect(t *testing.T) {
+	const (
+		dstW = 16
+		dstH = 16
+		srcW = 8
+		srcH = 8
+	)
+
+	dst := ebiten.NewImage(dstW, dstH)
+	src := ebiten.NewImage(srcW, srcH)
+
+	s, err := ebiten.NewShader([]byte(`package main
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	// Adjust texCoord into [0, 1].
+	origin, size := imageSrcRegionOnTexture()
+	texCoord -= origin
+	texCoord /= size
+	if texCoord.x >= 0.5 && texCoord.y >= 0.5 {
+		return vec4(1, 0, 0, 1)
+	}
+	return vec4(0, 1, 0, 1)
+}
+`))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	const (
+		offsetX = (dstW - srcW) / 2
+		offsetY = (dstH - srcH) / 2
+	)
+	op := &ebiten.DrawRectShaderOptions{}
+	op.GeoM.Translate(offsetX, offsetY)
+	op.Images[0] = src
+	dst.DrawRectShader(srcW, srcH, s, op)
+	for j := 0; j < dstH; j++ {
+		for i := 0; i < dstW; i++ {
+			got := dst.At(i, j).(color.RGBA)
+			var want color.RGBA
+			if offsetX <= i && i < offsetX+srcW && offsetY <= j && j < offsetY+srcH {
+				if offsetX+srcW/2 <= i && offsetY+srcH/2 <= j {
+					want = color.RGBA{0xff, 0, 0, 0xff}
+				} else {
+					want = color.RGBA{0, 0xff, 0, 0xff}
+				}
+			}
+			if got != want {
+				t.Errorf("dst.At(%d, %d): got: %v, want: %v", i, j, got, want)
+			}
+		}
+	}
+}