diff --git a/__init__.py b/__init__.py
index 8ef28dd..a52f73b 100644
--- a/__init__.py
+++ b/__init__.py
@@ -185,7 +185,9 @@ def mat4_mul_mat4(ret, a, b):
 initialize = _lib.rk_initialize
 initialize.restype = ctypes.c_void_p
 initialize.argtypes = (
-    ctypes.c_char_p,) # name
+    ctypes.c_char_p, # name
+    ctypes.c_uint, # width
+    ctypes.c_uint) # height
 
 _load_shader = _lib.rk_load_shader
 _load_shader.restype = ctypes.c_void_p
diff --git a/cpp/opengl/render_context.hpp b/cpp/opengl/render_context.hpp
index 1d632a0..5d44619 100644
--- a/cpp/opengl/render_context.hpp
+++ b/cpp/opengl/render_context.hpp
@@ -13,16 +13,19 @@
 // You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-#ifndef _RK_ENGINE_RENDER_OPENGL_CONTEXT_H
-#define _RK_ENGINE_RENDER_OPENGL_CONTEXT_H
+#ifndef _RK_ENGINE_RENDER_CONTEXT_H
+#define _RK_ENGINE_RENDER_CONTEXT_H
 
 #include "../render.hpp"
+#include <GL/glx.h>
+
+extern PFNGLDRAWELEMENTSINSTANCEDBASEINSTANCEPROC rk_DrawElementsInstancedBaseInstance;
+extern PFNGLMULTIDRAWELEMENTSINDIRECTPROC rk_MultiDrawElementsIndirect;
 
 RK_EXPORT rk_window_t rk_create_context(
     char const * name,
-    int profile,
-    int major,
-    int minor);
+    rk_uint width,
+    rk_uint height);
 
 RK_EXPORT char ** rk_load_shader_source(
     char const * filename,
@@ -35,4 +38,4 @@ RK_EXPORT void rk_free_shader_source(
 RK_EXPORT void rk_swap_buffers();
 RK_EXPORT void rk_destroy_context();
 
-#endif // _RK_ENGINE_RENDER_OPENGL_CONTEXT_H
+#endif // _RK_ENGINE_RENDER_CONTEXT_H
diff --git a/cpp/opengl/render_context_glx.cpp b/cpp/opengl/render_context_glx.cpp
index 884ecd1..93ddba0 100644
--- a/cpp/opengl/render_context_glx.cpp
+++ b/cpp/opengl/render_context_glx.cpp
@@ -18,7 +18,7 @@
 #include "render_context.hpp"
 #include <cstdio>
 #include <cstring>
-#include <GL/glx.h>
+#include <GLES3/gl32.h>
 #include <X11/Xlib.h>
 
 static Display * rk_display = nullptr;
@@ -31,6 +31,31 @@ static bool rk_error_occured = false;
 #define GLX_CONTEXT_MINOR_VERSION_ARB 0x2092
 typedef GLXContext (*glXCreateContextAttribsARBProc)(Display *, GLXFBConfig, GLXContext, Bool, int const *);
 
+PFNGLDRAWELEMENTSINSTANCEDBASEINSTANCEPROC rk_DrawElementsInstancedBaseInstance = nullptr;
+PFNGLMULTIDRAWELEMENTSINDIRECTPROC rk_MultiDrawElementsIndirect = nullptr;
+
+static int const rk_visual_attribs[] = {
+    GLX_X_RENDERABLE, True,
+    GLX_DRAWABLE_TYPE, GLX_WINDOW_BIT,
+    GLX_RENDER_TYPE, GLX_RGBA_BIT,
+    GLX_X_VISUAL_TYPE, GLX_TRUE_COLOR,
+    GLX_RED_SIZE, 8,
+    GLX_GREEN_SIZE, 8,
+    GLX_BLUE_SIZE, 8,
+    GLX_ALPHA_SIZE, 8,
+    GLX_DEPTH_SIZE, 24,
+    GLX_STENCIL_SIZE, 8,
+    GLX_DOUBLEBUFFER, True,
+    None
+};
+
+static int const rk_context_attribs[] = {
+    GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
+    GLX_CONTEXT_MINOR_VERSION_ARB, 2,
+    GLX_CONTEXT_PROFILE_MASK_ARB, GLX_CONTEXT_ES_PROFILE_BIT_EXT,
+    None
+};
+
 static void rk_printf(
     char const * messsage) {
     printf("[GLX] %s\n", messsage);
@@ -66,30 +91,14 @@ static int rk_error_handler(
 
 rk_window_t rk_create_context(
     char const * name,
-    int profile,
-    int major,
-    int minor) {
+    rk_uint width,
+    rk_uint height) {
     rk_display = XOpenDisplay(nullptr);
     if (!rk_display) {
         rk_printf("Failed to open X display.");
         return nullptr;
     }
 
-    static int const visual_attribs[] = {
-        GLX_X_RENDERABLE, True,
-        GLX_DRAWABLE_TYPE, GLX_WINDOW_BIT,
-        GLX_RENDER_TYPE, GLX_RGBA_BIT,
-        GLX_X_VISUAL_TYPE, GLX_TRUE_COLOR,
-        GLX_RED_SIZE, 8,
-        GLX_GREEN_SIZE, 8,
-        GLX_BLUE_SIZE, 8,
-        GLX_ALPHA_SIZE, 8,
-        GLX_DEPTH_SIZE, 24,
-        GLX_STENCIL_SIZE, 8,
-        GLX_DOUBLEBUFFER, True,
-        None
-    };
-
     int glx_major, glx_minor;
     if (!glXQueryVersion(rk_display, &glx_major, &glx_minor) || (glx_major == 1 && glx_minor < 3) || glx_major < 1) {
         rk_printf("Invalid GLX version.");
@@ -98,7 +107,7 @@ rk_window_t rk_create_context(
     }
 
     int fbcount;
-    GLXFBConfig * const fbc = glXChooseFBConfig(rk_display, DefaultScreen(rk_display), visual_attribs, &fbcount);
+    GLXFBConfig * const fbc = glXChooseFBConfig(rk_display, DefaultScreen(rk_display), rk_visual_attribs, &fbcount);
     if (!fbc) {
         rk_printf("Failed to retrieve a framebuffer config.");
         rk_destroy_context();
@@ -141,7 +150,7 @@ rk_window_t rk_create_context(
     swa.border_pixel = 0;
     swa.event_mask = StructureNotifyMask;
     rk_window = XCreateWindow(rk_display, RootWindow(rk_display, vi->screen),
-                                0, 0, 1600, 900, 0, vi->depth, InputOutput, vi->visual,
+                                0, 0, width, height, 0, vi->depth, InputOutput, vi->visual,
                                 CWBorderPixel | CWColormap | CWEventMask, &swa);
     if (!rk_window) {
         rk_printf("Failed to create window.");
@@ -150,27 +159,21 @@ rk_window_t rk_create_context(
     }
     XFree(vi);
     XStoreName(rk_display, rk_window, name);
-    XMapWindow( rk_display, rk_window );
+    XMapWindow(rk_display, rk_window);
 
     char const * const glxExts = glXQueryExtensionsString(rk_display, DefaultScreen(rk_display));
-    glXCreateContextAttribsARBProc glXCreateContextAttribsARB = 0;
-    glXCreateContextAttribsARB = (glXCreateContextAttribsARBProc)
-        glXGetProcAddressARB((const GLubyte *)("glXCreateContextAttribsARB"));
+    glXCreateContextAttribsARBProc const glXCreateContextAttribsARB =
+        reinterpret_cast<glXCreateContextAttribsARBProc>(
+            glXGetProcAddressARB(reinterpret_cast<const GLubyte *>("glXCreateContextAttribsARB")));
 
     rk_error_occured = false;
     int (*oldHandler)(Display *, XErrorEvent *) = XSetErrorHandler(&rk_error_handler);
     if (!rk_extension_supported(glxExts, "GLX_ARB_create_context") || !glXCreateContextAttribsARB) {
-        rk_printf("glXCreateContextAttribsARB() not found.");
+        rk_printf("glXCreateContextAttribsARB() extension not found.");
         rk_destroy_context();
         return nullptr;
     } else {
-        const int context_attribs[] = {
-            GLX_CONTEXT_MAJOR_VERSION_ARB, major,
-            GLX_CONTEXT_MINOR_VERSION_ARB, minor,
-            GLX_CONTEXT_PROFILE_MASK_ARB, profile,
-            None
-        };
-        rk_context = glXCreateContextAttribsARB(rk_display, bestFbc, 0, True, context_attribs);
+        rk_context = glXCreateContextAttribsARB(rk_display, bestFbc, 0, True, rk_context_attribs);
         XSync(rk_display, False);
         if (rk_error_occured || !rk_context) {
             rk_printf("Failed to create context.");
@@ -184,6 +187,24 @@ rk_window_t rk_create_context(
         rk_printf("Warning: Rendering context is indirect.");
     }
     glXMakeCurrent(rk_display, rk_window, rk_context);
+
+    if (rk_extension_supported(glxExts, "GL_EXT_base_instance")) {
+        rk_DrawElementsInstancedBaseInstance =
+            reinterpret_cast<PFNGLDRAWELEMENTSINSTANCEDBASEINSTANCEPROC>(
+                glXGetProcAddressARB(reinterpret_cast<const GLubyte *>("DrawElementsInstancedBaseInstance")));
+        if (rk_DrawElementsInstancedBaseInstance) {
+            rk_printf("Using extension GL_EXT_base_instance::DrawElementsInstancedBaseInstance.");
+            if (rk_extension_supported(glxExts, "GL_EXT_multi_draw_indirect")) {
+                rk_MultiDrawElementsIndirect =
+                    reinterpret_cast<PFNGLMULTIDRAWELEMENTSINDIRECTPROC>(
+                        glXGetProcAddressARB(reinterpret_cast<const GLubyte *>("MultiDrawElementsIndirectEXT")));
+                if (rk_MultiDrawElementsIndirect) {
+                    rk_printf("Using extension GL_EXT_multi_draw_indirect::MultiDrawElementsIndirectEXT.");
+                }
+            }
+        }
+    }
+
     return reinterpret_cast<rk_window_t>(rk_window);
 }
 
diff --git a/cpp/opengl/render_opengles.cpp b/cpp/opengl/render_opengles.cpp
index 23e0830..b5ea8f7 100644
--- a/cpp/opengl/render_opengles.cpp
+++ b/cpp/opengl/render_opengles.cpp
@@ -15,18 +15,11 @@
 
 #include "render_opengles.hpp"
 #include <cstdio>
-#include <cstring>
-
-//TODO: move the GLX stuff to render_context_glx.cpp
-#include <GL/glx.h>
 
 static rk_shader const * rk_current_shader = nullptr;
 static rk_vertices const * rk_current_vertices = nullptr;
 static bool rk_frame = false;
 
-static PFNGLDRAWELEMENTSINSTANCEDBASEINSTANCEPROC rk_DrawElementsInstancedBaseInstance = nullptr;
-static PFNGLMULTIDRAWELEMENTSINDIRECTPROC rk_MultiDrawElementsIndirect = nullptr;
-
 static void rk_printf(char const * messsage) {
     printf("[RK_ENGINE] %s\n", messsage);
 }
@@ -47,26 +40,11 @@ static void rk_debug_message_callback(
     printf("[RK_ENGINE][GL] (id=%d) %s\n", id, message);
 }
 
-static __GLXextFuncPtr rk_extension(
-    char const * const name,
-    char const * const func) {
-    __GLXextFuncPtr ext_ptr = nullptr;
-    GLint num_exts = 0;
-    glGetIntegerv(GL_NUM_EXTENSIONS, &num_exts);
-    for (int ext_index = 0; ext_index < num_exts; ++ext_index) {
-        char const * const ext_name = reinterpret_cast<char const *>(glGetStringi(GL_EXTENSIONS, ext_index));
-        if (strcmp(name, ext_name) == 0) {
-            ext_ptr = glXGetProcAddressARB(reinterpret_cast<GLubyte const *>(func));
-            printf("[RK_ENGINE] Using extension %s::%s\n", name, func);
-            break;
-        }
-    }
-    return ext_ptr;
-}
-
 rk_window_t rk_initialize(
-    char const * name) {
-    rk_window_t const window = rk_create_context(name, GLX_CONTEXT_ES_PROFILE_BIT_EXT, 3, 2);
+    char const * name,
+    rk_uint width,
+    rk_uint height) {
+    rk_window_t const window = rk_create_context(name, width, height);
     if (window) {
         GLubyte const * const vendor = glGetString(GL_VENDOR);
         GLubyte const * const renderer = glGetString(GL_RENDERER);
@@ -75,15 +53,6 @@ rk_window_t rk_initialize(
         GLubyte const * const language = glGetString(GL_SHADING_LANGUAGE_VERSION);
         printf("[RK_ENGINE] version: %s, language: %s\n", version, language);
 
-        rk_DrawElementsInstancedBaseInstance =
-            reinterpret_cast<PFNGLDRAWELEMENTSINSTANCEDBASEINSTANCEPROC>(
-                rk_extension("GL_EXT_base_instance", "DrawElementsInstancedBaseInstance"));
-        if (rk_DrawElementsInstancedBaseInstance) {
-            rk_MultiDrawElementsIndirect =
-                reinterpret_cast<PFNGLMULTIDRAWELEMENTSINDIRECTPROC>(
-                    rk_extension("GL_EXT_multi_draw_indirect", "MultiDrawElementsIndirectEXT"));
-        }
-
         GLint context_flags = 0;
         glGetIntegerv(GL_CONTEXT_FLAGS, &context_flags);
         if (context_flags & GL_CONTEXT_FLAG_DEBUG_BIT) {
diff --git a/cpp/render.hpp b/cpp/render.hpp
index 6f22d48..4dbeb1d 100644
--- a/cpp/render.hpp
+++ b/cpp/render.hpp
@@ -99,7 +99,9 @@ union rk_mesh {
 };
 
 RK_EXPORT rk_window_t rk_initialize(
-    char const * name);
+    char const * name,
+    rk_uint width,
+    rk_uint height);
 
 RK_EXPORT rk_shader_t rk_load_shader(
     char const * name);