Add the MIN_UNDEQUEUED_BUFFERS query to ANW.

This change adds a new query to ANativeWindow for getting the minimum
number of buffers that must be left un-dequeued during the steady-state
operation of the ANativeWindow.

Change-Id: Ie8c461fc26b02ecde02ddb4f95bf763662cf1551
Related-Bug: 3356050

include/gui/SurfaceTexture.h

@@ -37,7 +37,8 @@ class IGraphicBufferAlloc;
 
 class SurfaceTexture : public BnSurfaceTexture {
 public:
-    enum { MIN_BUFFER_SLOTS = 3 };
+    enum { MIN_UNDEQUEUED_BUFFERS = 2 };
+    enum { MIN_BUFFER_SLOTS = MIN_UNDEQUEUED_BUFFERS + 1 };
     enum { NUM_BUFFER_SLOTS = 32 };
 
     struct FrameAvailableListener : public virtual RefBase {

include/gui/SurfaceTextureClient.h

@@ -40,40 +40,41 @@ private:
     SurfaceTextureClient(const SurfaceTextureClient& rhs);
 
     // ANativeWindow hooks
-    static int setSwapInterval(ANativeWindow* window, int interval);
-    static int dequeueBuffer(ANativeWindow* window, android_native_buffer_t** buffer);
     static int cancelBuffer(ANativeWindow* window, android_native_buffer_t* buffer);
+    static int dequeueBuffer(ANativeWindow* window, android_native_buffer_t** buffer);
     static int lockBuffer(ANativeWindow* window, android_native_buffer_t* buffer);
-    static int queueBuffer(ANativeWindow* window, android_native_buffer_t* buffer);
-    static int query(ANativeWindow* window, int what, int* value);
     static int perform(ANativeWindow* window, int operation, ...);
+    static int query(ANativeWindow* window, int what, int* value);
+    static int queueBuffer(ANativeWindow* window, android_native_buffer_t* buffer);
+    static int setSwapInterval(ANativeWindow* window, int interval);
 
-    int setSwapInterval(int interval);
+    int cancelBuffer(android_native_buffer_t* buffer);
     int dequeueBuffer(android_native_buffer_t** buffer);
     int lockBuffer(android_native_buffer_t* buffer);
-    int queueBuffer(android_native_buffer_t* buffer);
-    int cancelBuffer(android_native_buffer_t* buffer);
-    int query(int what, int* value);
     int perform(int operation, va_list args);
+    int query(int what, int* value);
+    int queueBuffer(android_native_buffer_t* buffer);
+    int setSwapInterval(int interval);
 
-    int dispatchSetUsage(va_list args);
     int dispatchConnect(va_list args);
     int dispatchDisconnect(va_list args);
-    int dispatchSetCrop(va_list args);
     int dispatchSetBufferCount(va_list args);
     int dispatchSetBuffersGeometry(va_list args);
     int dispatchSetBuffersTransform(va_list args);
+    int dispatchSetCrop(va_list args);
+    int dispatchSetUsage(va_list args);
 
     int connect(int api);
     int disconnect(int api);
-    int setUsage(uint32_t reqUsage);
-    int setCrop(Rect const* rect);
     int setBufferCount(int bufferCount);
     int setBuffersGeometry(int w, int h, int format);
     int setBuffersTransform(int transform);
+    int setCrop(Rect const* rect);
+    int setUsage(uint32_t reqUsage);
 
     void freeAllBuffers();
 
+    enum { MIN_UNDEQUEUED_BUFFERS = SurfaceTexture::MIN_UNDEQUEUED_BUFFERS };
     enum { MIN_BUFFER_SLOTS = SurfaceTexture::MIN_BUFFER_SLOTS };
     enum { NUM_BUFFER_SLOTS = SurfaceTexture::NUM_BUFFER_SLOTS };
     enum { DEFAULT_FORMAT = PIXEL_FORMAT_RGBA_8888 };

include/surfaceflinger/Surface.h

@@ -242,6 +242,10 @@ private:
     status_t validate(bool inCancelBuffer = false) const;
     sp<ISurface> getISurface() const;
 
+    // When the buffer pool is a fixed size we want to make sure SurfaceFlinger
+    // won't stall clients, so we require an extra buffer.
+    enum { MIN_UNDEQUEUED_BUFFERS = 2 };
+
     inline const GraphicBufferMapper& getBufferMapper() const { return mBufferMapper; }
     inline GraphicBufferMapper& getBufferMapper() { return mBufferMapper; }
 

include/ui/egl/android_natives.h

@@ -75,6 +75,26 @@ enum {
     NATIVE_WINDOW_WIDTH     = 0,
     NATIVE_WINDOW_HEIGHT,
     NATIVE_WINDOW_FORMAT,
+
+    /* The minimum number of buffers that must remain un-dequeued after a buffer
+     * has been queued.  This value applies only if set_buffer_count was used to
+     * override the number of buffers and if a buffer has since been queued.
+     * Users of the set_buffer_count ANativeWindow method should query this
+     * value before calling set_buffer_count.  If it is necessary to have N
+     * buffers simultaneously dequeued as part of the steady-state operation,
+     * and this query returns M then N+M buffers should be requested via
+     * native_window_set_buffer_count.
+     *
+     * Note that this value does NOT apply until a single buffer has been
+     * queued.  In particular this means that it is possible to:
+     *
+     * 1. Query M = min undequeued buffers
+     * 2. Set the buffer count to N + M
+     * 3. Dequeue all N + M buffers
+     * 4. Cancel M buffers
+     * 5. Queue, dequeue, queue, dequeue, ad infinitum
+     */
+    NATIVE_WINDOW_MIN_UNDEQUEUED_BUFFERS,
 };
 
 /* valid operations for the (*perform)() hook */

libs/gui/SurfaceTexture.cpp

@@ -96,6 +96,11 @@ SurfaceTexture::~SurfaceTexture() {
 
 status_t SurfaceTexture::setBufferCount(int bufferCount) {
     LOGV("SurfaceTexture::setBufferCount");
+
+    if (bufferCount < MIN_BUFFER_SLOTS) {
+        return BAD_VALUE;
+    }
+
     Mutex::Autolock lock(mMutex);
     freeAllBuffers();
     mBufferCount = bufferCount;

libs/gui/SurfaceTextureClient.cpp

@@ -143,8 +143,21 @@ int SurfaceTextureClient::queueBuffer(android_native_buffer_t* buffer) {
 int SurfaceTextureClient::query(int what, int* value) {
     LOGV("SurfaceTextureClient::query");
     Mutex::Autolock lock(mMutex);
-    // XXX: Implement this!
-    return INVALID_OPERATION;
+    switch (what) {
+    case NATIVE_WINDOW_WIDTH:
+    case NATIVE_WINDOW_HEIGHT:
+        // XXX: How should SurfaceTexture behave if setBuffersGeometry didn't
+        // override the size?
+        *value = 0;
+        return NO_ERROR;
+    case NATIVE_WINDOW_FORMAT:
+        *value = DEFAULT_FORMAT;
+        return NO_ERROR;
+    case NATIVE_WINDOW_MIN_UNDEQUEUED_BUFFERS:
+        *value = MIN_UNDEQUEUED_BUFFERS;
+        return NO_ERROR;
+    }
+    return BAD_VALUE;
 }
 
 int SurfaceTextureClient::perform(int operation, va_list args)

libs/surfaceflinger_client/Surface.cpp

@@ -709,6 +709,9 @@ int Surface::query(int what, int* value)
     case NATIVE_WINDOW_FORMAT:
         *value = int(mFormat);
         return NO_ERROR;
+    case NATIVE_WINDOW_MIN_UNDEQUEUED_BUFFERS:
+        *value = MIN_UNDEQUEUED_BUFFERS;
+        return NO_ERROR;
     }
     return BAD_VALUE;
 }