gg: keep/update commonly used event state inside the gg.Context

vlib/gg/enums.v

@@ -2,6 +2,38 @@
 // Use of this source code is governed by an MIT license that can be found in the LICENSE file.
 module gg
 
+pub enum MouseButton {
+	left = 0
+	right = 1
+	middle = 2
+	invalid = 256
+}
+
+// NB: unlike the MouseButton enum from above,
+// the [flag]-ed enum here can have combined states,
+// representing several pressed buttons at once.
+
+[flag]
+pub enum MouseButtons {
+	left
+	right
+	middle
+}
+
+[flag]
+pub enum Modifier {
+	shift // (1<<0)
+	ctrl // (1<<1)
+	alt // (1<<2)
+	super // (1<<3)
+}
+
+pub enum PenLineType {
+	solid
+	dashed
+	dotted
+}
+
 pub enum KeyCode {
 	invalid = 0
 	space = 32
@@ -126,9 +158,4 @@ pub enum KeyCode {
 	menu = 348
 }
 
-pub enum MouseButton {
-	left = 0
-	right = 1
-	middle = 2
-	invalid = 256
-}
+const key_code_max = 512