internal/shader: bug fix: ++/-- statements didn't work for vec2 on browsers

Closes #2933

internal/shader/stmt.go

@@ -292,7 +292,7 @@ func (cs *compileState) parseStmt(block *block, fname string, stmt ast.Stmt, inP
 		})
 
 	case *ast.IncDecStmt:
-		exprs, _, ss, ok := cs.parseExpr(block, fname, stmt.X, true)
+		exprs, ts, ss, ok := cs.parseExpr(block, fname, stmt.X, true)
 		if !ok {
 			return nil, false
 		}
@@ -304,6 +304,16 @@ func (cs *compileState) parseStmt(block *block, fname string, stmt ast.Stmt, inP
 		case token.DEC:
 			op = shaderir.Sub
 		}
+		var c gconstant.Value
+		switch {
+		case ts[0].Main == shaderir.Int, ts[0].IsIntVector():
+			c = gconstant.MakeInt64(1)
+		case ts[0].Main == shaderir.Float, ts[0].IsFloatVector():
+			c = gconstant.MakeFloat64(1)
+		default:
+			cs.addError(stmt.Pos(), fmt.Sprintf("invalid operation %s (non-numeric type %s)", stmt.Tok.String(), ts[0].String()))
+			return nil, false
+		}
 		stmts = append(stmts, shaderir.Stmt{
 			Type: shaderir.Assign,
 			Exprs: []shaderir.Expr{
@@ -315,7 +325,7 @@ func (cs *compileState) parseStmt(block *block, fname string, stmt ast.Stmt, inP
 						exprs[0],
 						{
 							Type:  shaderir.NumberExpr,
-							Const: gconstant.MakeInt64(1),
+							Const: c,
 						},
 					},
 				},

shader_test.go

@@ -2487,3 +2487,75 @@ func Fragment(dstPos vec4, srcPos vec2, color vec4) vec4 {
 		}
 	}
 }
+
+// Issue #2933
+func TestShaderIncDecStmt(t *testing.T) {
+	const w, h = 16, 16
+
+	dst := ebiten.NewImage(w, h)
+	s, err := ebiten.NewShader([]byte(`//kage:unit pixels
+
+package main
+
+func Fragment(dstPos vec4, srcPos vec2, color vec4) vec4 {
+	a := 0
+	a++
+	b := -0.5
+	b++
+	c := ivec2(0)
+	c++
+	d := vec2(-0.25)
+	d++
+	return vec4(float(a), b, float(c.x), d.y)
+}
+`))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	dst.DrawRectShader(w, h, s, nil)
+
+	for j := 0; j < h; j++ {
+		for i := 0; i < w; i++ {
+			got := dst.At(i, j).(color.RGBA)
+			want := color.RGBA{R: 0xff, G: 0x80, B: 0xff, A: 0xc0}
+			if !sameColors(got, want, 2) {
+				t.Errorf("dst.At(%d, %d): got: %v, want: %v", i, j, got, want)
+			}
+		}
+	}
+
+	dst.Clear()
+
+	s, err = ebiten.NewShader([]byte(`//kage:unit pixels
+
+package main
+
+func Fragment(dstPos vec4, srcPos vec2, color vec4) vec4 {
+	a := 1
+	a--
+	b := 1.5
+	b--
+	c := ivec2(1)
+	c--
+	d := vec2(1.25)
+	d--
+	return vec4(float(a), b, float(c.x), d.y)
+}
+`))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	dst.DrawRectShader(w, h, s, nil)
+
+	for j := 0; j < h; j++ {
+		for i := 0; i < w; i++ {
+			got := dst.At(i, j).(color.RGBA)
+			want := color.RGBA{R: 0x00, G: 0x80, B: 0x00, A: 0x40}
+			if !sameColors(got, want, 2) {
+				t.Errorf("dst.At(%d, %d): got: %v, want: %v", i, j, got, want)
+			}
+		}
+	}
+}