ebiten: Bug fix: Stencil buffers should not be cleared until all the vertices are rendered

Updates #1684

image_test.go

@@ -2240,3 +2240,130 @@ func TestImageSubImageFill(t *testing.T) {
 		}
 	}
 }
+
+func TestImageEvenOdd(t *testing.T) {
+	emptyImage := NewImage(3, 3)
+	emptyImage.Fill(color.White)
+	emptySubImage := emptyImage.SubImage(image.Rect(1, 1, 2, 2)).(*Image)
+
+	vs0 := []Vertex{
+		{
+			DstX: 1, DstY: 1, SrcX: 1, SrcY: 1,
+			ColorR: 1, ColorG: 0, ColorB: 0, ColorA: 1,
+		},
+		{
+			DstX: 15, DstY: 1, SrcX: 1, SrcY: 1,
+			ColorR: 1, ColorG: 0, ColorB: 0, ColorA: 1,
+		},
+		{
+			DstX: 1, DstY: 15, SrcX: 1, SrcY: 1,
+			ColorR: 1, ColorG: 0, ColorB: 0, ColorA: 1,
+		},
+		{
+			DstX: 15, DstY: 15, SrcX: 1, SrcY: 1,
+			ColorR: 1, ColorG: 0, ColorB: 0, ColorA: 1,
+		},
+	}
+	is0 := []uint16{0, 1, 2, 1, 2, 3}
+
+	vs1 := []Vertex{
+		{
+			DstX: 2, DstY: 2, SrcX: 1, SrcY: 1,
+			ColorR: 0, ColorG: 1, ColorB: 0, ColorA: 1,
+		},
+		{
+			DstX: 14, DstY: 2, SrcX: 1, SrcY: 1,
+			ColorR: 0, ColorG: 1, ColorB: 0, ColorA: 1,
+		},
+		{
+			DstX: 2, DstY: 14, SrcX: 1, SrcY: 1,
+			ColorR: 0, ColorG: 1, ColorB: 0, ColorA: 1,
+		},
+		{
+			DstX: 14, DstY: 14, SrcX: 1, SrcY: 1,
+			ColorR: 0, ColorG: 1, ColorB: 0, ColorA: 1,
+		},
+	}
+	is1 := []uint16{4, 5, 6, 5, 6, 7}
+
+	vs2 := []Vertex{
+		{
+			DstX: 3, DstY: 3, SrcX: 1, SrcY: 1,
+			ColorR: 0, ColorG: 0, ColorB: 1, ColorA: 1,
+		},
+		{
+			DstX: 13, DstY: 3, SrcX: 1, SrcY: 1,
+			ColorR: 0, ColorG: 0, ColorB: 1, ColorA: 1,
+		},
+		{
+			DstX: 3, DstY: 13, SrcX: 1, SrcY: 1,
+			ColorR: 0, ColorG: 0, ColorB: 1, ColorA: 1,
+		},
+		{
+			DstX: 13, DstY: 13, SrcX: 1, SrcY: 1,
+			ColorR: 0, ColorG: 0, ColorB: 1, ColorA: 1,
+		},
+	}
+	is2 := []uint16{8, 9, 10, 9, 10, 11}
+
+	// Draw all the vertices once. The even-odd rule is applied for all the vertices once.
+	dst := NewImage(16, 16)
+	op := &DrawTrianglesOptions{
+		EvenOdd: true,
+	}
+	dst.DrawTriangles(append(append(vs0, vs1...), vs2...), append(append(is0, is1...), is2...), emptySubImage, op)
+	for j := 0; j < 16; j++ {
+		for i := 0; i < 16; i++ {
+			got := dst.At(i, j)
+			var want color.RGBA
+			switch {
+			case 3 <= i && i < 13 && 3 <= j && j < 13:
+				want = color.RGBA{0, 0, 0xff, 0xff}
+			case 2 <= i && i < 14 && 2 <= j && j < 14:
+				want = color.RGBA{0, 0, 0, 0}
+			case 1 <= i && i < 15 && 1 <= j && j < 15:
+				want = color.RGBA{0xff, 0, 0, 0xff}
+			default:
+				want = color.RGBA{0, 0, 0, 0}
+			}
+			if got != want {
+				t.Errorf("dst.At(%d, %d): got: %v, want: %v", i, j, got, want)
+			}
+		}
+	}
+
+	// Do the same thing with a little shift. This confirms that the underlying stencil buffer is cleared correctly.
+	for i := range vs0 {
+		vs0[i].DstX++
+		vs0[i].DstY++
+	}
+	for i := range vs1 {
+		vs1[i].DstX++
+		vs1[i].DstY++
+	}
+	for i := range vs2 {
+		vs2[i].DstX++
+		vs2[i].DstY++
+	}
+	dst.Clear()
+	dst.DrawTriangles(append(append(vs0, vs1...), vs2...), append(append(is0, is1...), is2...), emptySubImage, op)
+	for j := 0; j < 16; j++ {
+		for i := 0; i < 16; i++ {
+			got := dst.At(i, j)
+			var want color.RGBA
+			switch {
+			case 4 <= i && i < 14 && 4 <= j && j < 14:
+				want = color.RGBA{0, 0, 0xff, 0xff}
+			case 3 <= i && i < 15 && 3 <= j && j < 15:
+				want = color.RGBA{0, 0, 0, 0}
+			case 2 <= i && i < 16 && 2 <= j && j < 16:
+				want = color.RGBA{0xff, 0, 0, 0xff}
+			default:
+				want = color.RGBA{0, 0, 0, 0}
+			}
+			if got != want {
+				t.Errorf("dst.At(%d, %d): got: %v, want: %v", i, j, got, want)
+			}
+		}
+	}
+}

internal/graphicsdriver/metal/graphics.go

@@ -745,15 +745,15 @@ func (g *Graphics) draw(rps mtl.RenderPipelineState, dst *Image, dstRegion drive
 	case drawWithStencil:
 		desc := mtl.DepthStencilDescriptor{
 			BackFaceStencil: mtl.StencilDescriptor{
-				StencilFailureOperation:   mtl.StencilOperationZero,
+				StencilFailureOperation:   mtl.StencilOperationKeep,
-				DepthFailureOperation:     mtl.StencilOperationZero,
+				DepthFailureOperation:     mtl.StencilOperationKeep,
-				DepthStencilPassOperation: mtl.StencilOperationZero,
+				DepthStencilPassOperation: mtl.StencilOperationKeep,
 				StencilCompareFunction:    mtl.CompareFunctionNotEqual,
 			},
 			FrontFaceStencil: mtl.StencilDescriptor{
-				StencilFailureOperation:   mtl.StencilOperationZero,
+				StencilFailureOperation:   mtl.StencilOperationKeep,
-				DepthFailureOperation:     mtl.StencilOperationZero,
+				DepthFailureOperation:     mtl.StencilOperationKeep,
-				DepthStencilPassOperation: mtl.StencilOperationZero,
+				DepthStencilPassOperation: mtl.StencilOperationKeep,
 				StencilCompareFunction:    mtl.CompareFunctionNotEqual,
 			},
 		}

internal/graphicsdriver/opengl/context_desktop.go

@@ -264,7 +264,6 @@ func (c *context) bindStencilBuffer(f framebufferNative, r renderbufferNative) e
 	if s := gl.CheckFramebufferStatusEXT(gl.FRAMEBUFFER); s != gl.FRAMEBUFFER_COMPLETE {
 		return errors.New(fmt.Sprintf("opengl: glFramebufferRenderbuffer failed: %d", s))
 	}
-	gl.Clear(gl.STENCIL_BUFFER_BIT)
 	return nil
 }
 
@@ -550,6 +549,7 @@ func (c *context) disableStencilTest() {
 }
 
 func (c *context) beginStencilWithEvenOddRule() {
+	gl.Clear(gl.STENCIL_BUFFER_BIT)
 	gl.StencilFunc(gl.ALWAYS, 0x00, 0xff)
 	gl.StencilOp(gl.KEEP, gl.KEEP, gl.INVERT)
 	gl.ColorMask(false, false, false, false)
@@ -557,6 +557,6 @@ func (c *context) beginStencilWithEvenOddRule() {
 
 func (c *context) endStencilWithEvenOddRule() {
 	gl.StencilFunc(gl.NOTEQUAL, 0x00, 0xff)
-	gl.StencilOp(gl.ZERO, gl.ZERO, gl.ZERO)
+	gl.StencilOp(gl.KEEP, gl.KEEP, gl.KEEP)
 	gl.ColorMask(true, true, true, true)
 }

internal/graphicsdriver/opengl/context_js.go

@@ -298,7 +298,6 @@ func (c *context) bindStencilBuffer(f framebufferNative, r renderbufferNative) e
 	if s := gl.checkFramebufferStatus.Invoke(gles.FRAMEBUFFER); s.Int() != gles.FRAMEBUFFER_COMPLETE {
 		return errors.New(fmt.Sprintf("opengl: framebufferRenderbuffer failed: %d", s.Int()))
 	}
-	gl.clear.Invoke(gles.STENCIL_BUFFER_BIT)
 	return nil
 }
 
@@ -660,6 +659,7 @@ func (c *context) disableStencilTest() {
 
 func (c *context) beginStencilWithEvenOddRule() {
 	gl := c.gl
+	gl.clear.Invoke(gles.STENCIL_BUFFER_BIT)
 	gl.stencilFunc.Invoke(gles.ALWAYS, 0x00, 0xff)
 	gl.stencilOp.Invoke(gles.KEEP, gles.KEEP, gles.INVERT)
 	gl.colorMask.Invoke(false, false, false, false)
@@ -668,6 +668,6 @@ func (c *context) beginStencilWithEvenOddRule() {
 func (c *context) endStencilWithEvenOddRule() {
 	gl := c.gl
 	gl.stencilFunc.Invoke(gles.NOTEQUAL, 0x00, 0xff)
-	gl.stencilOp.Invoke(gles.ZERO, gles.ZERO, gles.ZERO)
+	gl.stencilOp.Invoke(gles.KEEP, gles.KEEP, gles.KEEP)
 	gl.colorMask.Invoke(true, true, true, true)
 }

internal/graphicsdriver/opengl/context_mobile.go

@@ -246,7 +246,6 @@ func (c *context) bindStencilBuffer(f framebufferNative, r renderbufferNative) e
 	if s := c.ctx.CheckFramebufferStatus(gles.FRAMEBUFFER); s != gles.FRAMEBUFFER_COMPLETE {
 		return errors.New(fmt.Sprintf("opengl: glFramebufferRenderbuffer failed: %d", s))
 	}
-	c.ctx.Clear(gles.STENCIL_BUFFER_BIT)
 	return nil
 }
 
@@ -511,6 +510,7 @@ func (c *context) disableStencilTest() {
 }
 
 func (c *context) beginStencilWithEvenOddRule() {
+	c.ctx.Clear(gles.STENCIL_BUFFER_BIT)
 	c.ctx.StencilFunc(gles.ALWAYS, 0x00, 0xff)
 	c.ctx.StencilOp(gles.KEEP, gles.KEEP, gles.INVERT)
 	c.ctx.ColorMask(false, false, false, false)
@@ -518,6 +518,6 @@ func (c *context) beginStencilWithEvenOddRule() {
 
 func (c *context) endStencilWithEvenOddRule() {
 	c.ctx.StencilFunc(gles.NOTEQUAL, 0x00, 0xff)
-	c.ctx.StencilOp(gles.ZERO, gles.ZERO, gles.ZERO)
+	c.ctx.StencilOp(gles.KEEP, gles.KEEP, gles.KEEP)
 	c.ctx.ColorMask(true, true, true, true)
 }