Mali Vulkan SDK for Android 1.0.0 Mali Developer Center
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Introduction to Vulkan on Android

Shows you how to create a Vulkan instance, device and swapchain on Android.

The Native Activity

To get a Vulkan surface up and running, we will use native code exclusively, using NativeActivity. NativeActivity is a built-in Java class in Android which lets us implement applications purely in native code. This is very useful for Vulkan since in order to create a Vulkan swapchain, we need an ANativeWindow handle, which NativeActivity will neatly give us.

We set up a sample with this AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.arm.vulkansdk.hellotriangle"
android:versionCode="1"
android:versionName="1.0">
<application android:label="@string/app_name" android:icon="@drawable/ic_launcher" android:hasCode="false">
<activity android:name="android.app.NativeActivity"
android:theme="@android:style/Theme.NoTitleBar.Fullscreen"
android:screenOrientation="landscape"
android:label="@string/app_name">
<meta-data android:name="android.app.lib_name" android:value="native" />
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>

The important part here is that we set android.app.NativeActivity as our launch activity, where we set the android.app.lib_name meta-data. This is so that the Android class can load our application. Using android:value="native", Android will load libnative.so. We also set the android:hasCode="false" field, since we will not need to build any Java code ourselves.

Inside libnative.so, we need to include some glue code which will translate Java callbacks over to a classic main loop.

// platform/android/android.cpp
#include "android_native_app_glue.h"
void android_main(android_app *state)
{
// Implement application here!
for (;;)
{
...
ALooper_pollAll(&event);
event->handle();
}
}

In this mainloop, we will poll the android looper to receive and handle events. One of the events we will handle is obtaining a window handle. This window handle is required for creating a Vulkan swapchain.

static void engineHandleCmd(android_app *pApp, int32_t cmd)
{
switch (cmd)
{
case APP_CMD_INIT_WINDOW:
ANativeWindow *pWindow = state->pApp->window;
// Pass pWindow on to the application somehow.
break;
}
}

Bringing up Vulkan Instance and Device

After we have obtained a native window, we can create a Vulkan instance. The Vulkan instance is our first entry point into Vulkan.

VkApplicationInfo app = { VK_STRUCTURE_TYPE_APPLICATION_INFO };
app.pApplicationName = "Mali SDK";
app.applicationVersion = 0;
app.pEngineName = "Mali SDK";
app.engineVersion = 0;
app.apiVersion = VK_API_VERSION;
VkInstanceCreateInfo instanceInfo = { VK_STRUCTURE_TYPE_INSTANCE_CREATE_INFO };
instanceInfo.pApplicationInfo = &app;
if (useInstanceExtensions)
{
instanceInfo.enabledExtensionCount = requiredInstanceExtensions.size();
instanceInfo.ppEnabledExtensionNames = requiredInstanceExtensions.data();
}
VkResult res = vkCreateInstance(&instanceInfo, nullptr, &instance);

The Vulkan instance represents the "loader". The Vulkan loader serves as a common entrypoint for Vulkan on a particular platform, and it is vendor-agnostic. From the instance, we can query the available GPUs on the system.

uint32_t gpuCount = 0;
VK_CHECK(vkEnumeratePhysicalDevices(instance, &gpuCount, nullptr));
if (gpuCount < 1)
{
LOGE("Failed to enumerate Vulkan physical device.\n");
return RESULT_ERROR_GENERIC;
}
vector<VkPhysicalDevice> gpus(gpuCount);
VK_CHECK(vkEnumeratePhysicalDevices(instance, &gpuCount, gpus.data()));

From here we can query the VkPhysicalDevice about particular features if we want to select one GPU among many. Once we have decided on a GPU to use, we can create a device from it. The Vulkan device will from this point on serve as our entry for dispatching work to the GPU.

static const float one = 1.0f;
VkDeviceQueueCreateInfo queueInfo = { VK_STRUCTURE_TYPE_DEVICE_QUEUE_CREATE_INFO };
queueInfo.queueFamilyIndex = graphicsQueueIndex;
queueInfo.queueCount = 1;
queueInfo.pQueuePriorities = &one;
VkPhysicalDeviceFeatures features = { false };
VkDeviceCreateInfo deviceInfo = { VK_STRUCTURE_TYPE_DEVICE_CREATE_INFO };
deviceInfo.queueCreateInfoCount = 1;
deviceInfo.pQueueCreateInfos = &queueInfo;
if (useDeviceExtensions)
{
deviceInfo.enabledExtensionCount = requiredDeviceExtensions.size();
deviceInfo.ppEnabledExtensionNames = requiredDeviceExtensions.data();
}
deviceInfo.pEnabledFeatures = &features;
VK_CHECK(vkCreateDevice(gpu, &deviceInfo, nullptr, &device));
if (FAILED(loadDeviceSymbols()))
return RESULT_ERROR_GENERIC;
vkGetDeviceQueue(device, graphicsQueueIndex, 0, &queue);

Creating a Vulkan Swapchain

Now that we have a device, we can create a swapchain. A swapchain is the way for Vulkan applications to render to the screen. Vulkan can be used completely without a screen for off-line processing, and rendering to screen is done via a common extension, VK_KHR_swapchain.

First, we need to create a Vulkan surface.

VkSurfaceKHR AndroidPlatform::createSurface()
{
VkSurfaceKHR surface;
auto fpCreateAndroidSurfaceKHR =
reinterpret_cast<PFN_vkCreateAndroidSurfaceKHR>(vkGetInstanceProcAddr(instance, "vkCreateAndroidSurfaceKHR"));
if (!fpCreateAndroidSurfaceKHR)
return VK_NULL_HANDLE;
VkAndroidSurfaceCreateInfoKHR info = { VK_STRUCTURE_TYPE_ANDROID_SURFACE_CREATE_INFO_KHR };
info.window = pNativeWindow;
VK_CHECK(fpCreateAndroidSurfaceKHR(instance, &info, nullptr, &surface));
return surface;
}
VkSwapchainCreateInfoKHR info = { VK_STRUCTURE_TYPE_SWAPCHAIN_CREATE_INFO_KHR };
info.surface = surface;
...
VK_CHECK(fpCreateSwapchainKHR(device, &info, nullptr, &swapchain));

After the surface has been created, we do no longer have to deal with platform specific code in Vulkan. Once we have a swapchain, we can obtain the Vulkan images in the swapchain.

uint32_t imageCount;
VK_CHECK(fpGetSwapchainImagesKHR(device, swapchain, &imageCount, nullptr));
swapchainImages.resize(imageCount);
VK_CHECK(fpGetSwapchainImagesKHR(device, swapchain, &imageCount, swapchainImages.data()));

For rendering to the screen, we will render to these images.

Rendering to Screen

Once the swapchain is alive, we will render to screen by acquiring the swapchain, rendering to the appropriate image, and release it.

unsigned image;
VkResult res = fpAcquireNextImageKHR(device, swapchain, UINT64_MAX, acquireSemaphore, VK_NULL_HANDLE, image);

We can now render to swapchainImages[image], and present it.

Result WSIPlatform::presentImage(unsigned index)
{
VkResult result;
VkPresentInfoKHR present = { VK_STRUCTURE_TYPE_PRESENT_INFO_KHR };
present.swapchainCount = 1;
present.pSwapchains = &swapchain;
present.pImageIndices = &index;
present.pResults = &result;
present.waitSemaphoreCount = 1;
present.pWaitSemaphores = &pContext->getSwapchainReleaseSemaphore();
VkResult res = fpQueuePresentKHR(queue, &present);
if (res == VK_SUBOPTIMAL_KHR || res == VK_ERROR_OUT_OF_DATE_KHR)
return RESULT_ERROR_OUTDATED_SWAPCHAIN;
else if (res != VK_SUCCESS)
return RESULT_ERROR_GENERIC;
else
return RESULT_SUCCESS;
}

Running the Main Loop in android_main

Once everything is initialized, we will drive our application from the main loop

void android_main(android_app *state)
{
// ...
for (;;)
{
while (ALooper_pollAll())
{
// Handle events
}
if (engine.pVulkanApp)
{
// Acquire next image
// Deal with outdated swapchain if needed
// Render
// Present
}
}
}

Dealing with Out-of-Date Swapchains

After acquiring a swapchain it is possible that the swapchain becomes outdated via error codes VK_SUBOPTIMAL_KHR and VK_ERROR_OUT_OF_DATE_KHR. This is possible if the surface has rotated or otherwise resized in any way. In this case, the swapchain must be recreated in order to obtain new VkImages for the backbuffers.

It is possible to recycle the old swapchain in this case.

VkSwapchainCreateInfoKHR info = { VK_STRUCTURE_TYPE_SWAPCHAIN_CREATE_INFO_KHR };
...
info.oldSwapchain = oldSwapchain;
VK_CHECK(fpCreateSwapchainKHR(device, &info, nullptr, &swapchain));
if (oldSwapchain != VK_NULL_HANDLE)
fpDestroySwapchainKHR(device, oldSwapchain, nullptr);