From 0415773b940719905b0d3242d38799a2773d4b6e Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Fri, 21 Jan 2022 01:59:54 +0900
Subject: [PATCH] internal/shader: bug fix: allow the *= operator for a vector
 and a matrix

Updates #1971
---
 internal/shader/stmt.go |  7 ++++++
 shader_test.go          | 54 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+)

diff --git a/internal/shader/stmt.go b/internal/shader/stmt.go
index 76b18a0be..2199a32c0 100644
--- a/internal/shader/stmt.go
+++ b/internal/shader/stmt.go
@@ -111,6 +111,13 @@ func (cs *compileState) parseStmt(block *block, fname string, stmt ast.Stmt, inP
 				case shaderir.Vec2, shaderir.Vec3, shaderir.Vec4, shaderir.Mat2, shaderir.Mat3, shaderir.Mat4:
 					if rts[0].Main == shaderir.Float {
 						// OK
+					} else if op == shaderir.Mul && ((lts[0].Main == shaderir.Vec2 && rts[0].Main == shaderir.Mat2) ||
+						(lts[0].Main == shaderir.Vec3 && rts[0].Main == shaderir.Mat3) ||
+						(lts[0].Main == shaderir.Vec4 && rts[0].Main == shaderir.Mat4) ||
+						(lts[0].Main == shaderir.Mat2 && rts[0].Main == shaderir.Vec2) ||
+						(lts[0].Main == shaderir.Mat3 && rts[0].Main == shaderir.Vec3) ||
+						(lts[0].Main == shaderir.Mat4 && rts[0].Main == shaderir.Vec4)) {
+						// OK
 					} else if rhs[0].Const != nil && rhs[0].Const.Kind() == gconstant.Int {
 						rhs[0].Const = gconstant.ToFloat(rhs[0].Const)
 						rhs[0].ConstType = shaderir.ConstTypeFloat
diff --git a/shader_test.go b/shader_test.go
index 41a889d0b..0bea61f78 100644
--- a/shader_test.go
+++ b/shader_test.go
@@ -1600,3 +1600,57 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 		}
 	}
 }
+
+// Issue #1971
+func TestShaderOperatorMultiplyAssign(t *testing.T) {
+	cases := []struct {
+		stmt string
+		err  bool
+	}{
+		{stmt: "a := 1.0; a *= 2", err: false},
+		{stmt: "a := 1.0; a *= 2.0", err: false},
+		{stmt: "a := 1.0; a *= int(2)", err: true},
+		{stmt: "a := 1.0; a *= vec2(2)", err: true},
+		{stmt: "a := 1.0; a *= vec3(2)", err: true},
+		{stmt: "a := 1.0; a *= vec4(2)", err: true},
+		{stmt: "a := 1.0; a *= mat2(2)", err: true},
+		{stmt: "a := 1.0; a *= mat3(2)", err: true},
+		{stmt: "a := 1.0; a *= mat4(2)", err: true},
+		{stmt: "a := vec2(1); a *= 2", err: false},
+		{stmt: "a := vec2(1); a *= 2.0", err: false},
+		{stmt: "a := vec2(1); a *= int(2)", err: true},
+		{stmt: "a := vec2(1); a *= vec2(2)", err: false},
+		{stmt: "a := vec2(1); a += vec2(2)", err: false},
+		{stmt: "a := vec2(1); a *= vec3(2)", err: true},
+		{stmt: "a := vec2(1); a *= vec4(2)", err: true},
+		{stmt: "a := vec2(1); a *= mat2(2)", err: false},
+		{stmt: "a := vec2(1); a += mat2(2)", err: true},
+		{stmt: "a := vec2(1); a *= mat3(2)", err: true},
+		{stmt: "a := vec2(1); a *= mat4(2)", err: true},
+		{stmt: "a := mat2(1); a *= 2", err: false},
+		{stmt: "a := mat2(1); a *= 2.0", err: false},
+		{stmt: "a := mat2(1); a *= int(2)", err: true},
+		{stmt: "a := mat2(1); a *= vec2(2)", err: false},
+		{stmt: "a := mat2(1); a += vec2(2)", err: true},
+		{stmt: "a := mat2(1); a *= vec3(2)", err: true},
+		{stmt: "a := mat2(1); a *= vec4(2)", err: true},
+		{stmt: "a := mat2(1); a *= mat2(2)", err: false},
+		{stmt: "a := mat2(1); a += mat2(2)", err: false},
+		{stmt: "a := mat2(1); a *= mat3(2)", err: true},
+		{stmt: "a := mat2(1); a *= mat4(2)", err: true},
+	}
+
+	for _, c := range cases {
+		_, err := ebiten.NewShader([]byte(fmt.Sprintf(`package main
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	%s
+	return position
+}`, c.stmt)))
+		if err == nil && c.err {
+			t.Errorf("%s must return an error but does not", c.stmt)
+		} else if err != nil && !c.err {
+			t.Errorf("%s must not return nil but returned %v", c.stmt, err)
+		}
+	}
+}