Add sample script for the Gtk::GLArea widget

gtk3/sample/misc/gtkglarea1.rb

@@ -0,0 +1,123 @@
+=begin
+  gtkglarea1.rb draw a triangle on a grey background
+  this script need the opengl-bindings gem from :
+  https://github.com/vaiorabbit/ruby-opengl
+
+  gem install opengl-bindings
+
+  sources:
+  http://antongerdelan.net/opengl/hellotriangle.html
+  opengl-bindings/sample/RedBook/varray
+  opengl-bindings/sample/GLES/gles.rb
+  http://www.opengl-tutorial.org/beginners-tutorials/tutorial-2-the-first-triangle/
+  https://developer.gnome.org/gtk3/stable/GtkGLArea.html
+  https://www.bassi.io/articles/2015/02/17/using-opengl-with-gtk/
+  http://stackoverflow.com/questions/30337845/gldrawarrays-not-working-using-gtkglarea-in-gtk3
+  http://gamedev.stackexchange.com/questions/8042/vertex-array-object-opengl
+=end
+
+require "gtk3"
+require "opengl"
+
+unless Gtk::Version.or_later?(3, 16, 0)
+  puts "This sample requires GTK+ 3.16.0 or later: #{Gtk::Version::STRING}"
+  exit
+end
+
+case OpenGL.get_platform
+when :OPENGL_PLATFORM_WINDOWS
+  OpenGL.load_lib("opengl32.dll", "C:/Windows/System32")
+when :OPENGL_PLATFORM_MACOSX
+  OpenGL.load_lib("libGL.dylib", "/System/Library/Frameworks/OpenGL.framework/Libraries")
+when :OPENGL_PLATFORM_LINUX
+  OpenGL.load_lib
+else
+  fail "Unsupported platform."
+end
+
+include OpenGL
+
+window = Gtk::Window.new("OpenGL widget test")
+
+window.set_size_request(400, 400)
+glarea = Gtk::GLArea.new
+
+window.add(glarea)
+
+gl_vao = nil
+
+glarea.signal_connect("realize") do |widget|
+
+  widget.make_current
+
+  # Check can only be done when we have an OpenGL context
+  # https://www.opengl.org/wiki/FAQ#What_is_an_OpenGL_context_and_why_do_you_need_a_window_to_do_GL_rendering.3F
+  # https://www.opengl.org/wiki/FAQ#How_do_I_tell_what_version_of_OpenGL_I.27m_using.3F
+
+  version = glGetString(GL_VERSION).to_s.split(" ").first.split(".").collect(&:to_i)
+  unless version[0] >= 3 && version[1] >= 2
+    puts "Gtk::GLArea widget require an OpenGL version >= 3.2, your version is #{version[0]}.#{version[1]}"
+    exit 1
+  end
+
+  puts "realize"
+  # Define a triangle in a vertex buffer ( Vertex Buffer Object)
+
+  points = [
+    0.0, 0.5, 0.0,  # x1, y1, z1
+    0.5, -0.5, 0.0, # x2, y2, z2
+    -0.5, -0.5, 0.0 # x3, y3, z3
+  ]
+  # Create a vertex array object (VAO) and "bind" it (set it as the current VAO)
+  vao_buf = "    "
+  glGenVertexArrays(1, vao_buf)
+  gl_vao = vao_buf.unpack("L")[0]
+  glBindVertexArray(gl_vao)
+
+  # We copy points onto the graphics card in a unit called vertex buffer object (vbo).
+  # Create an empty buffer
+  vbo_buf = "    "
+  glGenBuffers(1, vbo_buf)
+  g_vbo = vbo_buf.unpack("L")[0]
+  # Set the empty buffer as the current OpenGL's state machine by "binding"
+  glBindBuffer(GL_ARRAY_BUFFER, g_vbo)
+  # Copy the points in the currently bound buffer
+  glBufferData(GL_ARRAY_BUFFER,
+               3 * 4 * Fiddle::SIZEOF_FLOAT,
+               points.pack("F*"),
+               GL_STATIC_DRAW
+              )
+
+  # First attribute buffer : vertices
+  glEnableVertexAttribArray(0)
+  glVertexAttribPointer(0,        # No particular reason for 0
+                        3,        # size
+                        GL_FLOAT, # type
+                        GL_FALSE, # normalized?
+                        0,        # stride
+                        0         # array buffer offset
+                       )
+  # Clear the current VAO
+  glBindVertexArray(0)
+end
+
+glarea.signal_connect("render") do |_widget, _context|
+  puts "render"
+  glClearColor(0.3, 0.3, 0.3, 1)
+  glClear(GL_COLOR_BUFFER_BIT)
+  # Reload the VAO we created previously
+  glBindVertexArray(gl_vao)
+  glDrawArrays(GL_TRIANGLES, 0, 3)
+
+  # we completed our drawing; the draw commands will be
+  # flushed at the end of the signal emission chain, and
+  # the buffers will be drawn on the window
+  true # to stop other handlers from being invoked for the event.
+  # false to propagate the event further.
+end
+
+window.signal_connect("destroy") { Gtk.main_quit }
+
+window.show_all
+
+Gtk.main