shader: Reland: Add a predefined uniform variable: __viewportSize

examples/shader/main.go

@@ -29,17 +29,20 @@ const (
 
 const shaderSrc = `package main
 
+// __viewportSize is a predefined uniform variable.
+// TODO: Hide this by a function.
+
 func Vertex(position vec2, texCoord vec2, color vec4) vec4 {
 	return mat4(
-		2.0/640, 0, 0, 0,
-		0, 2.0/480, 0, 0,
+		2.0/__viewportSize.x, 0, 0, 0,
+		0, 2.0/__viewportSize.y, 0, 0,
 		0, 0, 1, 0,
 		-1, -1, 0, 1,
 	) * vec4(position, 0, 1)
 }
 
 func Fragment(position vec4) vec4 {
-	return vec4(position.x/640, position.y/480, 0, 1)
+	return vec4(position.x/__viewportSize.x, position.y/__viewportSize.y, 0, 1)
 }`
 
 type Game struct {

image.go

@@ -384,6 +384,10 @@ func (i *Image) DrawTrianglesWithShader(vertices []Vertex, indices []uint16, sha
 		}
 	}
 
+	// The first uniform variable is Internal_ViewportSize.
+	// The actual value is set at graphicscommand package.
+	us = append([]interface{}{[]float32{0, 0}}, us...)
+
 	var bx0, by0, bx1, by1 float32
 	if firstImage != nil {
 		b := firstImage.Bounds()

internal/graphicscommand/command.go

@@ -453,6 +453,13 @@ func (c *drawTrianglesCommand) Exec(indexOffset int) error {
 				us[i] = v
 			}
 		}
+
+		// The last uniform variables are added at /shader.go and represents a viewport size.
+		w, h := c.dst.InternalSize()
+		viewport := us[0].([]float32)
+		viewport[0] = float32(w)
+		viewport[1] = float32(h)
+
 		return theGraphicsDriver.DrawShader(c.dst.image.ID(), c.shader.shader.ID(), c.nindices, indexOffset, c.mode, us)
 	}
 	return theGraphicsDriver.Draw(c.dst.image.ID(), c.src.image.ID(), c.nindices, indexOffset, c.mode, c.color, c.filter, c.address)

internal/graphicscommand/image_test.go

@@ -94,7 +94,7 @@ func TestShader(t *testing.T) {
 	ir := etesting.ShaderProgramFill(0xff, 0, 0, 0xff)
 	s := NewShader(&ir)
 	us := []interface{}{
-		[]float32{w, h},
+		[]float32{0, 0},
 	}
 	dst.DrawTriangles(nil, vs, is, nil, driver.CompositeModeSourceOver, 0, 0, s, us)
 

internal/restorable/shader_test.go

@@ -36,7 +36,7 @@ func TestShader(t *testing.T) {
 	ir := etesting.ShaderProgramFill(0xff, 0, 0, 0xff)
 	s := NewShader(&ir)
 	us := []interface{}{
-		0: []float32{1, 1},
+		[]float32{0, 0},
 	}
 	img.DrawTriangles(nil, quadVertices(1, 1, 0, 0), graphics.QuadIndices(), nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressClampToZero, s, us)
 
@@ -73,7 +73,7 @@ func TestShaderChain(t *testing.T) {
 	s := NewShader(&ir)
 	for i := 0; i < num-1; i++ {
 		us := []interface{}{
-			[]float32{1, 1},
+			[]float32{0, 0},
 			imgs[i],
 		}
 		imgs[i+1].DrawTriangles(nil, quadVertices(1, 1, 0, 0), graphics.QuadIndices(), nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressClampToZero, s, us)
@@ -113,7 +113,7 @@ func TestShaderMultipleSources(t *testing.T) {
 	ir := etesting.ShaderProgramImages(3)
 	s := NewShader(&ir)
 	us := []interface{}{
-		[]float32{1, 1},
+		[]float32{0, 0},
 		srcs[0],
 		srcs[1],
 		[]float32{0, 0, 1, 1},
@@ -150,7 +150,7 @@ func TestShaderDispose(t *testing.T) {
 	ir := etesting.ShaderProgramFill(0xff, 0, 0, 0xff)
 	s := NewShader(&ir)
 	us := []interface{}{
-		[]float32{1, 1},
+		[]float32{0, 0},
 	}
 	img.DrawTriangles(nil, quadVertices(1, 1, 0, 0), graphics.QuadIndices(), nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressClampToZero, s, us)
 

internal/shader/shader.go

@@ -136,6 +136,26 @@ func (cs *compileState) parse(f *ast.File) {
 			cs.parseDecl(&cs.global, d)
 		}
 	}
+
+	// Sort the uniform variable so that special variable starting with __ should come first.
+	var unames []string
+	var utypes []shaderir.Type
+	for i, u := range cs.uniforms {
+		if strings.HasPrefix(u, "__") {
+			unames = append(unames, u)
+			utypes = append(utypes, cs.ir.Uniforms[i])
+		}
+	}
+	for i, u := range cs.uniforms {
+		if !strings.HasPrefix(u, "__") {
+			unames = append(unames, u)
+			utypes = append(utypes, cs.ir.Uniforms[i])
+		}
+	}
+	cs.uniforms = unames
+	cs.ir.Uniforms = utypes
+
+	// Parse functions.
 	for _, d := range f.Decls {
 		if _, ok := d.(*ast.FuncDecl); ok {
 			cs.parseDecl(&cs.global, d)
@@ -175,10 +195,12 @@ func (cs *compileState) parseDecl(b *block, d ast.Decl) {
 				vs := cs.parseVariable(b, s)
 				if b == &cs.global {
 					for i, v := range vs {
-						if v.name[0] < 'A' || 'Z' < v.name[0] {
-							cs.addError(s.Names[i].Pos(), fmt.Sprintf("global variables must be exposed: %s", v.name))
+						if !strings.HasPrefix(v.name, "__") {
+							if v.name[0] < 'A' || 'Z' < v.name[0] {
+								cs.addError(s.Names[i].Pos(), fmt.Sprintf("global variables must be exposed: %s", v.name))
+							}
 						}
-						// TODO: Check init
+						// TODO: Check rhs
 						cs.uniforms = append(cs.uniforms, v.name)
 						cs.ir.Uniforms = append(cs.ir.Uniforms, v.typ.ir)
 					}

internal/testing/shader.go

@@ -192,7 +192,7 @@ var (
 func defaultProgram() shaderir.Program {
 	return shaderir.Program{
 		Uniforms: []shaderir.Type{
-			{Main: shaderir.Vec2},
+			{Main: shaderir.Vec2}, // Viewport size. This must be the first uniform variable, and the values are set at graphicscommand driver.
 		},
 		Attributes: []shaderir.Type{
 			{Main: shaderir.Vec2}, // Local var (0) in the vertex shader

shader.go

@@ -15,6 +15,7 @@
 package ebiten
 
 import (
+	"bytes"
 	"go/parser"
 	"go/token"
 
@@ -22,13 +23,20 @@ import (
 	"github.com/hajimehoshi/ebiten/internal/shader"
 )
 
+const shaderSuffix = `
+var __viewportSize vec2`
+
 type Shader struct {
 	shader *buffered.Shader
 }
 
 func NewShader(src []byte) (*Shader, error) {
+	var buf bytes.Buffer
+	buf.Write(src)
+	buf.WriteString(shaderSuffix)
+
 	fs := token.NewFileSet()
-	f, err := parser.ParseFile(fs, "", src, parser.AllErrors)
+	f, err := parser.ParseFile(fs, "", buf.Bytes(), parser.AllErrors)
 	if err != nil {
 		return nil, err
 	}