1 files changed, 630 insertions, 0 deletions

diff --git a/platform/glfw/glfw_view.cpp b/platform/glfw/glfw_view.cpp
new file mode 100644
index 0000000000..fdf82fda8f
--- /dev/null
+++ b/platform/glfw/glfw_view.cpp
@@ -0,0 +1,630 @@
+#include "glfw_view.hpp"
+
+#include <mbgl/annotation/annotation.hpp>
+#include <mbgl/sprite/sprite_image.hpp>
+#include <mbgl/style/transition_options.hpp>
+#include <mbgl/gl/gl.hpp>
+#include <mbgl/gl/extension.hpp>
+#include <mbgl/gl/context.hpp>
+#include <mbgl/util/logging.hpp>
+#include <mbgl/util/platform.hpp>
+#include <mbgl/util/string.hpp>
+#include <mbgl/util/chrono.hpp>
+#include <mbgl/map/camera.hpp>
+
+#include <mbgl/gl/state.hpp>
+#include <mbgl/gl/value.hpp>
+
+#include <cassert>
+#include <cstdlib>
+
+void glfwError(int error, const char *description) {
+    mbgl::Log::Error(mbgl::Event::OpenGL, "GLFW error (%i): %s", error, description);
+    assert(false);
+}
+
+GLFWView::GLFWView(bool fullscreen_, bool benchmark_)
+    : fullscreen(fullscreen_), benchmark(benchmark_) {
+    glfwSetErrorCallback(glfwError);
+
+    std::srand(std::time(nullptr));
+
+    if (!glfwInit()) {
+        mbgl::Log::Error(mbgl::Event::OpenGL, "failed to initialize glfw");
+        exit(1);
+    }
+
+    GLFWmonitor *monitor = nullptr;
+    if (fullscreen) {
+        monitor = glfwGetPrimaryMonitor();
+        auto videoMode = glfwGetVideoMode(monitor);
+        width = videoMode->width;
+        height = videoMode->height;
+    }
+
+#ifdef DEBUG
+    glfwWindowHint(GLFW_OPENGL_DEBUG_CONTEXT, GL_TRUE);
+#endif
+
+#ifdef GL_ES_VERSION_2_0
+    glfwWindowHint(GLFW_CLIENT_API, GLFW_OPENGL_ES_API);
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 2);
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);
+#endif
+
+    glfwWindowHint(GLFW_RED_BITS, 8);
+    glfwWindowHint(GLFW_GREEN_BITS, 8);
+    glfwWindowHint(GLFW_BLUE_BITS, 8);
+    glfwWindowHint(GLFW_ALPHA_BITS, 8);
+    glfwWindowHint(GLFW_STENCIL_BITS, 8);
+    glfwWindowHint(GLFW_DEPTH_BITS, 16);
+
+    window = glfwCreateWindow(width, height, "Mapbox GL", monitor, nullptr);
+    if (!window) {
+        glfwTerminate();
+        mbgl::Log::Error(mbgl::Event::OpenGL, "failed to initialize window");
+        exit(1);
+    }
+
+    glfwSetWindowUserPointer(window, this);
+    glfwMakeContextCurrent(window);
+    if (benchmark) {
+        // Disables vsync on platforms that support it.
+        glfwSwapInterval(0);
+    } else {
+        glfwSwapInterval(1);
+    }
+
+
+    glfwSetCursorPosCallback(window, onMouseMove);
+    glfwSetMouseButtonCallback(window, onMouseClick);
+    glfwSetWindowSizeCallback(window, onWindowResize);
+    glfwSetFramebufferSizeCallback(window, onFramebufferResize);
+    glfwSetScrollCallback(window, onScroll);
+    glfwSetKeyCallback(window, onKey);
+
+    mbgl::gl::InitializeExtensions(glfwGetProcAddress);
+
+    glfwGetWindowSize(window, &width, &height);
+    glfwGetFramebufferSize(window, &fbWidth, &fbHeight);
+    pixelRatio = static_cast<float>(fbWidth) / width;
+
+    glfwMakeContextCurrent(nullptr);
+
+    printf("\n");
+    printf("================================================================================\n");
+    printf("\n");
+    printf("- Press `S` to cycle through bundled styles\n");
+    printf("- Press `X` to reset the transform\n");
+    printf("- Press `N` to reset north\n");
+    printf("- Press `R` to toggle any available `night` style class\n");
+    printf("- Press `Z` to cycle through north orientations\n");
+    printf("- Prezz `X` to cycle through the viewport modes\n");
+    printf("- Press `A` to cycle through Mapbox offices in the world + dateline monument\n");
+    printf("- Press `B` to cycle through the color, stencil, and depth buffer\n");
+    printf("\n");
+    printf("- Press `1` through `6` to add increasing numbers of point annotations for testing\n");
+    printf("- Press `7` through `0` to add increasing numbers of shape annotations for testing\n");
+    printf("\n");
+    printf("- Press `Q` to remove annotations\n");
+    printf("- Press `P` to add a random custom runtime imagery annotation\n");
+    printf("- Press `L` to add a random line annotation\n");
+    printf("- Press `W` to pop the last-added annotation off\n");
+    printf("\n");
+    printf("- `Control` + mouse drag to rotate\n");
+    printf("- `Shift` + mouse drag to tilt\n");
+    printf("\n");
+    printf("- Press `Tab` to cycle through the map debug options\n");
+    printf("- Press `Esc` to quit\n");
+    printf("\n");
+    printf("================================================================================\n");
+    printf("\n");
+}
+
+GLFWView::~GLFWView() {
+    glfwDestroyWindow(window);
+    glfwTerminate();
+}
+
+void GLFWView::setMap(mbgl::Map *map_) {
+    map = map_;
+    map->addAnnotationIcon("default_marker", makeSpriteImage(22, 22, 1));
+}
+
+void GLFWView::updateViewBinding() {
+    getContext().bindFramebuffer.setCurrentValue(0);
+    assert(mbgl::gl::value::BindFramebuffer::Get() == getContext().bindFramebuffer.getCurrentValue());
+    getContext().viewport.setCurrentValue({ 0, 0, getFramebufferSize() });
+    assert(mbgl::gl::value::Viewport::Get() == getContext().viewport.getCurrentValue());
+}
+
+void GLFWView::bind() {
+    getContext().bindFramebuffer = 0;
+    getContext().viewport = { 0, 0, getFramebufferSize() };
+}
+
+void GLFWView::onKey(GLFWwindow *window, int key, int /*scancode*/, int action, int mods) {
+    GLFWView *view = reinterpret_cast<GLFWView *>(glfwGetWindowUserPointer(window));
+
+    if (action == GLFW_RELEASE) {
+        switch (key) {
+        case GLFW_KEY_ESCAPE:
+            glfwSetWindowShouldClose(window, true);
+            break;
+        case GLFW_KEY_TAB:
+            view->map->cycleDebugOptions();
+            break;
+        case GLFW_KEY_X:
+            if (!mods)
+                view->map->resetPosition();
+            break;
+        case GLFW_KEY_S:
+            if (view->changeStyleCallback)
+                view->changeStyleCallback();
+            break;
+        case GLFW_KEY_R:
+            if (!mods) {
+                static const mbgl::style::TransitionOptions transition { { mbgl::Milliseconds(300) } };
+                view->map->setTransitionOptions(transition);
+                if (view->map->hasClass("night")) {
+                    view->map->removeClass("night");
+                } else {
+                    view->map->addClass("night");
+                }
+            }
+            break;
+#if not MBGL_USE_GLES2
+        case GLFW_KEY_B: {
+            auto debug = view->map->getDebug();
+            if (debug & mbgl::MapDebugOptions::StencilClip) {
+                debug &= ~mbgl::MapDebugOptions::StencilClip;
+                debug |= mbgl::MapDebugOptions::DepthBuffer;
+            } else if (debug & mbgl::MapDebugOptions::DepthBuffer) {
+                debug &= ~mbgl::MapDebugOptions::DepthBuffer;
+            } else {
+                debug |= mbgl::MapDebugOptions::StencilClip;
+            }
+            view->map->setDebug(debug);
+        } break;
+#endif // MBGL_USE_GLES2
+        case GLFW_KEY_N:
+            if (!mods)
+                view->map->resetNorth();
+            break;
+        case GLFW_KEY_Z:
+            view->nextOrientation();
+            break;
+        case GLFW_KEY_Q: {
+            auto result = view->map->queryPointAnnotations({ {}, { double(view->getSize().width), double(view->getSize().height) } });
+            printf("visible point annotations: %lu\n", result.size());
+        } break;
+        case GLFW_KEY_C:
+            view->clearAnnotations();
+            break;
+        case GLFW_KEY_P:
+            view->addRandomCustomPointAnnotations(1);
+            break;
+        case GLFW_KEY_L:
+            view->addRandomLineAnnotations(1);
+            break;
+        case GLFW_KEY_A: {
+            // XXX Fix precision loss in flyTo:
+            // https://github.com/mapbox/mapbox-gl-native/issues/4298
+            static const std::vector<mbgl::LatLng> places = {
+                mbgl::LatLng { -16.796665, -179.999983 },   // Dateline monument
+                mbgl::LatLng { 12.9810542, 77.6345551 },    // Mapbox Bengaluru, India
+                mbgl::LatLng { -13.15607,-74.21773 },       // Mapbox Peru
+                mbgl::LatLng { 37.77572, -122.4158818 },    // Mapbox SF, USA
+                mbgl::LatLng { 38.91318,-77.03255 },        // Mapbox DC, USA
+            };
+            static size_t nextPlace = 0;
+            mbgl::CameraOptions cameraOptions;
+            cameraOptions.center = places[nextPlace++];
+            cameraOptions.zoom = 20;
+            cameraOptions.pitch = 30;
+
+            mbgl::AnimationOptions animationOptions(mbgl::Seconds(10));
+            view->map->flyTo(cameraOptions, animationOptions);
+            nextPlace = nextPlace % places.size();
+        } break;
+        }
+    }
+
+    if (action == GLFW_RELEASE || action == GLFW_REPEAT) {
+        switch (key) {
+        case GLFW_KEY_W: view->popAnnotation(); break;
+        case GLFW_KEY_1: view->addRandomPointAnnotations(1); break;
+        case GLFW_KEY_2: view->addRandomPointAnnotations(10); break;
+        case GLFW_KEY_3: view->addRandomPointAnnotations(100); break;
+        case GLFW_KEY_4: view->addRandomPointAnnotations(1000); break;
+        case GLFW_KEY_5: view->addRandomPointAnnotations(10000); break;
+        case GLFW_KEY_6: view->addRandomPointAnnotations(100000); break;
+        case GLFW_KEY_7: view->addRandomShapeAnnotations(1); break;
+        case GLFW_KEY_8: view->addRandomShapeAnnotations(10); break;
+        case GLFW_KEY_9: view->addRandomShapeAnnotations(100); break;
+        case GLFW_KEY_0: view->addRandomShapeAnnotations(1000); break;
+        }
+    }
+}
+
+mbgl::Color GLFWView::makeRandomColor() const {
+    const float r = 1.0f * (float(std::rand()) / RAND_MAX);
+    const float g = 1.0f * (float(std::rand()) / RAND_MAX);
+    const float b = 1.0f * (float(std::rand()) / RAND_MAX);
+    return { r, g, b, 1.0f };
+}
+
+mbgl::Point<double> GLFWView::makeRandomPoint() const {
+    const double x = width * double(std::rand()) / RAND_MAX;
+    const double y = height * double(std::rand()) / RAND_MAX;
+    mbgl::LatLng latLng = map->latLngForPixel({ x, y });
+    return { latLng.longitude, latLng.latitude };
+}
+
+std::shared_ptr<const mbgl::SpriteImage>
+GLFWView::makeSpriteImage(int width, int height, float pixelRatio) {
+    const int r = 255 * (double(std::rand()) / RAND_MAX);
+    const int g = 255 * (double(std::rand()) / RAND_MAX);
+    const int b = 255 * (double(std::rand()) / RAND_MAX);
+
+    const int w = std::ceil(pixelRatio * width);
+    const int h = std::ceil(pixelRatio * height);
+
+    mbgl::PremultipliedImage image({ static_cast<uint32_t>(w), static_cast<uint32_t>(h) });
+    auto data = reinterpret_cast<uint32_t*>(image.data.get());
+    const int dist = (w / 2) * (w / 2);
+    for (int y = 0; y < h; y++) {
+        for (int x = 0; x < w; x++) {
+            const int dx = x - w / 2;
+            const int dy = y - h / 2;
+            const int diff = dist - (dx * dx + dy * dy);
+            if (diff > 0) {
+                const int a = std::min(0xFF, diff) * 0xFF / dist;
+                // Premultiply the rgb values with alpha
+                data[w * y + x] =
+                    (a << 24) | ((a * r / 0xFF) << 16) | ((a * g / 0xFF) << 8) | (a * b / 0xFF);
+            }
+        }
+    }
+
+    return std::make_shared<mbgl::SpriteImage>(std::move(image), pixelRatio);
+}
+
+void GLFWView::nextOrientation() {
+    using NO = mbgl::NorthOrientation;
+    switch (map->getNorthOrientation()) {
+        case NO::Upwards: map->setNorthOrientation(NO::Rightwards); break;
+        case NO::Rightwards: map->setNorthOrientation(NO::Downwards); break;
+        case NO::Downwards: map->setNorthOrientation(NO::Leftwards); break;
+        default: map->setNorthOrientation(NO::Upwards); break;
+    }
+}
+
+void GLFWView::addRandomCustomPointAnnotations(int count) {
+    for (int i = 0; i < count; i++) {
+        static int spriteID = 1;
+        const auto name = std::string{ "marker-" } + mbgl::util::toString(spriteID++);
+        map->addAnnotationIcon(name, makeSpriteImage(22, 22, 1));
+        spriteIDs.push_back(name);
+        annotationIDs.push_back(map->addAnnotation(mbgl::SymbolAnnotation { makeRandomPoint(), name }));
+    }
+}
+
+void GLFWView::addRandomPointAnnotations(int count) {
+    for (int i = 0; i < count; ++i) {
+        annotationIDs.push_back(map->addAnnotation(mbgl::SymbolAnnotation { makeRandomPoint(), "default_marker" }));
+    }
+}
+
+void GLFWView::addRandomLineAnnotations(int count) {
+    for (int i = 0; i < count; ++i) {
+        mbgl::LineString<double> lineString;
+        for (int j = 0; j < 3; ++j) {
+            lineString.push_back(makeRandomPoint());
+        }
+        annotationIDs.push_back(map->addAnnotation(mbgl::LineAnnotation { lineString, 1.0f, 2.0f, { makeRandomColor() } }));
+    }
+}
+
+void GLFWView::addRandomShapeAnnotations(int count) {
+    for (int i = 0; i < count; ++i) {
+        mbgl::Polygon<double> triangle;
+        triangle.push_back({ makeRandomPoint(), makeRandomPoint(), makeRandomPoint() });
+        annotationIDs.push_back(map->addAnnotation(mbgl::FillAnnotation { triangle, 0.5f, { makeRandomColor() }, { makeRandomColor() } }));
+    }
+}
+
+void GLFWView::clearAnnotations() {
+    for (const auto& id : annotationIDs) {
+        map->removeAnnotation(id);
+    }
+
+    annotationIDs.clear();
+}
+
+void GLFWView::popAnnotation() {
+    if (annotationIDs.empty()) {
+        return;
+    }
+
+    map->removeAnnotation(annotationIDs.back());
+    annotationIDs.pop_back();
+}
+
+void GLFWView::onScroll(GLFWwindow *window, double /*xOffset*/, double yOffset) {
+    GLFWView *view = reinterpret_cast<GLFWView *>(glfwGetWindowUserPointer(window));
+    double delta = yOffset * 40;
+
+    bool isWheel = delta != 0 && std::fmod(delta, 4.000244140625) == 0;
+
+    double absDelta = delta < 0 ? -delta : delta;
+    double scale = 2.0 / (1.0 + std::exp(-absDelta / 100.0));
+
+    // Make the scroll wheel a bit slower.
+    if (!isWheel) {
+        scale = (scale - 1.0) / 2.0 + 1.0;
+    }
+
+    // Zooming out.
+    if (delta < 0 && scale != 0) {
+        scale = 1.0 / scale;
+    }
+
+    view->map->scaleBy(scale, mbgl::ScreenCoordinate { view->lastX, view->lastY });
+}
+
+void GLFWView::onWindowResize(GLFWwindow *window, int width, int height) {
+    GLFWView *view = reinterpret_cast<GLFWView *>(glfwGetWindowUserPointer(window));
+    view->width = width;
+    view->height = height;
+    view->map->setSize({ static_cast<uint32_t>(view->width), static_cast<uint32_t>(view->height) });
+}
+
+void GLFWView::onFramebufferResize(GLFWwindow *window, int width, int height) {
+    GLFWView *view = reinterpret_cast<GLFWView *>(glfwGetWindowUserPointer(window));
+    view->fbWidth = width;
+    view->fbHeight = height;
+
+    // This is only triggered when the framebuffer is resized, but not the window. It can
+    // happen when you move the window between screens with a different pixel ratio.
+    // We are forcing a repaint my invalidating the view, which triggers a rerender with the
+    // new framebuffer dimensions.
+    view->invalidate();
+}
+
+void GLFWView::onMouseClick(GLFWwindow *window, int button, int action, int modifiers) {
+    GLFWView *view = reinterpret_cast<GLFWView *>(glfwGetWindowUserPointer(window));
+
+    if (button == GLFW_MOUSE_BUTTON_RIGHT ||
+        (button == GLFW_MOUSE_BUTTON_LEFT && modifiers & GLFW_MOD_CONTROL)) {
+        view->rotating = action == GLFW_PRESS;
+        view->map->setGestureInProgress(view->rotating);
+    } else if (button == GLFW_MOUSE_BUTTON_LEFT && (modifiers & GLFW_MOD_SHIFT)) {
+        view->pitching = action == GLFW_PRESS;
+        view->map->setGestureInProgress(view->pitching);
+    } else if (button == GLFW_MOUSE_BUTTON_LEFT) {
+        view->tracking = action == GLFW_PRESS;
+        view->map->setGestureInProgress(view->tracking);
+
+        if (action == GLFW_RELEASE) {
+            double now = glfwGetTime();
+            if (now - view->lastClick < 0.4 /* ms */) {
+                if (modifiers & GLFW_MOD_SHIFT) {
+                    view->map->scaleBy(0.5, mbgl::ScreenCoordinate { view->lastX, view->lastY }, mbgl::Milliseconds(500));
+                } else {
+                    view->map->scaleBy(2.0, mbgl::ScreenCoordinate { view->lastX, view->lastY }, mbgl::Milliseconds(500));
+                }
+            }
+            view->lastClick = now;
+        }
+    }
+}
+
+void GLFWView::onMouseMove(GLFWwindow *window, double x, double y) {
+    GLFWView *view = reinterpret_cast<GLFWView *>(glfwGetWindowUserPointer(window));
+    if (view->tracking) {
+        double dx = x - view->lastX;
+        double dy = y - view->lastY;
+        if (dx || dy) {
+            view->map->setLatLng(
+                    view->map->latLngForPixel(mbgl::ScreenCoordinate(x - dx, y - dy)),
+                    mbgl::ScreenCoordinate(x, y));
+        }
+    } else if (view->rotating) {
+        view->map->rotateBy({ view->lastX, view->lastY }, { x, y });
+    } else if (view->pitching) {
+        const double dy = y - view->lastY;
+        if (dy) {
+            view->map->setPitch(view->map->getPitch() - dy / 2);
+        }
+    }
+    view->lastX = x;
+    view->lastY = y;
+}
+
+void GLFWView::run() {
+    auto callback = [&] {
+        if (glfwWindowShouldClose(window)) {
+            runLoop.stop();
+            return;
+        }
+
+        glfwPollEvents();
+
+        if (dirty) {
+            const double started = glfwGetTime();
+
+            glfwMakeContextCurrent(window);
+
+            updateViewBinding();
+            map->render(*this);
+
+            glfwSwapBuffers(window);
+
+            report(1000 * (glfwGetTime() - started));
+            if (benchmark) {
+                invalidate();
+            }
+
+            dirty = false;
+        }
+    };
+
+    frameTick.start(mbgl::Duration::zero(), mbgl::Milliseconds(1000 / 60), callback);
+#if defined(__APPLE__)
+    while (!glfwWindowShouldClose(window)) runLoop.run();
+#else
+    runLoop.run();
+#endif
+}
+
+float GLFWView::getPixelRatio() const {
+    return pixelRatio;
+}
+
+mbgl::Size GLFWView::getSize() const {
+    return { static_cast<uint32_t>(width), static_cast<uint32_t>(height) };
+}
+
+mbgl::Size GLFWView::getFramebufferSize() const {
+    return { static_cast<uint32_t>(fbWidth), static_cast<uint32_t>(fbHeight) };
+}
+
+void GLFWView::activate() {
+    glfwMakeContextCurrent(window);
+}
+
+void GLFWView::deactivate() {
+    glfwMakeContextCurrent(nullptr);
+}
+
+void GLFWView::invalidate() {
+    dirty = true;
+    glfwPostEmptyEvent();
+}
+
+void GLFWView::report(float duration) {
+    frames++;
+    frameTime += duration;
+
+    const double currentTime = glfwGetTime();
+    if (currentTime - lastReported >= 1) {
+        frameTime /= frames;
+        mbgl::Log::Info(mbgl::Event::OpenGL, "Frame time: %6.2fms (%6.2f fps)", frameTime,
+            1000 / frameTime);
+        frames = 0;
+        frameTime = 0;
+        lastReported = currentTime;
+    }
+}
+
+void GLFWView::setChangeStyleCallback(std::function<void()> callback) {
+    changeStyleCallback = callback;
+}
+
+void GLFWView::setShouldClose() {
+    glfwSetWindowShouldClose(window, true);
+    glfwPostEmptyEvent();
+}
+
+void GLFWView::setWindowTitle(const std::string& title) {
+    glfwSetWindowTitle(window, (std::string { "Mapbox GL: " } + title).c_str());
+}
+
+void GLFWView::setMapChangeCallback(std::function<void(mbgl::MapChange)> callback) {
+    this->mapChangeCallback = callback;
+}
+
+void GLFWView::notifyMapChange(mbgl::MapChange change) {
+    if (mapChangeCallback) {
+        mapChangeCallback(change);
+    }
+}
+
+namespace mbgl {
+namespace platform {
+
+#ifndef GL_ES_VERSION_2_0
+void showDebugImage(std::string name, const char *data, size_t width, size_t height) {
+    glfwInit();
+
+    static GLFWwindow *debugWindow = nullptr;
+    if (!debugWindow) {
+        debugWindow = glfwCreateWindow(width, height, name.c_str(), nullptr, nullptr);
+        if (!debugWindow) {
+            glfwTerminate();
+            fprintf(stderr, "Failed to initialize window\n");
+            exit(1);
+        }
+    }
+
+    GLFWwindow *currentWindow = glfwGetCurrentContext();
+
+    glfwSetWindowSize(debugWindow, width, height);
+    glfwMakeContextCurrent(debugWindow);
+
+    int fbWidth, fbHeight;
+    glfwGetFramebufferSize(debugWindow, &fbWidth, &fbHeight);
+    float scale = static_cast<float>(fbWidth) / static_cast<float>(width);
+
+    {
+        gl::PreserveState<gl::value::PixelZoom> pixelZoom;
+        gl::PreserveState<gl::value::RasterPos> rasterPos;
+
+        MBGL_CHECK_ERROR(glPixelZoom(scale, -scale));
+        MBGL_CHECK_ERROR(glRasterPos2f(-1.0f, 1.0f));
+        MBGL_CHECK_ERROR(glDrawPixels(width, height, GL_LUMINANCE, GL_UNSIGNED_BYTE, data));
+    }
+
+    glfwSwapBuffers(debugWindow);
+
+    glfwMakeContextCurrent(currentWindow);
+}
+
+void showColorDebugImage(std::string name, const char *data, size_t logicalWidth, size_t logicalHeight, size_t width, size_t height) {
+    glfwInit();
+
+    static GLFWwindow *debugWindow = nullptr;
+    if (!debugWindow) {
+        debugWindow = glfwCreateWindow(logicalWidth, logicalHeight, name.c_str(), nullptr, nullptr);
+        if (!debugWindow) {
+            glfwTerminate();
+            fprintf(stderr, "Failed to initialize window\n");
+            exit(1);
+        }
+    }
+
+    GLFWwindow *currentWindow = glfwGetCurrentContext();
+
+    glfwSetWindowSize(debugWindow, logicalWidth, logicalHeight);
+    glfwMakeContextCurrent(debugWindow);
+
+    int fbWidth, fbHeight;
+    glfwGetFramebufferSize(debugWindow, &fbWidth, &fbHeight);
+    float xScale = static_cast<float>(fbWidth) / static_cast<float>(width);
+    float yScale = static_cast<float>(fbHeight) / static_cast<float>(height);
+
+    {
+        gl::PreserveState<gl::value::ClearColor> clearColor;
+        gl::PreserveState<gl::value::Blend> blend;
+        gl::PreserveState<gl::value::BlendFunc> blendFunc;
+        gl::PreserveState<gl::value::PixelZoom> pixelZoom;
+        gl::PreserveState<gl::value::RasterPos> rasterPos;
+
+        MBGL_CHECK_ERROR(glClearColor(0.8, 0.8, 0.8, 1));
+        MBGL_CHECK_ERROR(glClear(GL_COLOR_BUFFER_BIT));
+        MBGL_CHECK_ERROR(glEnable(GL_BLEND));
+        MBGL_CHECK_ERROR(glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA));
+        MBGL_CHECK_ERROR(glPixelZoom(xScale, -yScale));
+        MBGL_CHECK_ERROR(glRasterPos2f(-1.0f, 1.0f));
+        MBGL_CHECK_ERROR(glDrawPixels(width, height, GL_RGBA, GL_UNSIGNED_INT_8_8_8_8_REV, data));
+    }
+
+    glfwSwapBuffers(debugWindow);
+
+    glfwMakeContextCurrent(currentWindow);
+}
+#endif
+
+} // namespace platform
+} // namespace mbgl