add buttonDrawObject and calls to successfully draw button

imperative-shell/app-draw.sml

@@ -46,7 +46,7 @@ struct
           , Vector.length Constants.graphLines
           , Gles3.STATIC_DRAW ()
           )
-      val _ = Gles3.vertexAttribPointer (0, 2)
+      val _ = Gles3.vertexAttribPointer (0, 2, 2, 0)
       val _ = Gles3.enableVertexAttribArray 0
     in
       graphDrawObject
@@ -54,11 +54,70 @@ struct
 
   fun drawGraphLines (graphDrawObject: draw_object) =
     let
-      val {program, ...} = graphDrawObject
-      val _ = Gles3.useProgram (program)
+      val {vertexBuffer, program, ...} = graphDrawObject
+      val _ = Gles3.bindBuffer vertexBuffer
+      val _ = Gles3.vertexAttribPointer (0, 2, 2, 0)
+      val _ = Gles3.enableVertexAttribArray 0
+      val _ = Gles3.useProgram program
       val _ = Gles3.drawArrays
         (Gles3.TRIANGLES (), 0, Vector.length Constants.graphLines div 2)
     in
       ()
     end
+
+  val buttonVec =
+   #[ 0.5, 0.5, 1.0, 0.0, 0.0
+    , 0.5, ~0.5, 1.0, 0.0, 0.0
+    , ~0.5, 0.5, 1.0, 0.0, 0.0
+
+    , 0.5, ~0.5, 0.0, 0.0, 1.0
+    , ~0.5, ~0.5, 0.0, 0.0, 1.0
+    , ~0.5, 0.5, 0.0, 0.0, 1.0
+    ]
+
+  fun initButton () =
+    let
+      val buttonDrawObject = initDrawObject
+        ( Constants.colouredVertexShaderString
+        , Constants.colouredFragmentShaderString
+        )
+      val {vertexBuffer, program, ...} = buttonDrawObject
+
+      val _ = Gles3.bindBuffer vertexBuffer
+      val _ =
+        Gles3.bufferData
+          (buttonVec, Vector.length buttonVec, Gles3.STATIC_DRAW ())
+      val _ = Gles3.vertexAttribPointer (0, 2, 5, 0)
+      val _ = Gles3.enableVertexAttribArray 0
+
+      val _ = Gles3.vertexAttribPointer (1, 3, 5, 8)
+      val _ = Gles3.enableVertexAttribArray 1
+    in
+      buttonDrawObject
+    end
+
+  fun uploadButtonVector (buttonDrawObject: draw_object, vec) =
+    let
+      val {vertexBuffer, ...} = buttonDrawObject
+      val _ = Gles3.bindBuffer vertexBuffer
+      val _ = Gles3.bufferData (vec, Vector.length vec, Gles3.STATIC_DRAW ())
+    in
+      ()
+    end
+
+  fun drawButton (buttonDrawObject: draw_object, vec) =
+    let
+      val {vertexBuffer, program, ...} = buttonDrawObject
+      val _ = Gles3.bindBuffer vertexBuffer
+      val _ = Gles3.vertexAttribPointer (0, 2, 5, 0)
+      val _ = Gles3.enableVertexAttribArray 0
+      val _ = Gles3.vertexAttribPointer (1, 3, 5, 8)
+      val _ = Gles3.enableVertexAttribArray 1
+      val _ = Gles3.useProgram program
+      val _ = Gles3.drawArrays
+        (Gles3.TRIANGLES (), 0, Vector.length buttonVec div 5)
+    in
+      ()
+    end
+
 end

imperative-shell/constants.sml

@@ -17,6 +17,27 @@ struct
     \   FragColor = vec4(0.0f, 0.0f, 0.0f, 1.0f);\n\
     \}"
 
+  val colouredVertexShaderString =
+    "#version 300 es\n\
+    \layout (location = 0) in vec2 apos;\n\
+    \layout (location = 1) in vec3 col;\n\
+    \out vec3 frag_col;\n\
+    \void main()\n\
+    \{\n\
+    \   frag_col = col;\n\
+    \   gl_Position = vec4(apos.x, apos.y, 0.0f, 1.0f);\n\
+    \}"
+
+  val colouredFragmentShaderString =
+    "#version 300 es\n\
+    \precision mediump float;\n\
+    \in vec3 frag_col;\n\
+    \out vec4 FragColor;\n\
+    \void main()\n\
+    \{\n\
+    \   FragColor = vec4(frag_col.x, frag_col.y, frag_col.z, 1.0f);\n\
+    \}"
+
   val graphLines: Real32.real vector = 
     #[
       (* x = ~0.95 *)

imperative-shell/shell.sml

@@ -16,18 +16,19 @@ struct
       callbackListener mailbox
     end
 
-  fun loop (window, graphDrawObject) =
+  fun loop (window, graphDrawObject, buttonDrawObject) =
     if not (Glfw.windowShouldClose window) then
       let
         val _ = Gles3.clearColor (1.0, 1.0, 1.0, 1.0)
         val _ = Gles3.clear ()
 
         val _ = AppDraw.drawGraphLines graphDrawObject
+        val _ = AppDraw.drawButton (buttonDrawObject, #[])
 
         val _ = Glfw.pollEvents ()
         val _ = Glfw.swapBuffers window
       in
-        loop (window, graphDrawObject)
+        loop (window, graphDrawObject, buttonDrawObject)
       end
     else
       Glfw.terminate ()
@@ -44,6 +45,7 @@ struct
       val _ = Gles3.loadGlad ()
 
       val graphDrawObject = AppDraw.initGraphLines ()
+      val buttonDrawObject = AppDraw.initButton ()
 
       val inputMailbox = Mailbox.mailbox ()
       (* Set callback sender *)
@@ -63,7 +65,7 @@ struct
       (* Set callback listener *)
       val _ = CML.spawn (fn () => callbackListener inputMailbox)
     in
-      loop (window, graphDrawObject)
+      loop (window, graphDrawObject, buttonDrawObject)
     end
 end