[skip ci] basic startup for opengl & working example

cmake/TaichiCore.cmake

@@ -88,6 +88,10 @@ if (TI_WITH_CUDA)
     target_link_libraries(${LIBRARY_NAME} ${llvm_ptx_libs})
 endif()
 
+#target_link_libraries(${LIBRARY_NAME} /usr/lib/libGL.so GL)
+target_link_libraries(${LIBRARY_NAME} /usr/lib/libGLEW.so GLEW)
+target_link_libraries(${LIBRARY_NAME} /usr/lib/libglfw.so glfw)
+
 # add_executable(runtime runtime/runtime.cpp)
 
 # Optional dependencies

examples/opengl_backend.py

@@ -0,0 +1,12 @@
+import taichi as ti
+
+ti.init(arch=ti.opengl)
+
+x = ti.var(ti.f32, shape=())
+x[None] = 1
+
+@ti.kernel
+def func():
+  x[None] = x[None] * 2
+
+func()

python/taichi/lang/__init__.py

@@ -27,6 +27,7 @@
 x86_64 = core.x86_64
 cuda = core.cuda
 metal = core.metal
+opengl = core.opengl
 profiler_print = lambda: core.get_current_program().profiler_print()
 profiler_clear = lambda: core.get_current_program().profiler_clear()
 
@@ -178,6 +179,8 @@ def supported_archs():
     archs.append(cuda)
   if ti.core.with_metal():
     archs.append(metal)
+  if ti.core.with_opengl():
+    archs.append(opengl)
   return archs
 
 class _ArchCheckers(object):