shader: Implement 'for' statement

Fixes #1230

internal/shader/shader.go

@@ -24,8 +24,9 @@ import (
 )
 
 type variable struct {
-	name string
-	typ  shaderir.Type
+	name           string
+	typ            shaderir.Type
+	forLoopCounter bool
 }
 
 type constant struct {
@@ -645,6 +646,10 @@ func (cs *compileState) parseBlock(outer *block, stmts []ast.Stmt, inParams, out
 			offset = len(inParams) + len(outParams)
 		}
 		for _, v := range block.vars[offset:] {
+			if v.forLoopCounter {
+				block.ir.LocalVars = append(block.ir.LocalVars, shaderir.Type{})
+				continue
+			}
 			block.ir.LocalVars = append(block.ir.LocalVars, v.typ)
 		}
 	}()

internal/shader/stmt.go

@@ -113,6 +113,163 @@ func (cs *compileState) parseStmt(block *block, stmt ast.Stmt, inParams []variab
 			return nil, false
 		}
 		stmts = append(stmts, ss...)
+
+	case *ast.ForStmt:
+		msg := "for-statement must follow this format: for (varname) := (constant); (varname) (op) (constant); (varname) (op) (constant) { ..."
+		if stmt.Init == nil {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		if stmt.Cond == nil {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		if stmt.Post == nil {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+
+		// Create a new pseudo block for the initial statement, so that the counter variable belongs to the
+		// new pseudo block for each for-loop. Without this, the samely named counter variables in different
+		// for-loops confuses the parser.
+		pseudoBlock, ok := cs.parseBlock(block, []ast.Stmt{stmt.Init}, inParams, nil)
+		if !ok {
+			return nil, false
+		}
+		ss := pseudoBlock.ir.Stmts
+
+		if len(ss) != 1 {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		if ss[0].Type != shaderir.Assign {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		if ss[0].Exprs[0].Type != shaderir.LocalVariable {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		varidx := ss[0].Exprs[0].Index
+		if ss[0].Exprs[1].Type != shaderir.NumberExpr {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+
+		vartype := pseudoBlock.vars[0].typ
+		init := ss[0].Exprs[1].Const
+
+		exprs, ts, ss, ok := cs.parseExpr(pseudoBlock, stmt.Cond)
+		if !ok {
+			return nil, false
+		}
+		if len(exprs) != 1 {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		if len(ts) != 1 || ts[0].Main != shaderir.Bool {
+			cs.addError(stmt.Pos(), "for-statement's condition must be bool")
+			return nil, false
+		}
+		if len(ss) != 0 {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		if exprs[0].Type != shaderir.Binary {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		op := exprs[0].Op
+		if op != shaderir.LessThanOp && op != shaderir.LessThanEqualOp && op != shaderir.GreaterThanOp && op != shaderir.GreaterThanEqualOp && op != shaderir.EqualOp && op != shaderir.NotEqualOp {
+			cs.addError(stmt.Pos(), "for-statement's condition must have one of these operators: <, <=, >, >=, ==, !=")
+			return nil, false
+		}
+		if exprs[0].Exprs[0].Type != shaderir.LocalVariable {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		if exprs[0].Exprs[0].Index != varidx {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		if exprs[0].Exprs[1].Type != shaderir.NumberExpr {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		end := exprs[0].Exprs[1].Const
+
+		postSs, ok := cs.parseStmt(pseudoBlock, stmt.Post, inParams)
+		if !ok {
+			return nil, false
+		}
+		if len(postSs) != 1 {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		if postSs[0].Type != shaderir.Assign {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		if postSs[0].Exprs[0].Type != shaderir.LocalVariable {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		if postSs[0].Exprs[0].Index != varidx {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		if postSs[0].Exprs[1].Type != shaderir.Binary {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		if postSs[0].Exprs[1].Exprs[0].Type != shaderir.LocalVariable {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		if postSs[0].Exprs[1].Exprs[0].Index != varidx {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		if postSs[0].Exprs[1].Exprs[1].Type != shaderir.NumberExpr {
+			cs.addError(stmt.Pos(), msg)
+			return nil, false
+		}
+		delta := postSs[0].Exprs[1].Exprs[1].Const
+		switch postSs[0].Exprs[1].Op {
+		case shaderir.Add:
+		case shaderir.Sub:
+			delta = gconstant.UnaryOp(token.SUB, delta, 0)
+		default:
+			cs.addError(stmt.Pos(), "for-statement's post statement must have one of these operators: +=, -=, ++, --")
+			return nil, false
+		}
+
+		b, ok := cs.parseBlock(pseudoBlock, []ast.Stmt{stmt.Body}, inParams, nil)
+		if !ok {
+			return nil, false
+		}
+		bodyir := b.ir
+		for len(bodyir.Stmts) == 1 && bodyir.Stmts[0].Type == shaderir.BlockStmt {
+			bodyir = bodyir.Stmts[0].Blocks[0]
+		}
+
+		// As the pseudo block is not actually used, copy the variable part to the actual block.
+		// This must be done after parsing the for-loop is done, or the duplicated variables confuses the
+		// parsing.
+		block.vars = append(block.vars, pseudoBlock.vars[0])
+		block.vars[len(block.vars)-1].forLoopCounter = true
+
+		stmts = append(stmts, shaderir.Stmt{
+			Type:        shaderir.For,
+			Blocks:      []shaderir.Block{bodyir},
+			ForVarType:  vartype,
+			ForVarIndex: varidx,
+			ForInit:     init,
+			ForEnd:      end,
+			ForOp:       op,
+			ForDelta:    delta,
+		})
+
 	case *ast.IfStmt:
 		if stmt.Init != nil {
 			init := stmt.Init
@@ -123,10 +280,8 @@ func (cs *compileState) parseStmt(block *block, stmt ast.Stmt, inParams []variab
 			}
 
 			stmts = append(stmts, shaderir.Stmt{
-				Type: shaderir.BlockStmt,
-				Blocks: []shaderir.Block{
-					b.ir,
-				},
+				Type:   shaderir.BlockStmt,
+				Blocks: []shaderir.Block{b.ir},
 			})
 			return stmts, true
 		}
@@ -174,6 +329,7 @@ func (cs *compileState) parseStmt(block *block, stmt ast.Stmt, inParams []variab
 			Exprs:  exprs,
 			Blocks: bs,
 		})
+
 	case *ast.IncDecStmt:
 		exprs, _, ss, ok := cs.parseExpr(block, stmt.X)
 		if !ok {
@@ -205,6 +361,7 @@ func (cs *compileState) parseStmt(block *block, stmt ast.Stmt, inParams []variab
 				},
 			},
 		})
+
 	case *ast.ReturnStmt:
 		for i, r := range stmt.Results {
 			exprs, _, ss, ok := cs.parseExpr(block, r)
@@ -233,6 +390,7 @@ func (cs *compileState) parseStmt(block *block, stmt ast.Stmt, inParams []variab
 		stmts = append(stmts, shaderir.Stmt{
 			Type: shaderir.Return,
 		})
+
 	case *ast.ExprStmt:
 		exprs, _, ss, ok := cs.parseExpr(block, stmt.X)
 		if !ok {
@@ -249,6 +407,7 @@ func (cs *compileState) parseStmt(block *block, stmt ast.Stmt, inParams []variab
 				Exprs: []shaderir.Expr{expr},
 			})
 		}
+
 	default:
 		cs.addError(stmt.Pos(), fmt.Sprintf("unexpected statement: %#v", stmt))
 		return nil, false

internal/shader/testdata/for.expected.vs

@@ -0,0 +1,14 @@
+void F0(out vec2 l0) {
+	vec2 l1 = vec2(0);
+	vec2 l3 = vec2(0);
+	l1 = vec2(0.0);
+	for (int l2 = 0; l2 < 100; l2++) {
+		(l1).x = ((l1).x) + (1);
+	}
+	l3 = vec2(0.0);
+	for (float l4 = 10.0; l4 >= 0.0; l4 -= 2.0) {
+		(l3).x = ((l3).x) - (1);
+	}
+	l0 = l1;
+	return;
+}

internal/shader/testdata/for.go

@@ -0,0 +1,13 @@
+package main
+
+func Foo() vec2 {
+	v := vec2(0)
+	for i := 0; i < 100; i++ {
+		v.x++
+	}
+	v2 := vec2(0)
+	for i := 10.0; i >= 0; i -= 2 {
+		v2.x--
+	}
+	return v
+}

internal/shaderir/glsl.go

@@ -265,7 +265,10 @@ func (p *Program) glslBlock(topBlock, block *Block, level int, localVarIndex int
 
 	var lines []string
 	for _, t := range block.LocalVars {
-		lines = append(lines, fmt.Sprintf("%s%s = %s;", idt, p.glslVarDecl(&t, fmt.Sprintf("l%d", localVarIndex)), p.glslVarInit(&t)))
+		// The type is None e.g., when the variable is a for-loop counter.
+		if t.Main != None {
+			lines = append(lines, fmt.Sprintf("%s%s = %s;", idt, p.glslVarDecl(&t, fmt.Sprintf("l%d", localVarIndex)), p.glslVarInit(&t)))
+		}
 		localVarIndex++
 	}