shader: Enable to put global variables anywhere

internal/shader/shader.go

@@ -140,8 +140,16 @@ func (s *compileState) addError(pos token.Pos, str string) {
 }
 
 func (cs *compileState) parse(f *ast.File) {
+	// Parse GenDecl for global variables, and then parse functions.
 	for _, d := range f.Decls {
-		cs.parseDecl(&cs.global, d)
+		if _, ok := d.(*ast.FuncDecl); !ok {
+			cs.parseDecl(&cs.global, d)
+		}
+	}
+	for _, d := range f.Decls {
+		if _, ok := d.(*ast.FuncDecl); ok {
+			cs.parseDecl(&cs.global, d)
+		}
 	}
 
 	if len(cs.errs) > 0 {

internal/shader/shader_test.go

@@ -135,8 +135,6 @@ func Foo(foo vec2) vec4 {
 			Name: "vertex",
 			Src: `package main
 
-var ScreenSize vec2
-
 func Vertex(position vec2, texCoord vec2, color vec4) (position vec4, texCoord vec2, color vec4) {
 	projectionMatrix := mat4(
 		2 / ScreenSize.x, 0, 0, 0,
@@ -145,7 +143,9 @@ func Vertex(position vec2, texCoord vec2, color vec4) (position vec4, texCoord v
 		-1, -1, 0, 1,
 	)
 	return projectionMatrix * vec4(position, 0, 1), texCoord, color
-}`,
+}
+
+var ScreenSize vec2`,
 			VS: `uniform vec2 U0;
 attribute vec2 A0;
 attribute vec2 A1;
@@ -161,6 +161,9 @@ void main(void) {
 	V1 = A2;
 	return;
 }`,
+			FS: `uniform vec2 U0;
+varying vec2 V0;
+varying vec4 V1;`,
 		},
 	}
 	for _, tc := range tests {