internal/shader: bug fix: % operators for integer vecs didn't work

Closes #1911

internal/shader/expr.go

@@ -228,7 +228,7 @@ func (cs *compileState) parseExpr(block *block, fname string, expr ast.Expr, mar
 
 		if lhs[0].Const != nil && rhs[0].Const != nil {
 			op := e.Op
-			// https://golang.org/pkg/go/constant/#BinaryOp
+			// https://pkg.go.dev/go/constant/#BinaryOp
 			// "To force integer division of Int operands, use op == token.QUO_ASSIGN instead of
 			// token.QUO; the result is guaranteed to be Int in this case."
 			if op == token.QUO && lhs[0].Const.Kind() == gconstant.Int && rhs[0].Const.Kind() == gconstant.Int {
@@ -255,8 +255,7 @@ func (cs *compileState) parseExpr(block *block, fname string, expr ast.Expr, mar
 					v = gconstant.MakeBool(gconstant.Compare(lhs[0].Const, op, rhs[0].Const))
 				}
 				t = shaderir.Type{Main: shaderir.Bool}
-			default:
-				if op == token.REM {
+			case token.REM:
 				if !isModAvailableForConsts(&lhs[0], &rhs[0]) {
 					var wrongTypeName string
 					if lhs[0].Const.Kind() != gconstant.Int {
@@ -273,7 +272,8 @@ func (cs *compileState) parseExpr(block *block, fname string, expr ast.Expr, mar
 				if !cs.forceToInt(e, &rhs[0]) {
 					return nil, nil, nil, false
 				}
-				}
+				fallthrough
+			default:
 				v = gconstant.BinaryOp(lhs[0].Const, op, rhs[0].Const)
 				if v.Kind() == gconstant.Float {
 					t = shaderir.Type{Main: shaderir.Float}
@@ -348,6 +348,9 @@ func (cs *compileState) parseExpr(block *block, fname string, expr ast.Expr, mar
 					cs.addError(e.Pos(), fmt.Sprintf("types don't match: %s %s %s", lhst.String(), e.Op, rhst.String()))
 					return nil, nil, nil, false
 				}
+				if !cs.forceToInt(e, &rhs[0]) {
+					return nil, nil, nil, false
+				}
 			case shaderir.Int:
 				if !canTruncateToInteger(rhs[0].Const) {
 					cs.addError(e.Pos(), fmt.Sprintf("constant %s truncated to integer", rhs[0].Const.String()))

internal/shaderir/glsl/glsl.go

@@ -35,6 +35,30 @@ const (
 // utilFunctions is GLSL utility functions for old GLSL versions.
 const utilFunctions = `int modInt(int x, int y) {
 	return x - y*(x/y);
+}
+
+ivec2 modInt(ivec2 x, int y) {
+	return x - y*(x/y);
+}
+
+ivec3 modInt(ivec3 x, int y) {
+	return x - y*(x/y);
+}
+
+ivec4 modInt(ivec4 x, int y) {
+	return x - y*(x/y);
+}
+
+ivec2 modInt(ivec2 x, ivec2 y) {
+	return x - y*(x/y);
+}
+
+ivec3 modInt(ivec3 x, ivec3 y) {
+	return x - y*(x/y);
+}
+
+ivec4 modInt(ivec4 x, ivec4 y) {
+	return x - y*(x/y);
 }`
 
 func VertexPrelude(version GLSLVersion) string {

shader_test.go

@@ -15,6 +15,7 @@
 package ebiten_test
 
 import (
+	"fmt"
 	"image"
 	"image/color"
 	"math"
@@ -1503,3 +1504,65 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
 }
+
+func TestShaderIVecMod(t *testing.T) {
+	cases := []struct {
+		source string
+		want   color.RGBA
+	}{
+		{
+			source: `a := ivec4(0x24, 0x3f, 0x6a, 0x88)
+return vec4(a)/255`,
+			want: color.RGBA{0x24, 0x3f, 0x6a, 0x88},
+		},
+		{
+			source: `a := ivec4(0x24, 0x3f, 0x6a, 0x88)
+a %= 0x85
+return vec4(a)/255`,
+			want: color.RGBA{0x24, 0x3f, 0x6a, 0x03},
+		},
+		{
+			source: `a := ivec4(0x24, 0x3f, 0x6a, 0x88)
+a %= ivec4(0x85, 0xa3, 0x08, 0xd3)
+return vec4(a)/255`,
+			want: color.RGBA{0x24, 0x3f, 0x02, 0x88},
+		},
+		{
+			source: `a := ivec4(0x24, 0x3f, 0x6a, 0x88)
+b := a % 0x85
+return vec4(b)/255`,
+			want: color.RGBA{0x24, 0x3f, 0x6a, 0x03},
+		},
+		{
+			source: `a := ivec4(0x24, 0x3f, 0x6a, 0x88)
+b := a % ivec4(0x85, 0xa3, 0x08, 0xd3)
+return vec4(b)/255`,
+			want: color.RGBA{0x24, 0x3f, 0x02, 0x88},
+		},
+	}
+
+	for _, tc := range cases {
+		shader := fmt.Sprintf(`package main
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	%s
+}
+`, tc.source)
+		const w, h = 1, 1
+
+		dst := ebiten.NewImage(w, h)
+		defer dst.Dispose()
+
+		s, err := ebiten.NewShader([]byte(shader))
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer s.Dispose()
+
+		op := &ebiten.DrawRectShaderOptions{}
+		dst.DrawRectShader(w, h, s, op)
+		if got, want := dst.At(0, 0).(color.RGBA), tc.want; !sameColors(got, want, 1) {
+			t.Errorf("%s: got: %v, want: %v", tc.source, got, want)
+		}
+	}
+}