8 files changed, 583 insertions, 71 deletions

diff --git a/common/curl_request.cpp b/common/curl_request.cpp
new file mode 100644
index 0000000000..3370c0a859
--- /dev/null
+++ b/common/curl_request.cpp
@@ -0,0 +1,383 @@
+
+#include <mbgl/platform/platform.hpp>
+#include <mbgl/platform/request.hpp>
+#include <mbgl/util/uv_detail.hpp>
+#include <mbgl/util/std.hpp>
+
+#include <queue>
+#include <boost/lockfree/queue.hpp>
+
+#include <curl/curl.h>
+
+// This file contains code from http://curl.haxx.se/libcurl/c/multi-uv.html:
+
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 1998 - 2013, Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at http://curl.haxx.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+
+/* Example application code using the multi socket interface to download
+   multiple files at once, but instead of using curl_multi_perform and
+   curl_multi_wait, which uses select(), we use libuv.
+   It supports epoll, kqueue, etc. on unixes and fast IO completion ports on
+   Windows, which means, it should be very fast on all platforms..
+
+   Written by Clemens Gruber, based on an outdated example from uvbook and
+   some tests from libuv.
+
+   Requires libuv and (of course) libcurl.
+
+   See http://nikhilm.github.com/uvbook/ for more information on libuv.
+*/
+
+namespace mbgl {
+namespace platform {
+namespace request {
+
+struct curl_context {
+    uv_poll_t poll_handle;
+    curl_socket_t sockfd;
+};
+
+// Handles the request thread + messaging to the thread.
+static uv_thread_t thread;
+static uv::once init_thread_once;
+static uv_loop_t *loop = nullptr;
+static uv_async_t async_add;
+static uv_async_t async_cancel;
+
+// Stores pointers (!) to shared_ptrs. We use shared_ptrs so that request objects don't get
+// auto-destructed while they're in progress. The TileData object retains a weak_ptr to this
+// request, so we have to use a shared_ptr here to ensure that this object stays alive.
+static boost::lockfree::queue<std::shared_ptr<mbgl::platform::Request> *> add_queue(8);
+static boost::lockfree::queue<std::shared_ptr<mbgl::platform::Request> *> cancel_queue(8);
+
+// Used as the CURL timer function to periodically check for socket updates.
+static uv_timer_t timeout;
+
+// CURL multi handle that we use to request multiple URLs at the same time, without having to block
+// and spawn threads.
+static CURLM *curl_multi = nullptr;
+
+// CURL share handles are used for sharing session state (e.g.)
+static uv::mutex curl_share_mutex;
+static CURLSH *curl_share = nullptr;
+
+// A queue that we use for storing resuable CURL easy handles to avoid creating and destroying them
+// all the time.
+static std::queue<CURL *> curl_handle_cache;
+
+
+class CURLRequest : public mbgl::platform::Request {
+public:
+    CURLRequest(const std::string &url,
+                std::function<void(mbgl::platform::Response *)> callback,
+                std::shared_ptr<uv::loop> loop)
+        : Request(url, callback, loop) {}
+
+    CURL *curl = nullptr;
+};
+
+
+// Implementation starts here.
+
+// Locks the CURL share handle
+void curl_share_lock(CURL *, curl_lock_data, curl_lock_access, void *) { curl_share_mutex.lock(); }
+
+// Unlocks the CURL share handle
+void curl_share_unlock(CURL *, curl_lock_data, void *) { curl_share_mutex.unlock(); }
+
+curl_context *create_curl_context(curl_socket_t sockfd) {
+    curl_context *context = new curl_context;
+    context->sockfd = sockfd;
+
+    uv_poll_init_socket(loop, &context->poll_handle, sockfd);
+    context->poll_handle.data = context;
+
+    return context;
+}
+
+void curl_close_cb(uv_handle_t *handle) {
+    curl_context *context = (curl_context *)handle->data;
+    free(context);
+}
+
+void destroy_curl_context(curl_context *context) {
+    uv_close((uv_handle_t *)&context->poll_handle, curl_close_cb);
+}
+
+void remove_curl_handle(CURL *handle) {
+    CURLMcode error = curl_multi_remove_handle(curl_multi, handle);
+    if (error != CURLM_OK) {
+        throw std::runtime_error(std::string("CURL multi error: ") + curl_multi_strerror(error));
+    }
+
+    curl_easy_reset(handle);
+    curl_handle_cache.push(handle);
+}
+
+void curl_perform(uv_poll_t *req, int /*status*/, int events) {
+    int running_handles;
+    int flags = 0;
+    curl_context *context;
+    CURLMsg *message;
+    int pending;
+
+    uv_timer_stop(&timeout);
+
+    if (events & UV_READABLE)
+        flags |= CURL_CSELECT_IN;
+    if (events & UV_WRITABLE)
+        flags |= CURL_CSELECT_OUT;
+
+    context = (curl_context *)req;
+
+    curl_multi_socket_action(curl_multi, context->sockfd, flags, &running_handles);
+
+    while ((message = curl_multi_info_read(curl_multi, &pending))) {
+        switch (message->msg) {
+        case CURLMSG_DONE: {
+            std::shared_ptr<Request> *req = nullptr;
+            curl_easy_getinfo(message->easy_handle, CURLINFO_PRIVATE, (char *)&req);
+
+            // Add human-readable error code
+            if (message->data.result != CURLE_OK) {
+                (*req)->res->error_message = curl_easy_strerror(message->data.result);
+                (*req)->res->code = -1;
+            } else {
+                curl_easy_getinfo(message->easy_handle, CURLINFO_RESPONSE_CODE, &(*req)->res->code);
+            }
+
+            // We're currently in the CURL request thread. We're going to schedule a uv_work request
+            // that executes the background function in a threadpool, and tell it to call the
+            // after callback back in the main uv loop.
+            (*req)->complete();
+
+            CURL *handle = message->easy_handle;
+            remove_curl_handle(handle);
+
+            // We're setting this to NULL because there might still be shared_ptrs around that could
+            // be cancelled.
+            ((CURLRequest *)req->get())->curl = nullptr;
+
+            // Delete the shared_ptr pointer we created earlier.
+            delete req;
+            break;
+        }
+
+        default:
+            // This should never happen, because there are no other message types.
+            throw std::runtime_error("CURLMSG returned unknown message type");
+        }
+    }
+}
+
+int handle_socket(CURL * /*easy*/, curl_socket_t s, int action, void * /*userp*/, void *socketp) {
+    curl_context *context = nullptr;
+
+    if (socketp) {
+        context = (curl_context *)socketp;
+    } else if (action != CURL_POLL_REMOVE) {
+        context = create_curl_context(s);
+    }
+
+    if (context) {
+        curl_multi_assign(curl_multi, s, (void *)context);
+        if (action == CURL_POLL_IN || action == CURL_POLL_INOUT) {
+            uv_poll_start(&context->poll_handle, UV_READABLE, curl_perform);
+        }
+        if (action == CURL_POLL_OUT || action == CURL_POLL_INOUT) {
+            uv_poll_start(&context->poll_handle, UV_WRITABLE, curl_perform);
+        }
+        if (action == CURL_POLL_REMOVE && socketp) {
+            uv_poll_stop(&context->poll_handle);
+            destroy_curl_context(context);
+            curl_multi_assign(curl_multi, s, NULL);
+        }
+    }
+
+    return 0;
+}
+
+void on_timeout(uv_timer_t *, int status /*req*/) {
+    int running_handles;
+    CURLMcode error =
+        curl_multi_socket_action(curl_multi, CURL_SOCKET_TIMEOUT, 0, &running_handles);
+    if (error != CURLM_OK) {
+        throw std::runtime_error(std::string("CURL multi error: ") + curl_multi_strerror(error));
+    }
+}
+
+void start_timeout(CURLM * /*multi*/, long timeout_ms, void * /*userp*/) {
+    if (timeout_ms <= 0) {
+        on_timeout(&timeout, -1);
+    } else {
+        uv_timer_start(&timeout, &on_timeout, timeout_ms, 0);
+    }
+}
+
+// This function is the first function called in the request thread. It sets up the CURL share/multi
+// handles and runs the thread loop.
+void thread_init(void * /*ptr*/) {
+    uv_timer_init(loop, &timeout);
+
+    CURLSHcode share_error;
+    curl_share = curl_share_init();
+
+    share_error = curl_share_setopt(curl_share, CURLSHOPT_LOCKFUNC, curl_share_lock);
+    if (share_error != CURLSHE_OK) {
+        throw std::runtime_error(std::string("CURL share error: ") + curl_share_strerror(share_error));
+    }
+
+    share_error = curl_share_setopt(curl_share, CURLSHOPT_UNLOCKFUNC, curl_share_unlock);
+    if (share_error != CURLSHE_OK) {
+        throw std::runtime_error(std::string("CURL share error: ") + curl_share_strerror(share_error));
+    }
+
+    CURLMcode multi_error;
+    curl_multi = curl_multi_init();
+
+    multi_error = curl_multi_setopt(curl_multi, CURLMOPT_SOCKETFUNCTION, handle_socket);
+    if (multi_error != CURLM_OK) {
+        throw std::runtime_error(std::string("CURL multi error: ") + curl_multi_strerror(multi_error));
+    }
+    multi_error = curl_multi_setopt(curl_multi, CURLMOPT_TIMERFUNCTION, start_timeout);
+    if (multi_error != CURLM_OK) {
+        throw std::runtime_error(std::string("CURL multi error: ") + curl_multi_strerror(multi_error));
+
+    }
+
+    // Main event loop. This will not return until the request loop is terminated.
+    uv_run(loop, UV_RUN_DEFAULT);
+
+    curl_multi_cleanup(curl_multi);
+    curl_multi = nullptr;
+    curl_share_cleanup(curl_share);
+    curl_share = nullptr;
+
+    // Clean up all the CURL easy handles that we kept around for potential future reuse.
+    while (!curl_handle_cache.empty()) {
+        curl_easy_cleanup(curl_handle_cache.front());
+        curl_handle_cache.pop();
+    }
+}
+
+// This function is called when we have new data for a request. We just append it to the string
+// containing the previous data.
+size_t curl_write_cb(void *contents, size_t size, size_t nmemb, void *userp) {
+    ((std::string *)userp)->append((char *)contents, size * nmemb);
+    return size * nmemb;
+}
+
+// This callback is called in the request event loop (on the request thread).
+// It initializes newly queued up download requests and adds them to the CURL
+// multi handle.
+void async_add_cb(uv_async_t *, int status /*async*/) {
+    std::shared_ptr<Request> *req = nullptr;
+    while (add_queue.pop(req)) {
+        // Make sure that we're not starting requests that have been cancelled
+        // already by async_cancel_cb.
+        if ((*req)->cancelled) {
+            delete req;
+            continue;
+        }
+
+        // Obtain a curl handle (and try to reuse existing handles before creating new ones).
+        CURL *handle = nullptr;
+        if (!curl_handle_cache.empty()) {
+            handle = curl_handle_cache.front();
+            curl_handle_cache.pop();
+        } else {
+            handle = curl_easy_init();
+        }
+
+        ((CURLRequest *)req->get())->curl = handle;
+
+        curl_easy_setopt(handle, CURLOPT_PRIVATE, req);
+        curl_easy_setopt(handle, CURLOPT_CAINFO, "ca-bundle.crt");
+        curl_easy_setopt(handle, CURLOPT_URL, (*req)->url.c_str());
+        curl_easy_setopt(handle, CURLOPT_WRITEFUNCTION, curl_write_cb);
+        curl_easy_setopt(handle, CURLOPT_WRITEDATA, &(*req)->res->body);
+        curl_easy_setopt(handle, CURLOPT_ACCEPT_ENCODING, "gzip, deflate");
+        curl_easy_setopt(handle, CURLOPT_SHARE, curl_share);
+        curl_multi_add_handle(curl_multi, handle);
+    }
+}
+
+void async_cancel_cb(uv_async_t *, int status /*async*/) {
+    std::shared_ptr<Request> *req = nullptr;
+    while (cancel_queue.pop(req)) {
+        // It is possible that the request has not yet been started, but that it already has been
+        // added to the queue for scheduling new requests. In this case, the CURL handle is invalid
+        // and we manually mark the Request as cancelled.
+        CURL *handle = ((CURLRequest *)req->get())->curl;
+        if (handle && !(*req)->cancelled) {
+            remove_curl_handle(handle);
+            ((CURLRequest *)req->get())->curl = nullptr;
+        }
+        (*req)->cancelled = true;
+
+        delete req;
+        req = nullptr;
+    }
+}
+
+void thread_init_cb() {
+    curl_global_init(CURL_GLOBAL_ALL);
+
+    loop = uv_loop_new();
+    uv_async_init(loop, &async_add, &async_add_cb);
+    uv_async_init(loop, &async_cancel, &async_cancel_cb);
+    uv_thread_create(&thread, thread_init, nullptr);
+}
+} // end namespace request
+} // end namespace platform
+
+
+std::shared_ptr<platform::Request>
+platform::request_http(const std::string &url,
+                       std::function<void(Response *)> callback,
+                       std::shared_ptr<uv::loop> loop) {
+    using namespace request;
+    init_thread_once(thread_init_cb);
+    std::shared_ptr<CURLRequest> req = std::make_shared<CURLRequest>(url, callback, loop);
+
+    // Note that we are creating a new shared_ptr pointer(!) because the lockless queue can't store
+    // objects with nontrivial destructors. We have to make absolutely sure that we manually delete
+    // the shared_ptr when we pop it from the queue.
+    add_queue.push(new std::shared_ptr<Request>(req));
+    uv_async_send(&async_add);
+
+    return req;
+}
+
+// Cancels an HTTP request.
+void platform::cancel_request_http(const std::shared_ptr<Request> &req) {
+    if (req) {
+        using namespace request;
+
+        // Note that we are creating a new shared_ptr pointer(!) because the lockless queue can't
+        // store objects with nontrivial destructors. We have to make absolutely shure that we
+        // manually delete the shared_ptr when we pop it from the queue.
+        cancel_queue.push(new std::shared_ptr<Request>(req));
+        uv_async_send(&async_cancel);
+    }
+}
+} // end namespace mbgl
diff --git a/common/glfw_view.cpp b/common/glfw_view.cpp
index edfb3a6a6f..120faf4df1 100644
--- a/common/glfw_view.cpp
+++ b/common/glfw_view.cpp
@@ -8,7 +8,10 @@ GLFWView::GLFWView(bool fullscreen) : fullscreen(fullscreen) {
 #endif
 }
 
-GLFWView::~GLFWView() { glfwTerminate(); }
+GLFWView::~GLFWView() {
+    map->terminate();
+    glfwTerminate();
+}
 
 void GLFWView::initialize(mbgl::Map *map) {
     View::initialize(map);
@@ -194,6 +197,10 @@ void GLFWView::make_active() {
     glfwMakeContextCurrent(window);
 }
 
+void GLFWView::make_inactive() {
+    glfwMakeContextCurrent(nullptr);
+}
+
 void GLFWView::notify() {
     glfwPostEmptyEvent();
 }
diff --git a/common/glfw_view.hpp b/common/glfw_view.hpp
index 481b1598bb..6e91c1125e 100644
--- a/common/glfw_view.hpp
+++ b/common/glfw_view.hpp
@@ -17,6 +17,7 @@ public:
     void initialize(mbgl::Map *map);
     void swap();
     void make_active();
+    void make_inactive();
     void notify();
     void notify_map_change(mbgl::MapChange change, mbgl::timestamp delay = 0);
 
diff --git a/common/glx.h b/common/glx.h
new file mode 100644
index 0000000000..6b7d9a3df9
--- /dev/null
+++ b/common/glx.h
@@ -0,0 +1,2 @@
+#include <GL/glx.h>
+#undef None
diff --git a/common/headless_display.cpp b/common/headless_display.cpp
new file mode 100644
index 0000000000..bbb1c10f51
--- /dev/null
+++ b/common/headless_display.cpp
@@ -0,0 +1,69 @@
+#include "headless_display.hpp"
+
+#include <stdexcept>
+
+namespace mbgl {
+
+HeadlessDisplay::HeadlessDisplay() {
+#if MBGL_USE_CGL
+    // TODO: test if OpenGL 4.1 with GL_ARB_ES2_compatibility is supported
+    // If it is, use kCGLOGLPVersion_3_2_Core and enable that extension.
+    CGLPixelFormatAttribute attributes[] = {
+        kCGLPFAOpenGLProfile,
+        (CGLPixelFormatAttribute) kCGLOGLPVersion_Legacy,
+        kCGLPFAAccelerated,
+        (CGLPixelFormatAttribute) 0
+    };
+
+    GLint num;
+    CGLError error = CGLChoosePixelFormat(attributes, &pixelFormat, &num);
+    if (error) {
+        fprintf(stderr, "Error pixel format: %s\n", CGLErrorString(error));
+        return;
+    }
+#endif
+
+#if MBGL_USE_GLX
+    if (!XInitThreads()) {
+        throw std::runtime_error("Failed to XInitThreads");
+    }
+    
+    x_display = XOpenDisplay(0);
+
+    if (x_display == nullptr) {
+        throw std::runtime_error("Failed to open X display");
+    }
+
+    static int pixelFormat[] = {
+        GLX_RGBA,
+        GLX_DOUBLEBUFFER,
+        GLX_RED_SIZE, 8,
+        GLX_GREEN_SIZE, 8,
+        GLX_BLUE_SIZE, 8,
+        GLX_ALPHA_SIZE, 8,
+        GLX_DEPTH_SIZE, 24,
+        GLX_STENCIL_SIZE, 8,
+        0
+    };
+
+    x_info = glXChooseVisual(x_display, DefaultScreen(x_display), pixelFormat);
+
+    if (x_info == nullptr) {
+        throw std::runtime_error("Error pixel format");
+    }
+#endif
+}
+
+HeadlessDisplay::~HeadlessDisplay() {
+#if MBGL_USE_CGL
+    CGLDestroyPixelFormat(pixelFormat);
+#endif
+
+#if MBGL_USE_GLX
+    XFree(x_info);
+    XCloseDisplay(x_display);
+#endif
+}
+
+}
+
diff --git a/common/headless_display.hpp b/common/headless_display.hpp
new file mode 100644
index 0000000000..0eb41911ee
--- /dev/null
+++ b/common/headless_display.hpp
@@ -0,0 +1,25 @@
+#ifndef MBGL_COMMON_HEADLESS_DISPLAY
+#define MBGL_COMMON_HEADLESS_DISPLAY
+
+#include "headless_view.hpp"
+
+namespace mbgl {
+
+class HeadlessDisplay {
+public:
+    HeadlessDisplay();
+    ~HeadlessDisplay();
+
+#if MBGL_USE_CGL
+    CGLPixelFormatObj pixelFormat;
+#endif
+
+#if MBGL_USE_GLX
+    Display *x_display = nullptr;
+    XVisualInfo *x_info = nullptr;
+#endif
+};
+
+}
+
+#endif
diff --git a/common/headless_view.cpp b/common/headless_view.cpp
index ace41d38c0..c2084ac90d 100644
--- a/common/headless_view.cpp
+++ b/common/headless_view.cpp
@@ -1,61 +1,38 @@
 #include "headless_view.hpp"
-#include <mbgl/util/timer.hpp>
+#include "headless_display.hpp"
 
 #include <stdexcept>
+#include <sstream>
+#include <string>
 
 namespace mbgl {
 
-HeadlessView::HeadlessView() {
+HeadlessView::HeadlessView()
+    : display_(std::make_shared<HeadlessDisplay>()) {
+    createContext();
+}
+
+HeadlessView::HeadlessView(std::shared_ptr<HeadlessDisplay> display)
+    : display_(display) {
+    createContext();
+}
+
+void HeadlessView::createContext() {
 #if MBGL_USE_CGL
-    // TODO: test if OpenGL 4.1 with GL_ARB_ES2_compatibility is supported
-    // If it is, use kCGLOGLPVersion_3_2_Core and enable that extension.
-    CGLPixelFormatAttribute attributes[] = {
-        kCGLPFAOpenGLProfile,
-        (CGLPixelFormatAttribute) kCGLOGLPVersion_Legacy,
-        kCGLPFAAccelerated,
-        (CGLPixelFormatAttribute) 0
-    };
-
-    CGLPixelFormatObj pixelFormat;
-    GLint num;
-    CGLError error = CGLChoosePixelFormat(attributes, &pixelFormat, &num);
+    CGLError error = CGLCreateContext(display_->pixelFormat, NULL, &gl_context);
     if (error) {
-        fprintf(stderr, "Error pixel format\n");
-        return;
+        throw std::runtime_error("Error creating GL context object\n");
     }
 
-    error = CGLCreateContext(pixelFormat, NULL, &gl_context);
-    CGLDestroyPixelFormat(pixelFormat);
-    if (error) {
-        fprintf(stderr, "Error creating GL context object\n");
-        return;
+    error = CGLEnable(gl_context, kCGLCEMPEngine);
+    if (error != kCGLNoError ) {
+        throw std::runtime_error("Error enabling OpenGL multithreading\n");
     }
 #endif
 
 #if MBGL_USE_GLX
-    x_display = XOpenDisplay(0);
-
-    if (x_display == nullptr) {
-        throw std::runtime_error("Failed to open X display");
-    }
-
-    static int pixelFormat[] = {
-        GLX_RGBA,
-        GLX_DOUBLEBUFFER,
-        GLX_RED_SIZE, 8,
-        GLX_GREEN_SIZE, 8,
-        GLX_BLUE_SIZE, 8,
-        GLX_ALPHA_SIZE, 8,
-        GLX_DEPTH_SIZE, 24,
-        GLX_STENCIL_SIZE, 8,
-        None
-    };
-
-    x_info = glXChooseVisual(x_display, DefaultScreen(x_display), pixelFormat);
-
-    if (x_info == nullptr) {
-        throw std::runtime_error("Error pixel format");
-    }
+    x_display = display_->x_display;
+    x_info = display_->x_info;
 
     gl_context = glXCreateContext(x_display, x_info, 0, GL_TRUE);
     if (gl_context == nullptr) {
@@ -64,12 +41,15 @@ HeadlessView::HeadlessView() {
 #endif
 }
 
-
 void HeadlessView::resize(uint16_t width, uint16_t height, float pixelRatio) {
     clear_buffers();
 
-    width *= pixelRatio;
-    height *= pixelRatio;
+    width_ = width;
+    height_ = height;
+    pixelRatio_ = pixelRatio;
+
+    const unsigned int w = width_ * pixelRatio_;
+    const unsigned int h = height_ * pixelRatio_;
 
 #if MBGL_USE_CGL
     make_active();
@@ -77,12 +57,12 @@ void HeadlessView::resize(uint16_t width, uint16_t height, float pixelRatio) {
     // Create depth/stencil buffer
     glGenRenderbuffersEXT(1, &fbo_depth_stencil);
     glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, fbo_depth_stencil);
-    glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH24_STENCIL8_EXT, width, height);
+    glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH24_STENCIL8_EXT, w, h);
     glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, 0);
 
     glGenRenderbuffersEXT(1, &fbo_color);
     glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, fbo_color);
-    glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_RGBA8, width, height);
+    glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_RGBA8, w, h);
     glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, 0);
 
     glGenFramebuffersEXT(1, &fbo);
@@ -94,29 +74,46 @@ void HeadlessView::resize(uint16_t width, uint16_t height, float pixelRatio) {
     GLenum status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT);
 
     if (status != GL_FRAMEBUFFER_COMPLETE_EXT) {
-        fprintf(stderr, "Couldn't create framebuffer: ");
+        std::stringstream error("Couldn't create framebuffer: ");
         switch (status) {
-            case GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT_EXT: fprintf(stderr, "incomplete attachment\n"); break;
-            case GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT_EXT: fprintf(stderr, "incomplete missing attachment\n"); break;
-            case GL_FRAMEBUFFER_INCOMPLETE_DRAW_BUFFER_EXT: fprintf(stderr, "incomplete draw buffer\n"); break;
-            case GL_FRAMEBUFFER_UNSUPPORTED: fprintf(stderr, "unsupported\n"); break;
-            default: fprintf(stderr, "other\n"); break;
+            case GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT_EXT: (error << "incomplete attachment\n"); break;
+            case GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT_EXT: error << "incomplete missing attachment\n"; break;
+            case GL_FRAMEBUFFER_INCOMPLETE_DIMENSIONS_EXT: error << "incomplete dimensions\n"; break;
+            case GL_FRAMEBUFFER_INCOMPLETE_FORMATS_EXT: error << "incomplete formats\n"; break;
+            case GL_FRAMEBUFFER_INCOMPLETE_DRAW_BUFFER_EXT: error << "incomplete draw buffer\n"; break;
+            case GL_FRAMEBUFFER_INCOMPLETE_READ_BUFFER_EXT: error << "incomplete read buffer\n"; break;
+            case GL_FRAMEBUFFER_UNSUPPORTED: error << "unsupported\n"; break;
+            default: error << "other\n"; break;
         }
-        return;
+        throw std::runtime_error(error.str());
     }
+
+    make_inactive();
 #endif
 
 #if MBGL_USE_GLX
-    x_pixmap = XCreatePixmap(x_display, DefaultRootWindow(x_display), width, height, 32);
+    x_pixmap = XCreatePixmap(x_display, DefaultRootWindow(x_display), w, h, 32);
     glx_pixmap = glXCreateGLXPixmap(x_display, x_info, x_pixmap);
+#endif
+}
+
+const std::unique_ptr<uint32_t[]> HeadlessView::readPixels() {
+    const unsigned int w = width_ * pixelRatio_;
+    const unsigned int h = height_ * pixelRatio_;
+
+    std::unique_ptr<uint32_t[]> pixels(new uint32_t[w * h]);
 
     make_active();
-#endif
+    glReadPixels(0, 0, width_, height_, GL_RGBA, GL_UNSIGNED_BYTE, pixels.get());
+    make_inactive();
 
+    return pixels;
 }
 
 void HeadlessView::clear_buffers() {
 #if MBGL_USE_CGL
+    make_active();
+
     glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
 
     if (fbo) {
@@ -133,6 +130,8 @@ void HeadlessView::clear_buffers() {
         glDeleteRenderbuffersEXT(1, &fbo_depth_stencil);
         fbo_depth_stencil = 0;
     }
+
+    make_inactive();
 #endif
 
 #if MBGL_USE_GLX
@@ -145,6 +144,8 @@ void HeadlessView::clear_buffers() {
         XFreePixmap(x_display, x_pixmap);
         x_pixmap = 0;
     }
+
+    make_inactive();
 #endif
 }
 
@@ -156,10 +157,7 @@ HeadlessView::~HeadlessView() {
 #endif
 
 #if MBGL_USE_GLX
-    glXMakeCurrent(x_display, None, NULL);
     glXDestroyContext(x_display, gl_context);
-    XFree(x_info);
-    XCloseDisplay(x_display);
 #endif
 }
 
@@ -175,13 +173,28 @@ void HeadlessView::make_active() {
 #if MBGL_USE_CGL
     CGLError error = CGLSetCurrentContext(gl_context);
     if (error) {
-        fprintf(stderr, "Switching OpenGL context failed\n");
+        throw std::runtime_error("Switching OpenGL context failed\n");
     }
 #endif
 
 #if MBGL_USE_GLX
     if (!glXMakeCurrent(x_display, glx_pixmap, gl_context)) {
-        fprintf(stderr, "Switching OpenGL context failed\n");
+        throw std::runtime_error("Switching OpenGL context failed\n");
+    }
+#endif
+}
+
+void HeadlessView::make_inactive() {
+#if MBGL_USE_CGL
+    CGLError error = CGLSetCurrentContext(nullptr);
+    if (error) {
+        throw std::runtime_error("Removing OpenGL context failed\n");
+    }
+#endif
+
+#if MBGL_USE_GLX
+    if (!glXMakeCurrent(x_display, 0, NULL)) {
+        throw std::runtime_error("Removing OpenGL context failed\n");
     }
 #endif
 }
diff --git a/common/headless_view.hpp b/common/headless_view.hpp
index 42f9c46da2..d2fe75382a 100644
--- a/common/headless_view.hpp
+++ b/common/headless_view.hpp
@@ -1,37 +1,49 @@
-#ifndef MBGL_COMMON_HEADLESS_CGL
-#define MBGL_COMMON_HEADLESS_CGL
+#ifndef MBGL_COMMON_HEADLESS_VIEW
+#define MBGL_COMMON_HEADLESS_VIEW
 
 #ifdef __APPLE__
 #define MBGL_USE_CGL 1
 #else
-#include <GL/glx.h>
+#include "glx.h"
 #define MBGL_USE_GLX 1
 #endif
 
 #include <mbgl/map/view.hpp>
 #include <mbgl/platform/gl.hpp>
-#include <mbgl/util/time.hpp>
+
+#include <memory>
 
 namespace mbgl {
 
+class HeadlessDisplay;
+
 class HeadlessView : public View {
 public:
     HeadlessView();
+    HeadlessView(std::shared_ptr<HeadlessDisplay> display);
     ~HeadlessView();
 
+    void createContext();
+
     void resize(uint16_t width, uint16_t height, float pixelRatio);
+    const std::unique_ptr<uint32_t[]> readPixels();
 
     void notify();
     void notify_map_change(MapChange change, timestamp delay = 0);
     void make_active();
+    void make_inactive();
     void swap();
     unsigned int root_fbo();
 
 private:
     void clear_buffers();
 
-
 private:
+    std::shared_ptr<HeadlessDisplay> display_;
+    uint16_t width_;
+    uint16_t height_;
+    float pixelRatio_;
+
 #if MBGL_USE_CGL
     CGLContextObj gl_context;
     GLuint fbo = 0;
@@ -40,9 +52,9 @@ private:
 #endif
 
 #if MBGL_USE_GLX
-    GLXContext gl_context = nullptr;
-    XVisualInfo *x_info = nullptr;
     Display *x_display = nullptr;
+    XVisualInfo *x_info = nullptr;
+    GLXContext gl_context = nullptr;
     Pixmap x_pixmap = 0;
     GLXPixmap glx_pixmap = 0;
 #endif