add background for F3 text, fix single-channel texture display

internal/igwrap/wrap.go

@@ -21,6 +21,20 @@ func Text(format string, a ...interface{}) {
 	imgui.Text(fmt.Sprintf(format, a...))
 }
 
+// TextBackground wraps imgui.Text to create a
+// shortcut for fmt.Sprintf.
+//
+// It also fills the background of the text with the given color.
+func TextBackground(color itype.Vec4f, padding itype.Vec2f, format string, a ...interface{}) {
+	text := fmt.Sprintf(format, a...)
+	orig := imgui.CursorScreenPos()
+	size := imgui.CalcTextSize(text, false, 0)
+	halfpad := padding.Multiply(0.5)
+	imgui.BackgroundDrawList().AddRectFilledV(orig.Minus(Vec2(halfpad)), orig.Plus(size).Plus(Vec2(halfpad)), PackedColor(color), 0, 0)
+
+	imgui.Text(text)
+}
+
 // Begin wraps imgui.BeginV to create a
 // easy-to-use and intuitive interface.
 //