[doc] Document the visualization protobuf file

proto/visualization/ssl_visualization.proto

@@ -1,37 +1,71 @@
 syntax = "proto3";
 
+// Color encoded in RGB
 message RgbColor {
+    // red (0-255)
     uint32 r = 1;
+    // green (0-255)
     uint32 g = 2;
+    // blue (0-255)
     uint32 b = 3;
+    // alpha (0.0-1.0)
     float a = 4;
 }
 
+// Metadata for each shape
 message Metadata {
+    // layer name, optionally with a hierarchy
     repeated string layer = 1;
+    // Should a client show this by default?
     bool visibleByDefault = 2;
+    // An order number:
+    // <0: Below field lines
+    // 0: default
+    // 1: robots
+    // 2: robot ids
+    // 3: ball
+    // >3: above vision objects
     int32 order = 3;
+    // Color to fill the shape
     RgbColor color_fill = 4;
+    // Color for the shape stroke
     RgbColor color_stroke = 5;
 }
 
+// A line segment
 message LineSegment {
+    // The metadata
     Metadata metadata = 1;
+    // Start point, x value [m]
     float start_x = 2;
+    // Start point, y value [m]
     float start_y = 3;
+    // End point, x value [m]
     float end_x = 4;
+    // End point, y value [m]
     float end_y = 5;
 }
 
+// A full circle
 message Circle {
+    // The metadata
     Metadata metadata = 1;
+    // Center point, x value [m]
     float center_x = 2;
+    // Center point, y value [m]
     float center_y = 3;
+    // Radius [m]
     float radius = 4;
 }
 
+// Wrapper frame containing all shapes
 message VisualizationFrame {
+    // An identifier for the sender
+    // Used to identify the source of shapes in a client
+    // Also used to keep track of the latest frame of each sender in clients, if there a multiple ones senders
     string sender_id = 1;
+    // all lines
     repeated LineSegment lines = 2;
+    // all circles
     repeated Circle circles = 3;
 }