keep triangle stages (clicked positions) drawn on screen, until triangle stages resets to NO_TRIANGLE

functional-core/app-type.sml

@@ -18,6 +18,8 @@ sig
   type app_type = {triangleStage: triangle_stage, triangles: triangle list}
 
   val initial: app_type
+
+  val withTriangleStage: app_type * triangle_stage -> app_type
 end
 
 structure AppType :> APP_TYPE =
@@ -48,4 +50,10 @@ struct
   type app_type = {triangles: triangle list, triangleStage: triangle_stage}
 
   val initial = {triangles = [], triangleStage = NO_TRIANGLE}
+
+  fun withTriangleStage (app: app_type, newTriangleStage: triangle_stage) :
+    app_type =
+    let val {triangles, triangleStage = _} = app
+    in {triangles = triangles, triangleStage = newTriangleStage}
+    end
 end

functional-core/app-update.sml

@@ -150,6 +150,7 @@ struct
         MOUSE_MOVE {x = mouseX, y = mouseY} =>
           let
             val (drawVec, _, _) = getClickPos (mouseX, mouseY, 1.0, 0.0, 0.0)
+            val drawVec = getTriangleStageVector (model, drawVec)
             val drawMsg = DRAW_BUTTON drawVec
           in
             (model, drawMsg, mouseX, mouseY)
@@ -157,21 +158,52 @@ struct
       | MOUSE_LEFT_RELEASE =>
           let
             val (drawVec, _, _) = getClickPos (mouseX, mouseY, 1.0, 0.0, 0.0)
+            val drawVec = getTriangleStageVector (model, drawVec)
             val drawMsg = DRAW_BUTTON drawVec
           in
             (model, drawMsg, mouseX, mouseY)
           end
       | MUSE_LEFT_CLICK =>
           let
-            val (buttonVec, hpos, vpos) = 
+            val (buttonVec, hpos, vpos) = getClickPos
-              getClickPos (mouseX, mouseY, 0.0, 0.0, 1.0)
+              (mouseX, mouseY, 0.0, 0.0, 1.0)
           in
             if Vector.length buttonVec > 0 then
-              let
+              (case #triangleStage model of
-                val drawMsg = DRAW_BUTTON buttonVec
+                 NO_TRIANGLE =>
-              in
+                   let
-                (model, drawMsg, mouseX, mouseY)
+                     val drawVec = getTriangleStageVector (model, buttonVec)
-              end
+                     val drawMsg = DRAW_BUTTON drawVec
+
+                     val newTriangleStage = FIRST {x1 = hpos, y1 = vpos}
+                     val model =
+                       AppType.withTriangleStage (model, newTriangleStage)
+                   in
+                     (model, drawMsg, mouseX, mouseY)
+                   end
+               | FIRST {x1, y1} =>
+                   let
+                     val drawVec = getTriangleStageVector (model, buttonVec)
+                     val drawMsg = DRAW_BUTTON drawVec
+
+                     val newTriangleStage = SECOND
+                       {x1 = x1, y1 = y1, x2 = hpos, y2 = vpos}
+                     val model =
+                       AppType.withTriangleStage (model, newTriangleStage)
+                   in
+                     (model, drawMsg, mouseX, mouseY)
+                   end
+               | SECOND {x1, y1, x2, y2} =>
+                   let
+                     val drawVec = getTriangleStageVector (model, buttonVec)
+                     val drawMsg = DRAW_BUTTON drawVec
+
+                     val newTriangleStage = NO_TRIANGLE
+                     val model =
+                       AppType.withTriangleStage (model, newTriangleStage)
+                   in
+                     (model, drawMsg, mouseX, mouseY)
+                   end)
             else
               (model, NO_DRAW, mouseX, mouseY)
           end