add draw module (very incomplete)

shell/gl-draw.sml

@@ -0,0 +1,50 @@
+structure GlDraw =
+struct
+  (* The name doesn't make it clear, but this structure
+   * couples GLFW and OpenGL.
+   * I'm not sure if I will use native windowing systems
+   * or other graphics APIs at a later stage,
+   * but the current priority is GLFW + OpenGL. 
+   * *)
+  type t =
+    { textVertexBuffer: Word32.word
+    , textProgram: Word32.word
+    , textDrawLength: int
+    , window: MLton.Pointer.t
+    }
+
+  fun createShader (shaderType, shaderString) =
+    let
+      val shader = Gles3.createShader Gles3.VERTEX_SHADER
+      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 () =
+    let
+      (* Set up GLFW. *)
+      val _ = Glfw.init ()
+      val _ = Glfw.windowHint (Glfw.CONTEXT_VERSION_MAJOR (), 3)
+      val _ = Glfw.windowHint (Glfw.DEPRECATED (), Glfw.FALSE ())
+      val _ = Glfw.windowHint (Glfw.SAMPLES (), 4)
+      val window = Glfw.createWindow (1600, 900, "shf")
+      val _ = Glfw.makeContextCurrent window
+      val _ = Gles3.loadGlad ()
+
+    (* todo: create vertex buffer, program, etc. for text. *)
+    in
+      {window = window}
+    end
+end

shf.mlb

@@ -15,4 +15,5 @@ in
 end
 
 shell/gl-shaders.sml
+shell/gl-draw.sml
 shell/shell.sml