Use std::array type to describe and iterate over preferred HW accel

Using std::array simplifies iterating over the array. Still returning
arrays from functions is cumbersome. With adoption of C++20 to Qt we
can fix that with span.

Change-Id: Iadc43df8232361977dbcbe1ef000034de47cbeb5
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
Reviewed-by: Lars Knoll <lars@knoll.priv.no>
(cherry picked from commit 924500f42cf252f31631ae52d08cb99b028f90fb)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

3 files changed, 12 insertions, 20 deletions

diff --git a/src/plugins/multimedia/ffmpeg/qffmpeghwaccel.cpp b/src/plugins/multimedia/ffmpeg/qffmpeghwaccel.cpp
index 84d84ff12..e5d90239b 100644
--- a/src/plugins/multimedia/ffmpeg/qffmpeghwaccel.cpp
+++ b/src/plugins/multimedia/ffmpeg/qffmpeghwaccel.cpp
@@ -26,11 +26,7 @@ QT_BEGIN_NAMESPACE
 
 namespace QFFmpeg {
 
-// HW context initialization
-
-// preferred order of HW accelerators to use
 static const AVHWDeviceType preferredHardwareAccelerators[] = {
-// Linux/Unix
 #if defined(Q_OS_LINUX)
     AV_HWDEVICE_TYPE_VAAPI,
 //    AV_HWDEVICE_TYPE_DRM,
@@ -41,7 +37,6 @@ static const AVHWDeviceType preferredHardwareAccelerators[] = {
 #elif defined (Q_OS_ANDROID)
     AV_HWDEVICE_TYPE_MEDIACODEC,
 #endif
-    AV_HWDEVICE_TYPE_NONE
 };
 
 static AVBufferRef *loadHWContext(const AVHWDeviceType type)
@@ -63,20 +58,18 @@ static AVBufferRef *hardwareContextForCodec(const AVCodec *codec)
 
     // First try our preferred accelerators. Those are the ones where we can
     // set up a zero copy pipeline
-    auto *preferred = preferredHardwareAccelerators;
-    while (*preferred != AV_HWDEVICE_TYPE_NONE) {
+    for (auto type : preferredHardwareAccelerators) {
         for (int i = 0;; ++i) {
             const AVCodecHWConfig *config = avcodec_get_hw_config(codec, i);
             if (!config)
                 break;
-            if (config->device_type == *preferred) {
+            if (config->device_type == type) {
                 auto *hwContext = loadHWContext(config->device_type);
                 if (hwContext)
                     return hwContext;
                 break;
             }
         }
-        ++preferred;
     }
 
     // Ok, let's see if we can get any HW acceleration at all. It'll still involve one buffer copy,
@@ -174,9 +167,10 @@ AVPixelFormat HWAccel::format(AVFrame *frame)
     return AVPixelFormat(hwFramesContext->sw_format);
 }
 
-const AVHWDeviceType *HWAccel::preferredDeviceTypes()
+std::pair<const AVHWDeviceType*, qsizetype> HWAccel::preferredDeviceTypes()
 {
-    return preferredHardwareAccelerators;
+    return { preferredHardwareAccelerators,
+             sizeof(preferredHardwareAccelerators) / sizeof(AVHWDeviceType) };
 }
 
 AVHWDeviceContext *HWAccel::hwDeviceContext() const
@@ -289,12 +283,10 @@ const AVCodec *HWAccel::hardwareEncoderForCodecId(AVCodecID id) const
 
 std::unique_ptr<HWAccel> HWAccel::findHardwareAccelForCodecID(AVCodecID id)
 {
-    auto *accels = preferredHardwareAccelerators;
-    while (*accels != AV_HWDEVICE_TYPE_NONE) {
-        auto accel = HWAccel::create(*accels);
+    for (auto type : preferredHardwareAccelerators) {
+        auto accel = HWAccel::create(type);
         if (accel && accel->hardwareEncoderForCodecId(id))
             return accel;
-        ++accels;
     }
     return {};
 }
diff --git a/src/plugins/multimedia/ffmpeg/qffmpeghwaccel_p.h b/src/plugins/multimedia/ffmpeg/qffmpeghwaccel_p.h
index 7186d56ab..81bb163bb 100644
--- a/src/plugins/multimedia/ffmpeg/qffmpeghwaccel_p.h
+++ b/src/plugins/multimedia/ffmpeg/qffmpeghwaccel_p.h
@@ -106,7 +106,8 @@ public:
     AVHWFramesContext *hwFramesContext() const;
 
     static AVPixelFormat format(AVFrame *frame);
-    static const AVHWDeviceType *preferredDeviceTypes();
+    static std::pair<const AVHWDeviceType*, qsizetype> preferredDeviceTypes();
+
 private:
     HWAccel(AVBufferRef *hwDeviceContext, AVBufferRef *hwFrameContext = nullptr)
         : m_hwDeviceContext(hwDeviceContext), m_hwFramesContext(hwFrameContext)
diff --git a/src/plugins/multimedia/ffmpeg/qffmpegvideoframeencoder.cpp b/src/plugins/multimedia/ffmpeg/qffmpegvideoframeencoder.cpp
index ea2ed46d3..2a9438a00 100644
--- a/src/plugins/multimedia/ffmpeg/qffmpegvideoframeencoder.cpp
+++ b/src/plugins/multimedia/ffmpeg/qffmpegvideoframeencoder.cpp
@@ -46,10 +46,9 @@ VideoFrameEncoder::VideoFrameEncoder(const QMediaEncoderSettings &encoderSetting
     auto codecID = QFFmpegMediaFormatInfo::codecIdForVideoCodec(qVideoCodec);
 
 #ifndef QT_DISABLE_HW_ENCODING
-    const auto *accels = HWAccel::preferredDeviceTypes();
-    while (*accels != AV_HWDEVICE_TYPE_NONE) {
-        auto accel = HWAccel::create(*accels);
-        ++accels;
+    auto [preferredTypes, size] = HWAccel::preferredDeviceTypes();
+    for (qsizetype i = 0; i < size; i++) {
+        auto accel = HWAccel::create(preferredTypes[i]);
         if (!accel)
             continue;