Fix bug with rendering axes

examples/dune

@@ -53,6 +53,11 @@
  (modules line)
  (libraries joy))
 
+(executable
+ (name parallel_lines)
+ (modules parallel_lines)
+ (libraries joy))
+
 (executable
  (name higher_transforms)
  (modules higher_transforms)

examples/line.ml

@@ -1,22 +1,10 @@
 open Joy
 
-let size = 800
-let interval = 16
-let line_interval = 800 / interval
-let rec range a b = if a > b then [] else a :: range (a + 1) b
-let inc x = x + 1
-
 let _ =
-  init ~size:(size, size) ();
-  let half_size = size / 2 in
-  let lines =
-    List.map
-      (fun i ->
-        let newx = i |> inc |> ( * ) line_interval in
-        line
-          ~a:(point (newx - half_size) (-half_size))
-          (point (newx - half_size) half_size))
-      (range 0 interval)
-  in
-  show lines;
+  init ();
+  let l1 = line (point 50 50) in
+  let l2 = line (point (-50) 50) in
+  let l3 = line ~a:(point (-50) 50) (point 50 50) in
+  show [l1; l2; l3];
   write ~filename:"line.png" ()
+

examples/parallel_lines.ml

@@ -0,0 +1,22 @@
+open Joy
+
+let size = 800
+let interval = 16
+let line_interval = 800 / interval
+let rec range a b = if a > b then [] else a :: range (a + 1) b
+let inc x = x + 1
+
+let _ =
+  init ~size:(size, size) ();
+  let half_size = size / 2 in
+  let lines =
+    List.map
+      (fun i ->
+        let newx = i |> inc |> ( * ) line_interval in
+        line
+          ~a:(point (newx - half_size) (-half_size))
+          (point (newx - half_size) half_size))
+      (range 0 interval)
+  in
+  show lines;
+  write ~filename:"parallel_lines.png" ()

lib/color.ml

@@ -7,6 +7,8 @@ let transparent = (0, 0, 0, 0.0)
     For use w/ `Context.background` *)
 let rgb r g b = (r, g, b, 1.0)
 
+let color ?(a = 1.0) r g b = (r, g, b, a)
+
 (** RGB code for black *)
 let black = rgb 0 0 0
 

lib/color.mli

@@ -1,6 +1,7 @@
 type color = int * int * int * float
 
 val rgb : int -> int -> int -> color
+val color : ?a:float -> int -> int -> int -> color
 
 val black : color
 val white : color

lib/joy.ml

@@ -11,19 +11,15 @@ type context = Context.context
 let show = Context.show
 let set_line_width = Context.set_line_width
 
-(* let init ?(background = Color.white) ?(line_width = 2) ?(size = (500, 500))
-    ?(axes = false) () =
-  Context.init_context (Color.opaque background) (float_of_int line_width) size
-    axes *)
-
 let init ?(size = (500, 500)) ?(line_width = 2) ?(axes = false) _ =
   let ctx = Backend_cairo.create ~background_color:Color.white ~size ~line_width ~axes in
   let ctx_container = Context.CairoContext ctx in
   Context.set_default ctx_container;
   if axes then
-    let half_w, half_h = ctx.size |> Util.tmap float_of_int |> Util.tmap ((/.) 2.) in
-    let x_axis = line ~a:{x = -.half_w; y = 0.} {x = half_w; y = 0.} in
-    let y_axis = line ~a:{x = 0.; y = -.half_h} {x = 0.; y = half_h} in
+    let half_w, half_h = ctx.size |> Util.tmap float_of_int |> Util.tmap (fun x -> x /. 2.0) in
+    let gray = Color.color 128 128 128 ~a:0.5 in
+    let x_axis = line ~a:{x = -.half_w; y = 0.} {x = half_w; y = 0.} |> with_stroke gray in
+    let y_axis = line ~a:{x = 0.; y = -.half_h} {x = 0.; y = half_h} |> with_stroke gray in
     show ~ctx:ctx_container [x_axis; y_axis]
 
 let write ?(filename = "joy.png") () =