Added bounds checking to NewArea() and Area.SetSize() such that an Area must have a valid size.

area.go

@@ -3,6 +3,7 @@
 package ui
 
 import (
+	"fmt"
 	"sync"
 	"image"
 )
@@ -10,6 +11,7 @@ import (
 // Area represents a blank canvas upon which programs may draw anything and receive arbitrary events from the user.
 // An Area has an explicit size, represented in pixels, that may be different from the size shown in its Window; Areas have horizontal and vertical scrollbars that are hidden when not needed.
 // The coordinate system of an Area always has an origin of (0,0) which maps to the top-left corner; all image.Points and image.Rectangles sent across Area's channels conform to this.
+// The size of an Area must be at least 1x1 (that is, neither its width nor its height may be zero or negative).
 // 
 // To handle events to the Area, an Area must be paired with an AreaHandler.
 // See AreaHandler for details.
@@ -260,9 +262,16 @@ const (
 	// TODO add Super
 )
 
+func checkAreaSize(width int, height int, which string) {
+	if width <= 0 || height <= 0 {
+		panic(fmt.Errorf("invalid size %dx%d in %s", width, height, which))
+	}
+}
+
 // NewArea creates a new Area with the given size and handler.
-// It panics if handler is nil.
+// It panics if handler is nil or if width or height is zero or negative.
 func NewArea(width int, height int, handler AreaHandler) *Area {
+	checkAreaSize(width, height, "NewArea()")
 	if handler == nil {
 		panic("handler passed to NewArea() must not be nil")
 	}
@@ -276,10 +285,12 @@ func NewArea(width int, height int, handler AreaHandler) *Area {
 
 // SetSize sets the Area's internal drawing size.
 // It has no effect on the actual control size.
+// It panics if width or height is zero or negative.
 func (a *Area) SetSize(width int, height int) {
 	a.lock.Lock()
 	defer a.lock.Unlock()
 
+	checkAreaSize(width, height, "Area.SetSize()")
 	if a.created {
 		a.sysData.setAreaSize(width, height)
 		return

test/main.go

@@ -78,6 +78,7 @@ func invalidTest(c *Combobox, l *Listbox, s *Stack, g *Grid) {
 	func() {
 		defer x("Listbox.Delete > len"); l.Delete(c.Len() + 5); panic(nil)
 	}()
+	// TODO get rid of arg != nil by creating dummy arg
 	if s != nil {
 		func() {
 			defer x("Stack.SetStretchy < 0"); s.SetStretchy(-5); panic(nil)
@@ -86,6 +87,7 @@ func invalidTest(c *Combobox, l *Listbox, s *Stack, g *Grid) {
 			defer x("Stack.SetStretchy > len"); s.SetStretchy(5555); panic(nil)
 		}()
 	}
+	// TODO grid creation checks
 	if g != nil {
 		func() {
 			defer x("Grid.SetFilling x < 0"); g.SetFilling(-5, 0); panic(nil)
@@ -112,6 +114,33 @@ func invalidTest(c *Combobox, l *Listbox, s *Stack, g *Grid) {
 			defer x("Grid.SetStretchy y > len"); g.SetStretchy(0, 5555); panic(nil)
 		}()
 	}
+	ah := &areaHandler{nil}
+	type at struct {
+		msg		string
+		x, y		int
+	}
+	var ats = []at{
+		at{"width < 0", -5, 5},
+		at{"width == 0", 0, 5},
+		at{"height < 0", 5, -5},
+		at{"height == 0", 5, 0},
+		at{"width/heght < 0", -5, -5},
+		at{"width < 0/height == 0", -5, 0},
+		at{"width == 0/height < 0", 0, -5},
+		at{"width/height == 0", 0, 0},
+	}
+	for _, q := range ats {
+		func() {
+			defer x("NewArea() " + q.msg); NewArea(q.x, q.y, ah); panic(nil)
+		}()
+	}
+	// no need to pass this in as an argument since it's handled by the portable code, not by sysData
+	a := NewArea(50, 50, ah)
+	for _, q := range ats {
+		func() {
+			defer x("Area.SetSize() " + q.msg); a.SetSize(q.x, q.y); panic(nil)
+		}()
+	}
 	MsgBox("test", "all working as intended")
 }
 

todo.md

@@ -1,5 +1,4 @@
 so I don't forget:
-- add bounds checking to Area's sizing methods
 - describe thread-safety of Area.SetSize()
 - should all instances of -1 as error returns from Windows functions be changed to ^0 or does the uintptr() conversion handle sign extension?