Add style change functionality to the Linux test app

Makes the life of people using Linux as development environment way
easier.

Just press 's' to cycle through 3 different styles.

include/mbgl/platform/default/glfw_view.hpp

@@ -25,10 +25,16 @@ public:
     static void onMouseClick(GLFWwindow *window, int button, int action, int modifiers);
     static void onMouseMove(GLFWwindow *window, double x, double y);
 
+    // Callback called when the user presses the key mapped to style change.
+    // The expected action is to set a new style, different to the current one.
+    void setChangeStyleCallback(std::function<void()> callback);
+
     void run();
     void fps();
 
-public:
+    GLFWwindow *window = nullptr;
+
+private:
     bool fullscreen = false;
 
     double lastX = 0, lastY = 0;
@@ -38,7 +44,7 @@ public:
 
     double lastClick = -1;
 
-    GLFWwindow *window = nullptr;
+    std::function<void()> changeStyleCallback;
 };
 
 #endif

include/mbgl/util/constants.hpp

@@ -3,6 +3,7 @@
 
 #include <cmath>
 #include <string>
+#include <vector>
 
 namespace mbgl {
 

linux/main.cpp

@@ -1,4 +1,5 @@
 #include <mbgl/mbgl.hpp>
+#include "../platform/default/default_styles.hpp"
 #include <mbgl/util/std.hpp>
 #include <mbgl/util/uv.hpp>
 #include <mbgl/platform/log.hpp>
@@ -13,9 +14,12 @@
 #include <fstream>
 #include <sstream>
 
+namespace {
 
 std::unique_ptr<GLFWView> view;
 
+}
+
 void quit_handler(int) {
     if (view) {
         mbgl::Log::Info(mbgl::Event::Setup, "waiting for quit...");
@@ -75,6 +79,19 @@ int main(int argc, char *argv[]) {
     map.setBearing(settings.bearing);
     map.setDebug(settings.debug);
 
+    view->setChangeStyleCallback([&map] () {
+        static uint8_t currentStyleIndex;
+
+        if (++currentStyleIndex == mbgl::util::defaultStyles.size()) {
+            currentStyleIndex = 0;
+        }
+
+        const auto& newStyle = mbgl::util::defaultStyles[currentStyleIndex];
+        map.setStyleURL(newStyle.first);
+
+        mbgl::Log::Info(mbgl::Event::Setup, std::string("Changed style to: ") + newStyle.first);
+    });
+
     // Set access token if present
     const char *token = getenv("MAPBOX_ACCESS_TOKEN");
     if (token == nullptr) {
@@ -85,7 +102,7 @@ int main(int argc, char *argv[]) {
 
     // Load style
     if (style.empty()) {
-        style = std::string("asset://") + std::string("styles/bright-v7.json");
+        style = mbgl::util::defaultStyles.front().first;
     }
 
     map.setStyleURL(style);

linux/mapboxgl-app.gypi

@@ -20,8 +20,11 @@
       'sources': [
         'main.cpp',
         '../platform/default/settings_json.cpp',
+        '../platform/default/glfw_view.hpp',
         '../platform/default/glfw_view.cpp',
         '../platform/default/log_stderr.cpp',
+        '../platform/default/default_styles.hpp',
+        '../platform/default/default_styles.cpp',
       ],
 
       'variables' : {

platform/default/default_styles.cpp

@@ -0,0 +1,18 @@
+#include "default_styles.hpp"
+
+namespace mbgl {
+namespace util {
+
+const std::vector<std::pair<std::string, std::string>> defaultStyles = {
+    { "asset://styles/mapbox-streets-v7.json", "Mapbox Streets" },
+    { "asset://styles/emerald-v7.json", "Emerald" },
+    { "asset://styles/light-v7.json", "Light" },
+    { "asset://styles/dark-v7.json", "Dark" },
+    { "asset://styles/bright-v7.json", "Bright" },
+    { "asset://styles/basic-v7.json", "Basic" },
+    { "asset://styles/outdoors-v7.json", "Outdoors" },
+    { "asset://styles/satellite-v7.json", "Satellite" },
+};
+
+} // end namespace util
+} // end namespace mbgl

platform/default/default_styles.hpp

@@ -0,0 +1,17 @@
+#ifndef MBGL_PLATFORM_DEFAULT_STYLES
+#define MBGL_PLATFORM_DEFAULT_STYLES
+
+#include <vector>
+#include <string>
+
+namespace mbgl {
+namespace util {
+
+// A list of default styles, with the first string being the URL
+// and the second being the user-visible name.
+extern const std::vector<std::pair<std::string, std::string>> defaultStyles;
+
+} // end namespace util
+} // end namespace mbgl
+
+#endif

platform/default/glfw_view.cpp

@@ -179,6 +179,10 @@ void GLFWView::onKey(GLFWwindow *window, int key, int /*scancode*/, int action,
             if (!mods)
                 view->map->resetPosition();
             break;
+        case GLFW_KEY_S:
+            if (view->changeStyleCallback)
+                view->changeStyleCallback();
+            break;
         case GLFW_KEY_R:
             if (!mods) {
                 view->map->setDefaultTransitionDuration(std::chrono::milliseconds(300));
@@ -306,6 +310,10 @@ void GLFWView::fps() {
     }
 }
 
+void GLFWView::setChangeStyleCallback(std::function<void()> callback) {
+    changeStyleCallback = callback;
+}
+
 namespace mbgl {
 namespace platform {