Add sw support to viewer on Linux.

tools/viewer/Viewer.cpp

Index: tools/viewer/Viewer.cpp
diff --git a/tools/viewer/Viewer.cpp b/tools/viewer/Viewer.cpp
index e5432b0ffa4c05f2b67f9689097642d7613e61b1..eb8097282891c4237c5fd92e1bd22f2a4b30e6fe 100644
--- a/tools/viewer/Viewer.cpp
+++ b/tools/viewer/Viewer.cpp
@@ -58,16 +58,23 @@ DEFINE_string2(match, m, nullptr,
                "^ and $ requires an exact match\n"
                "If a bench does not match any list entry,\n"
                "it is skipped unless some list entry starts with ~");
+
+#ifdef SK_VULKAN
+#    define BACKENDS_STR "\"sw\", \"gl\", and \"vulkan\""
+#else
+#    define BACKENDS_STR "\"sw\" and \"gl\""
+#endif
+
 #ifdef SK_BUILD_FOR_ANDROID
 DEFINE_string(skps, "/data/local/tmp/skia", "Directory to read skps from.");
 DEFINE_string(jpgs, "/data/local/tmp/skia", "Directory to read jpgs from.");
-DEFINE_bool(vulkan, false, "Run with Vulkan.");
 #else
 DEFINE_string(skps, "skps", "Directory to read skps from.");
 DEFINE_string(jpgs, "jpgs", "Directory to read jpgs from.");
-DEFINE_bool(vulkan, true, "Run with Vulkan.");
 #endif
 
+DEFINE_string2(backend, b, "sw", "Backend to use. Allowed values are " BACKENDS_STR ".");
+
 const char *kBackendTypeStrings[sk_app::Window::kBackendTypeCount] = {
     " [OpenGL]",
 #ifdef SK_VULKAN
@@ -76,6 +83,22 @@ const char *kBackendTypeStrings[sk_app::Window::kBackendTypeCount] = {
     " [Raster]"
 };
 
+static sk_app::Window::BackendType get_backend_type(const char* str) {
+#ifdef SK_VULKAN
+    if (0 == strcmp(str, "vk")) {
+        return sk_app::Window::kVulkan_BackendType;
+    } else
+#endif
+    if (0 == strcmp(str, "gl")) {
+        return sk_app::Window::kNativeGL_BackendType;
+    } else if (0 == strcmp(str, "sw")) {
+        return sk_app::Window::kRaster_BackendType;
+    } else {
+        SkDebugf("Unknown backend type, %s, defaulting to sw.", str);
+        return sk_app::Window::kRaster_BackendType;
+    }
+}
+
 const char* kName = "name";
 const char* kValue = "value";
 const char* kOptions = "options";
@@ -110,10 +133,7 @@ Viewer::Viewer(int argc, char** argv, void* platformData)
 
     SkCommandLineFlags::Parse(argc, argv);
 
-#ifdef SK_VULKAN
-    fBackendType = FLAGS_vulkan ? sk_app::Window::kVulkan_BackendType
-                                : sk_app::Window::kNativeGL_BackendType;
-#endif
+    fBackendType = get_backend_type(FLAGS_backend[0]);
     fWindow = Window::CreateNativeWindow(platformData);
     fWindow->attach(fBackendType, DisplayParams());