rhi: Report an "optimal capacity" from res.update batches

Change-Id: If47eddf3fe7d365c80b0a15712ef155a6898d904
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

3 files changed, 30 insertions, 2 deletions

diff --git a/src/gui/rhi/qrhi.cpp b/src/gui/rhi/qrhi.cpp
index f61fa6df59..a74765758c 100644
--- a/src/gui/rhi/qrhi.cpp
+++ b/src/gui/rhi/qrhi.cpp
@@ -4733,6 +4733,24 @@ void QRhiResourceUpdateBatch::merge(QRhiResourceUpdateBatch *other)
 }
 
 /*!
+    \return true until the number of buffer and texture operations enqueued
+    onto this batch is below a reasonable limit.
+
+    The return value is false when the number of buffer and/or texture
+    operations added to this batch have reached, or are about to reach, a
+    certain limit. The batch is fully functional afterwards as well, but may
+    need to allocate additional memory. Therefore, a renderer that collects
+    lots of buffer and texture updates in a single batch when preparing a frame
+    may want to consider \l{QRhiCommandBuffer::resourceUpdate()}{submitting the
+    batch} and \l{QRhi::nextResourceUpdateBatch()}{starting a new one} when
+    this function returns false.
+ */
+bool QRhiResourceUpdateBatch::hasOptimalCapacity() const
+{
+    return d->hasOptimalCapacity();
+}
+
+/*!
     Enqueues updating a region of a QRhiBuffer \a buf created with the type
     QRhiBuffer::Dynamic.
 
@@ -4997,6 +5015,12 @@ void QRhiResourceUpdateBatchPrivate::merge(QRhiResourceUpdateBatchPrivate *other
         textureOps.append(op);
 }
 
+bool QRhiResourceUpdateBatchPrivate::hasOptimalCapacity() const
+{
+    return bufferOps.count() < BUFFER_OPS_STATIC_ALLOC - 16
+            && textureOps.count() < TEXTURE_OPS_STATIC_ALLOC - 16;
+}
+
 /*!
     Sometimes committing resource updates is necessary without starting a
     render pass. Not often needed, updates should typically be passed to
diff --git a/src/gui/rhi/qrhi_p.h b/src/gui/rhi/qrhi_p.h
index d8e54fc9aa..1e86cbc04a 100644
--- a/src/gui/rhi/qrhi_p.h
+++ b/src/gui/rhi/qrhi_p.h
@@ -1403,6 +1403,7 @@ public:
     void release();
 
     void merge(QRhiResourceUpdateBatch *other);
+    bool hasOptimalCapacity() const;
 
     void updateDynamicBuffer(QRhiBuffer *buf, int offset, int size, const void *data);
     void uploadStaticBuffer(QRhiBuffer *buf, int offset, int size, const void *data);
diff --git a/src/gui/rhi/qrhi_p_p.h b/src/gui/rhi/qrhi_p_p.h
index ef27be6d7d..7fadcfcc1e 100644
--- a/src/gui/rhi/qrhi_p_p.h
+++ b/src/gui/rhi/qrhi_p_p.h
@@ -383,8 +383,10 @@ public:
         }
     };
 
-    QVarLengthArray<BufferOp, 1024> bufferOps;
-    QVarLengthArray<TextureOp, 256> textureOps;
+    static const int BUFFER_OPS_STATIC_ALLOC = 1024;
+    QVarLengthArray<BufferOp, BUFFER_OPS_STATIC_ALLOC> bufferOps;
+    static const int TEXTURE_OPS_STATIC_ALLOC = 256;
+    QVarLengthArray<TextureOp, TEXTURE_OPS_STATIC_ALLOC> textureOps;
 
     QRhiResourceUpdateBatch *q = nullptr;
     QRhiImplementation *rhi = nullptr;
@@ -392,6 +394,7 @@ public:
 
     void free();
     void merge(QRhiResourceUpdateBatchPrivate *other);
+    bool hasOptimalCapacity() const;
 
     static QRhiResourceUpdateBatchPrivate *get(QRhiResourceUpdateBatch *b) { return b->d; }
 };