shaderir: Add swizzling

internal/shaderir/glsl.go

@@ -19,6 +19,40 @@ import (
 	"strings"
 )
 
+func isValidSwizzling(s string) bool {
+	if len(s) < 1 || 4 < len(s) {
+		return false
+	}
+
+	const (
+		xyzw = "xyzw"
+		rgba = "rgba"
+		strq = "strq"
+	)
+
+	switch {
+	case strings.IndexByte(xyzw, s[0]) >= 0:
+		for _, c := range s {
+			if strings.IndexRune(xyzw, c) == -1 {
+				return false
+			}
+		}
+	case strings.IndexByte(rgba, s[0]) >= 0:
+		for _, c := range s {
+			if strings.IndexRune(rgba, c) == -1 {
+				return false
+			}
+		}
+	case strings.IndexByte(strq, s[0]) >= 0:
+		for _, c := range s {
+			if strings.IndexRune(strq, c) == -1 {
+				return false
+			}
+		}
+	}
+	return false
+}
+
 func (p *Program) structName(t *Type) string {
 	if t.Main != Struct {
 		panic("shaderir: the given type at structName must be a struct")
@@ -190,6 +224,11 @@ func (p *Program) glslBlock(b *Block, level int, localVarIndex int) []string {
 			}
 		case BuiltinFuncExpr:
 			return string(e.BuiltinFunc)
+		case SwizzlingExpr:
+			if isValidSwizzling(e.Swizzling) {
+				return fmt.Sprintf("?(unexpected swizzling: %s)", e.Swizzling)
+			}
+			return e.Swizzling
 		case Ident:
 			return e.Ident
 		case Unary:

internal/shaderir/ir_test.go

@@ -98,6 +98,13 @@ func builtinFuncExpr(f BuiltinFunc) Expr {
 	}
 }
 
+func swizzlingExpr(swizzling string) Expr {
+	return Expr{
+		Type:      SwizzlingExpr,
+		Swizzling: swizzling,
+	}
+}
+
 func identExpr(ident string) Expr {
 	return Expr{
 		Type:  Ident,
@@ -455,7 +462,7 @@ varying vec3 V0;`,
 							{Main: Vec4},
 						},
 						OutParams: []Type{
-							{Main: Float},
+							{Main: Vec2},
 						},
 						Block: block(
 							nil,
@@ -463,15 +470,15 @@ varying vec3 V0;`,
 								varNameExpr(Local, 1),
 								fieldSelectorExpr(
 									varNameExpr(Local, 0),
-									identExpr("x"),
+									swizzlingExpr("xz"),
 								),
 							),
 						),
 					},
 				},
 			},
-			Glsl: `void F0(in vec4 l0, out float l1) {
-	l1 = (l0).x;
+			Glsl: `void F0(in vec4 l0, out vec2 l1) {
+	l1 = (l0).xz;
 }`,
 		},
 		{

internal/shaderir/program.go

@@ -89,6 +89,7 @@ type Expr struct {
 	Int         int32
 	Float       float32
 	BuiltinFunc BuiltinFunc
+	Swizzling   string
 	Ident       string
 	Op          Op
 }
@@ -100,6 +101,7 @@ const (
 	FloatExpr
 	VarName
 	BuiltinFuncExpr
+	SwizzlingExpr
 	Ident
 	Unary
 	Binary