Add AttributeOnly fields to generate SA (Set Attribute) orders

example1/example1.go

@@ -40,9 +40,19 @@ var screen1 = go3270.Screen{
 	{Row: 8, Col: 6, Intense: true, Content: "enter"},
 	{Row: 8, Col: 12, Content: "to submit your name."},
 	{Row: 10, Col: 0, Intense: true, Color: go3270.Red, Name: "errormsg"}, // a blank field for error messages
-	{Row: 14, Col: 0, Content: "Detected code page:"},
-	{Row: 14, Col: 20, Name: "codepage"},
-	{Row: 15, Col: 0, Content: "The following should be left and right square brackets: [ ]"},
+
+	// Demonstrate the AttributeOnly property:
+	{Row: 12, Col: 0, Content: "Demonstration of AttributeOnly to change format without a new field:"},
+	{Row: 13, Col: 1, AttributeOnly: true, Color: go3270.Green, Content: "████"},
+	{Row: 13, Col: 5, AttributeOnly: true, Color: go3270.Yellow, Content: "████"},
+	{Row: 13, Col: 9, AttributeOnly: true, Color: go3270.Red, Content: "████"},
+	{Row: 13, Col: 13, AttributeOnly: true, Color: go3270.Red, Highlighting: go3270.Blink, Content: "████"},
+	// When using extended attributes, need to explicitly reset to defaults, the next field won't necessarily clear the attributes out.
+	{Row: 13, Col: 17, AttributeOnly: true, Color: go3270.DefaultColor, Highlighting: go3270.DefaultHighlight},
+
+	{Row: 15, Col: 0, Content: "Detected code page:"},
+	{Row: 15, Col: 20, Name: "codepage"},
+	{Row: 16, Col: 0, Content: "The following should be left and right square brackets: [ ]"},
 	{Row: 22, Col: 0, Content: "PF3 Exit"},
 }
 

screen.go

@@ -54,6 +54,24 @@ type Field struct {
 	// is the default (i.e. no) highlighting.
 	Highlighting Highlight
 
+	// AttributeOnly will cause this "field" (which won't really be a new
+	// field) to use the SA (Set Attribute) 3270 command to change the color
+	// and highlighting of the text WITHOUT starting a new field. You can
+	// create a field at Row 5, Column 10, with AttributeOnly true, and the
+	// text will start in Roe 5, Column 10 and not skip a space to column 11
+	// like a new field would when AttributeOnly is false.
+	//
+	// If AttributeOnly is true, the Write, Autoskip, Intense, Hidden, and
+	// NumericOnly properties will have no effect. Only Highlighting and Color
+	// will affect the output, and will both default to Default (e.g. default
+	// highlighting and default color) if not specificed in this field.
+	//
+	// After using AttributeOnly to change color and highlighting, you may
+	// need to explicitly use another AttributeOnly "field" to reset to
+	// defaults, a regular (AttributeOnly = false) field may not end the
+	// attributes. (See example1.)
+	AttributeOnly bool
+
 	// Name is the name of this field, which is used to get the user-entered
 	// data. All writeable fields on a screen must have a unique name.
 	// Protected fields may also have a name to populate them dynamically when
@@ -355,9 +373,21 @@ func sba(row, col, cols int) []byte {
 }
 
 // buildField will return either an sf or sfe command depending for the
-// field.
+// field, or an sa if only setting attributes.
 func buildField(f Field) []byte {
 	var buf bytes.Buffer
+
+	if f.AttributeOnly {
+		buf.WriteByte(0x28) // sa - "set attribute"
+		// We will always set both highlighting and color bytes
+		buf.WriteByte(0x41)
+		buf.WriteByte(byte(f.Highlighting))
+		buf.WriteByte(0x28) // sa - "set attribute"
+		buf.WriteByte(0x42)
+		buf.WriteByte(byte(f.Color))
+		return buf.Bytes()
+	}
+
 	if f.Color == DefaultColor && f.Highlighting == DefaultHighlight {
 		// this is a traditional field, issue a normal sf command
 		buf.WriteByte(0x1d) // sf - "start field"