QRhiBuffer Class

QRhiBuffer *ubuf = rhi->newBuffer(QRhiBuffer::Dynamic, QRhiBuffer::UniformBuffer, 64);
if (!ubuf->create()) { error(); }
QRhiResourceUpdateBatch *batch = rhi->nextResourceUpdateBatch();
QMatrix4x4 mvp;
// ... set up the modelview-projection matrix
batch->updateDynamicBuffer(ubuf, 0, 64, mvp.constData());
// ...
commandBuffer->resourceUpdate(batch); // or, alternatively, pass 'batch' to a beginPass() call

const float vertices[] = { -1.0f, -1.0f, 1.0f, -1.0f, 0.0f, 1.0f };
QRhiBuffer *vbuf = rhi->newBuffer(QRhiBuffer::Immutable, QRhiBuffer::VertexBuffer, sizeof(vertices));
if (!vbuf->create()) { error(); }
QRhiResourceUpdateBatch *batch = rhi->nextResourceUpdateBatch();
batch->uploadStaticBuffer(vbuf, vertices);
// ...
commandBuffer->resourceUpdate(batch); // or, alternatively, pass 'batch' to a beginPass() call

static const quint16 indices[] = { 0, 1, 2 };
QRhiBuffer *ibuf = rhi->newBuffer(QRhiBuffer::Immutable, QRhiBuffer::IndexBuffer, sizeof(indices));
if (!ibuf->create()) { error(); }
QRhiResourceUpdateBatch *batch = rhi->nextResourceUpdateBatch();
batch->uploadStaticBuffer(ibuf, indices);
// ...
commandBuffer->resourceUpdate(batch); // or, alternatively, pass 'batch' to a beginPass() call

if (buf->size() < newSize) {
    buf->setSize(newSize);
    if (!buf->create()) { error(); }
}
// continue using buf, fill it with new data

const int N = 2;
const int UB_SIZE = 64 + 4; // assuming a uniform block with { mat4 matrix; float opacity; }
const int ONE_UBUF_SIZE = rhi->ubufAligned(UB_SIZE);
const int TOTAL_UBUF_SIZE = N * ONE_UBUF_SIZE;
QRhiBuffer *ubuf = rhi->newBuffer(QRhiBuffer::Dynamic, QRhiBuffer::UniformBuffer, TOTAL_UBUF_SIZE);
if (!ubuf->create()) { error(); }
QRhiResourceUpdateBatch *batch = rhi->nextResourceUpdateBatch();
for (int i = 0; i < N; ++i) {
    batch->updateDynamicBuffer(ubuf, i * ONE_UBUF_SIZE, 64, matrix.constData());
    batch->updateDynamicBuffer(ubuf, i * ONE_UBUF_SIZE + 64, 4, &opacity);
}
// ...
// beginPass(), set pipeline, etc., and then:
for (int i = 0; i < N; ++i) {
    QRhiCommandBuffer::DynamicOffset dynOfs[] = { { 0, i * ONE_UBUF_SIZE } };
    cb->setShaderResources(srb, 1, dynOfs);
    cb->draw(36);
}

Member Function Documentation

[virtual] char *QRhiBuffer::beginFullDynamicBufferUpdateForCurrentFrame()

Returns a pointer to a memory block with the host visible buffer data.

This is a shortcut for medium-to-large dynamic uniform buffers that have their entire contents (or at least all regions that are read by the shaders in the current frame) changed in every frame and the QRhiResourceUpdateBatch-based update mechanism is seen too heavy due to the amount of data copying involved.

The call to this function must be eventually followed by a call to endFullDynamicUniformBufferUpdateForCurrentFrame(), before recording any render or compute pass that relies on this buffer.

[pure virtual] bool QRhiBuffer::create()

Creates the corresponding native graphics resources. If there are already resources present due to an earlier create() with no corresponding destroy(), then destroy() is called implicitly first.

Returns true when successful, false when a graphics operation failed. Regardless of the return value, calling destroy() is always safe.

[virtual] void QRhiBuffer::endFullDynamicBufferUpdateForCurrentFrame()

To be called when the entire contents of the buffer data has been updated in the memory block returned from beginFullDynamicBufferUpdateForCurrentFrame().

[virtual] QRhiBuffer::NativeBuffer QRhiBuffer::nativeBuffer()

Returns the underlying native resources for this buffer. The returned value will be empty if exposing the underlying native resources is not supported by the backend.

A QRhiBuffer may be backed by multiple native buffer objects, depending on the type() and the QRhi backend in use. When this is the case, all of them are returned in the objects array in the returned struct, with slotCount specifying the number of native buffer objects. While recording a frame, QRhi::currentFrameSlot() can be used to determine which of the native buffers QRhi is using for operations that read or write from this QRhiBuffer within the frame being recorded.

In some cases a QRhiBuffer will not be backed by a native buffer object at all. In this case slotCount will be set to 0 and no valid native objects are returned. This is not an error, and is perfectly valid when a given backend does not use native buffers for QRhiBuffers with certain types or usages.

See also QRhi::currentFrameSlot() and QRhi::FramesInFlight.

[override virtual] QRhiResource::Type QRhiBuffer::resourceType() const

Reimplements: QRhiResource::resourceType() const.

Returns the resource type.

void QRhiBuffer::setSize(quint32 sz)

Sets the size of the buffer in bytes. The size is normally specified in QRhi::newBuffer() so this function is only used when the size has to be changed. As with other setters, the size only takes effect when calling create(), and for already created buffers this involves releasing the previous native resource and creating new ones under the hood.

Backends may choose to allocate buffers bigger than sz in order to fulfill alignment requirements. This is hidden from the applications and size() will always report the size requested in sz.

See also size().

void QRhiBuffer::setType(QRhiBuffer::Type t)

Sets the buffer's type to t.

See also type().

void QRhiBuffer::setUsage(QRhiBuffer::UsageFlags u)

Sets the buffer's usage flags to u.

See also usage().

quint32 QRhiBuffer::size() const

Returns the buffer's size in bytes.

This is always the value that was passed to setSize() or QRhi::newBuffer(). Internally, the native buffers may be bigger if that is required by the underlying graphics API.

See also setSize().

QRhiBuffer::Type QRhiBuffer::type() const

Returns the buffer type.

See also setType().

QRhiBuffer::UsageFlags QRhiBuffer::usage() const

Returns the buffer's usage flags.

See also setUsage().