add basic imperative shell

shell/gl-draw.sml

@@ -0,0 +1,83 @@
+structure GlDraw =
+struct
+  open CML
+
+  type t = { window: MLton.Pointer.t }
+
+  fun createShader (shaderType, shaderString) =
+    let
+      val shader = Gles3.createShader shaderType
+      val _ = Gles3.shaderSource (shader, shaderString)
+      val _ = Gles3.compileShader shader
+    in
+      shader
+    end
+
+  fun createProgram (vertexShader, fragmentShader) =
+    let
+      val program = Gles3.createProgram ()
+      val _ = Gles3.attachShader (program, vertexShader)
+      val _ = Gles3.attachShader (program, fragmentShader)
+      val _ = Gles3.linkProgram program
+    in
+      program
+    end
+
+  fun create window =
+    let
+      (* create vertex buffer, program, etc. *)
+      val textVertexBuffer = Gles3.createBuffer ()
+      val xyrgbVertexShader = createShader
+        (Gles3.VERTEX_SHADER, GlShaders.xyrgbVertexShaderString)
+
+      val rgbFragmentShader = createShader
+        (Gles3.FRAGMENT_SHADER, GlShaders.rgbFragmentShaderString)
+
+      val placeholderProgram = createProgram (xyrgbVertexShader, rgbFragmentShader)
+    in
+      {window = window}
+    end
+
+  fun drawXyrgb (vertexBuffer, program, drawLength) =
+    if drawLength > 0 then
+      let
+        val _ = Gles3.bindBuffer vertexBuffer
+        (* enable xy component from uploaded array *)
+        val _ = Gles3.vertexAttribPointer (0, 2, 5, 0)
+        val _ = Gles3.enableVertexAttribArray 0
+        (* enable rgb component from uploaded array *)
+        val _ = Gles3.vertexAttribPointer (1, 3, 5, 8)
+        val _ = Gles3.enableVertexAttribArray 1
+
+        val _ = Gles3.useProgram program
+        val _ = Gles3.drawArrays (Gles3.TRIANGLES, 0, drawLength)
+      in
+        ()
+      end
+    else
+      ()
+
+  fun helpLoop (shellState as {window, ...}: t) =
+    case Glfw.windowShouldClose window of
+      false =>
+        let
+          val _ = Gles3.clearColor (1.0, 1.0, 1.0, 1.0)
+          val _ = Gles3.clear ()
+
+          (* todo:
+           * - update game state
+           * - consume draw messages 
+           * - finally, draw 
+           * *)
+          val _ = Glfw.swapBuffers window
+          val _ = Glfw.waitEvents ()
+        in
+          helpLoop shellState
+        end
+    | true => Glfw.terminate ()
+
+  fun loop window =
+    let val shellState = create window
+    in helpLoop shellState
+    end
+end