ebiten: add Vertex.Custom0 to Custom3

Closes #2640

image.go

@@ -295,6 +295,13 @@ type Vertex struct {
 	ColorG float32
 	ColorB float32
 	ColorA float32
+
+	// Custom0/Custom1/Custom2/Custom3 represents general-purpose values passed to the shader.
+	// In order to use them, Fragment must have an additional vec4 argument.
+	Custom0 float32
+	Custom1 float32
+	Custom2 float32
+	Custom3 float32
 }
 
 var _ [0]byte = [unsafe.Sizeof(Vertex{}) - unsafe.Sizeof(float32(0))*graphics.VertexFloatCount]byte{}
@@ -668,6 +675,10 @@ func (i *Image) DrawTrianglesShader(vertices []Vertex, indices []uint16, shader
 		vs[i*graphics.VertexFloatCount+5] = v.ColorG
 		vs[i*graphics.VertexFloatCount+6] = v.ColorB
 		vs[i*graphics.VertexFloatCount+7] = v.ColorA
+		vs[i*graphics.VertexFloatCount+8] = v.Custom0
+		vs[i*graphics.VertexFloatCount+9] = v.Custom1
+		vs[i*graphics.VertexFloatCount+10] = v.Custom2
+		vs[i*graphics.VertexFloatCount+11] = v.Custom3
 	}
 
 	is := i.ensureTmpIndices(len(indices))

internal/graphics/shader.go

@@ -154,8 +154,8 @@ func imageSrc%[1]dAt(pos vec2) vec4 {
 	shaderSuffix += `
 var __projectionMatrix mat4
 
-func __vertex(dstPos vec2, srcPos vec2, color vec4) (vec4, vec2, vec4) {
-	return __projectionMatrix * vec4(dstPos, 0, 1), srcPos, color
+func __vertex(dstPos vec2, srcPos vec2, color vec4, custom vec4) (vec4, vec2, vec4, vec4) {
+	return __projectionMatrix * vec4(dstPos, 0, 1), srcPos, color, custom
 }
 `
 	return shaderSuffix, nil

internal/graphics/vertex.go

@@ -39,7 +39,7 @@ const (
 )
 
 const (
-	VertexFloatCount = 8
+	VertexFloatCount = 12
 )
 
 var (

internal/shader/shader.go

@@ -345,10 +345,10 @@ func (cs *compileState) parse(f *ast.File) {
 	// Check varying variables.
 	// In testings, there might not be vertex and fragment entry points.
 	if len(vertexOutParams) > 0 && len(fragmentInParams) > 0 {
-		if len(vertexOutParams) != len(fragmentInParams) {
-			cs.addError(0, "the number of vertex entry point's returning values and the number of fragment entry point's params must be the same")
-		}
 		for i, t := range vertexOutParams {
+			if len(fragmentInParams) <= i {
+				break
+			}
 			if !t.Equal(&fragmentInParams[i]) {
 				cs.addError(0, "vertex entry point's returning value types and fragment entry point's param types must match")
 			}
@@ -373,7 +373,7 @@ func (cs *compileState) parse(f *ast.File) {
 		return
 	}
 
-	// Set attribute varying veraibles.
+	// Set attribute and varying veraibles.
 	cs.ir.Attributes = append(cs.ir.Attributes, vertexInParams...)
 	if len(vertexOutParams) > 0 {
 		// TODO: Check that these params are not arrays or structs
@@ -820,6 +820,18 @@ func (cs *compileState) parseFunc(block *block, d *ast.FuncDecl) (function, bool
 	}
 
 	inParams, outParams, returnType := cs.parseFuncParams(block, d.Name.Name, d)
+	if d.Name.Name == cs.fragmentEntry {
+		// The 0th inParams is a special variable for position and is not included in varying variables.
+		if diff := len(cs.ir.Varyings) - (len(inParams) - 1); diff > 0 {
+			// inParams is not enough when the vertex shader has more returning values than the fragment shader's arguments.
+			for i := 0; i < diff; i++ {
+				inParams = append(inParams, variable{
+					name: "_",
+					typ:  cs.ir.Varyings[len(inParams)-1+i],
+				})
+			}
+		}
+	}
 	b, ok := cs.parseBlock(block, d.Name.Name, d.Body.List, inParams, outParams, returnType, true)
 	if !ok {
 		return function{}, false

shader_test.go

@@ -2595,3 +2595,90 @@ func Fragment(dstPos vec4, srcPos vec2, color vec4) vec4 {
 		}
 	}
 }
+
+func TestShaderCustomValues(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, custom vec4) vec4 {
+	return custom
+}
+`))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	clr := color.RGBA{R: 0x10, G: 0x20, B: 0x30, A: 0x40}
+	dst.DrawTrianglesShader([]ebiten.Vertex{
+		{
+			DstX:    0,
+			DstY:    0,
+			SrcX:    0,
+			SrcY:    0,
+			ColorR:  1,
+			ColorG:  1,
+			ColorB:  1,
+			ColorA:  1,
+			Custom0: float32(clr.R) / 0xff,
+			Custom1: float32(clr.G) / 0xff,
+			Custom2: float32(clr.B) / 0xff,
+			Custom3: float32(clr.A) / 0xff,
+		},
+		{
+			DstX:    w,
+			DstY:    0,
+			SrcX:    w,
+			SrcY:    0,
+			ColorR:  1,
+			ColorG:  1,
+			ColorB:  1,
+			ColorA:  1,
+			Custom0: float32(clr.R) / 0xff,
+			Custom1: float32(clr.G) / 0xff,
+			Custom2: float32(clr.B) / 0xff,
+			Custom3: float32(clr.A) / 0xff,
+		},
+		{
+			DstX:    0,
+			DstY:    h,
+			SrcX:    0,
+			SrcY:    h,
+			ColorR:  1,
+			ColorG:  1,
+			ColorB:  1,
+			ColorA:  1,
+			Custom0: float32(clr.R) / 0xff,
+			Custom1: float32(clr.G) / 0xff,
+			Custom2: float32(clr.B) / 0xff,
+			Custom3: float32(clr.A) / 0xff,
+		},
+		{
+			DstX:    w,
+			DstY:    h,
+			SrcX:    w,
+			SrcY:    h,
+			ColorR:  1,
+			ColorG:  1,
+			ColorB:  1,
+			ColorA:  1,
+			Custom0: float32(clr.R) / 0xff,
+			Custom1: float32(clr.G) / 0xff,
+			Custom2: float32(clr.B) / 0xff,
+			Custom3: float32(clr.A) / 0xff,
+		},
+	}, []uint16{0, 1, 2, 1, 2, 3}, s, nil)
+
+	for j := 0; j < h; j++ {
+		for i := 0; i < w; i++ {
+			got := dst.At(i, j).(color.RGBA)
+			want := clr
+			if !sameColors(got, want, 2) {
+				t.Errorf("dst.At(%d, %d): got: %v, want: %v", i, j, got, want)
+			}
+		}
+	}
+}