rhi: Allow null resources in srb

In this case the srb represents the layout only, and can still be used
to create a pipeline. For setShaderResources() one will then need to use
another, layout compatible, srb that references valid resources.

Change-Id: I3ea5b63df3be8847540ca4c0c40fbd29dbed8fb7
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

4 files changed, 330 insertions, 68 deletions

diff --git a/src/gui/rhi/qrhi.cpp b/src/gui/rhi/qrhi.cpp
index c5fac634be..6627a459e3 100644
--- a/src/gui/rhi/qrhi.cpp
+++ b/src/gui/rhi/qrhi.cpp
@@ -2854,7 +2854,15 @@ bool QRhiShaderResourceBinding::isLayoutCompatible(const QRhiShaderResourceBindi
     \return a shader resource binding for the given binding number, pipeline
     stages, and buffer specified by \a binding, \a stage, and \a buf.
 
-    \note \a buf must have been created with QRhiBuffer::UniformBuffer.
+    \note When \a buf is not null, it must have been created with
+    QRhiBuffer::UniformBuffer.
+
+    \note \a buf can be null. It is valid to create a
+    QRhiShaderResourceBindings with unspecified resources, but such an object
+    cannot be used with QRhiCommandBuffer::setShaderResources(). It is however
+    suitable for creating pipelines. Such a pipeline must then always be used
+    together with another, layout compatible QRhiShaderResourceBindings with
+    resources present passed to QRhiCommandBuffer::setShaderResources().
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::uniformBuffer(
         int binding, StageFlags stage, QRhiBuffer *buf)
@@ -2880,7 +2888,15 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::uniformBuffer(
 
     \note \a size must be greater than 0.
 
-    \note \a buf must have been created with QRhiBuffer::UniformBuffer.
+    \note When \a buf is not null, it must have been created with
+    QRhiBuffer::UniformBuffer.
+
+    \note \a buf can be null. It is valid to create a
+    QRhiShaderResourceBindings with unspecified resources, but such an object
+    cannot be used with QRhiCommandBuffer::setShaderResources(). It is however
+    suitable for creating pipelines. Such a pipeline must then always be used
+    together with another, layout compatible QRhiShaderResourceBindings with
+    resources present passed to QRhiCommandBuffer::setShaderResources().
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::uniformBuffer(
         int binding, StageFlags stage, QRhiBuffer *buf, int offset, int size)
@@ -2901,7 +2917,15 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::uniformBuffer(
     size of the bound region is specified by \a size. Like with non-dynamic
     offsets, \c{offset + size} cannot exceed the size of \a buf.
 
-    \note \a buf must have been created with QRhiBuffer::UniformBuffer.
+    \note When \a buf is not null, it must have been created with
+    QRhiBuffer::UniformBuffer.
+
+    \note \a buf can be null. It is valid to create a
+    QRhiShaderResourceBindings with unspecified resources, but such an object
+    cannot be used with QRhiCommandBuffer::setShaderResources(). It is however
+    suitable for creating pipelines. Such a pipeline must then always be used
+    together with another, layout compatible QRhiShaderResourceBindings with
+    resources present passed to QRhiCommandBuffer::setShaderResources().
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::uniformBufferWithDynamicOffset(
         int binding, StageFlags stage, QRhiBuffer *buf, int size)
@@ -2919,6 +2943,13 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::uniformBufferWithDynamicOff
     \note This function is equivalent to calling sampledTextures() with a
     \c count of 1.
 
+    \note \a tex and \a sampler can be null. It is valid to create a
+    QRhiShaderResourceBindings with unspecified resources, but such an object
+    cannot be used with QRhiCommandBuffer::setShaderResources(). It is however
+    suitable for creating pipelines. Such a pipeline must then always be used
+    together with another, layout compatible QRhiShaderResourceBindings with
+    resources present passed to QRhiCommandBuffer::setShaderResources().
+
     \sa sampledTextures()
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::sampledTexture(
@@ -2953,6 +2984,13 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::sampledTexture(
     advised to provide "dummy" samplers and textures if some array elements are
     not relevant (due to not being accessed in the shader).
 
+    \note \a texSamplers can be null. It is valid to create a
+    QRhiShaderResourceBindings with unspecified resources, but such an object
+    cannot be used with QRhiCommandBuffer::setShaderResources(). It is however
+    suitable for creating pipelines. Such a pipeline must then always be used
+    together with another, layout compatible QRhiShaderResourceBindings with
+    resources present passed to QRhiCommandBuffer::setShaderResources().
+
     \sa sampledTexture()
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::sampledTextures(
@@ -2964,8 +3002,12 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::sampledTextures(
     b.d.stage = stage;
     b.d.type = SampledTexture;
     b.d.u.stex.count = count;
-    for (int i = 0; i < count; ++i)
-        b.d.u.stex.texSamplers[i] = texSamplers[i];
+    for (int i = 0; i < count; ++i) {
+        if (texSamplers)
+            b.d.u.stex.texSamplers[i] = texSamplers[i];
+        else
+            b.d.u.stex.texSamplers[i] = {};
+    }
     return b;
 }
 
@@ -2975,7 +3017,15 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::sampledTextures(
    will have access to all layers of the specified \a level. (so if the texture
    is a cubemap, the shader must use imageCube instead of image2D)
 
-   \note \a tex must have been created with QRhiTexture::UsedWithLoadStore.
+   \note When \a tex is not null, it must have been created with
+   QRhiTexture::UsedWithLoadStore.
+
+   \note \a tex can be null. It is valid to create a QRhiShaderResourceBindings
+   with unspecified resources, but such an object cannot be used with
+   QRhiCommandBuffer::setShaderResources(). It is however suitable for creating
+   pipelines. Such a pipeline must then always be used together with another,
+   layout compatible QRhiShaderResourceBindings with resources present passed
+   to QRhiCommandBuffer::setShaderResources().
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::imageLoad(
         int binding, StageFlags stage, QRhiTexture *tex, int level)
@@ -2995,7 +3045,15 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::imageLoad(
    will have access to all layers of the specified \a level. (so if the texture
    is a cubemap, the shader must use imageCube instead of image2D)
 
-   \note \a tex must have been created with QRhiTexture::UsedWithLoadStore.
+   \note When \a tex is not null, it must have been created with
+   QRhiTexture::UsedWithLoadStore.
+
+   \note \a tex can be null. It is valid to create a QRhiShaderResourceBindings
+   with unspecified resources, but such an object cannot be used with
+   QRhiCommandBuffer::setShaderResources(). It is however suitable for creating
+   pipelines. Such a pipeline must then always be used together with another,
+   layout compatible QRhiShaderResourceBindings with resources present passed
+   to QRhiCommandBuffer::setShaderResources().
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::imageStore(
         int binding, StageFlags stage, QRhiTexture *tex, int level)
@@ -3011,7 +3069,15 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::imageStore(
    will have access to all layers of the specified \a level. (so if the texture
    is a cubemap, the shader must use imageCube instead of image2D)
 
-   \note \a tex must have been created with QRhiTexture::UsedWithLoadStore.
+   \note When \a tex is not null, it must have been created with
+   QRhiTexture::UsedWithLoadStore.
+
+   \note \a tex can be null. It is valid to create a QRhiShaderResourceBindings
+   with unspecified resources, but such an object cannot be used with
+   QRhiCommandBuffer::setShaderResources(). It is however suitable for creating
+   pipelines. Such a pipeline must then always be used together with another,
+   layout compatible QRhiShaderResourceBindings with resources present passed
+   to QRhiCommandBuffer::setShaderResources().
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::imageLoadStore(
         int binding, StageFlags stage, QRhiTexture *tex, int level)
@@ -3025,7 +3091,15 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::imageLoadStore(
     \return a shader resource binding for a read-only storage buffer with the
     given \a binding number and pipeline \a stage.
 
-    \note \a buf must have been created with QRhiBuffer::StorageBuffer.
+    \note When \a buf is not null, must have been created with
+    QRhiBuffer::StorageBuffer.
+
+    \note \a buf can be null. It is valid to create a
+    QRhiShaderResourceBindings with unspecified resources, but such an object
+    cannot be used with QRhiCommandBuffer::setShaderResources(). It is however
+    suitable for creating pipelines. Such a pipeline must then always be used
+    together with another, layout compatible QRhiShaderResourceBindings with
+    resources present passed to QRhiCommandBuffer::setShaderResources().
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::bufferLoad(
         int binding, StageFlags stage, QRhiBuffer *buf)
@@ -3045,7 +3119,15 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::bufferLoad(
     given \a binding number and pipeline \a stage. This overload binds a region
     only, as specified by \a offset and \a size.
 
-    \note \a buf must have been created with QRhiBuffer::StorageBuffer.
+    \note When \a buf is not null, must have been created with
+    QRhiBuffer::StorageBuffer.
+
+    \note \a buf can be null. It is valid to create a
+    QRhiShaderResourceBindings with unspecified resources, but such an object
+    cannot be used with QRhiCommandBuffer::setShaderResources(). It is however
+    suitable for creating pipelines. Such a pipeline must then always be used
+    together with another, layout compatible QRhiShaderResourceBindings with
+    resources present passed to QRhiCommandBuffer::setShaderResources().
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::bufferLoad(
         int binding, StageFlags stage, QRhiBuffer *buf, int offset, int size)
@@ -3061,7 +3143,15 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::bufferLoad(
     \return a shader resource binding for a write-only storage buffer with the
     given \a binding number and pipeline \a stage.
 
-    \note \a buf must have been created with QRhiBuffer::StorageBuffer.
+    \note When \a buf is not null, must have been created with
+    QRhiBuffer::StorageBuffer.
+
+    \note \a buf can be null. It is valid to create a
+    QRhiShaderResourceBindings with unspecified resources, but such an object
+    cannot be used with QRhiCommandBuffer::setShaderResources(). It is however
+    suitable for creating pipelines. Such a pipeline must then always be used
+    together with another, layout compatible QRhiShaderResourceBindings with
+    resources present passed to QRhiCommandBuffer::setShaderResources().
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::bufferStore(
         int binding, StageFlags stage, QRhiBuffer *buf)
@@ -3076,7 +3166,15 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::bufferStore(
     given \a binding number and pipeline \a stage. This overload binds a region
     only, as specified by \a offset and \a size.
 
-    \note \a buf must have been created with QRhiBuffer::StorageBuffer.
+    \note When \a buf is not null, must have been created with
+    QRhiBuffer::StorageBuffer.
+
+    \note \a buf can be null. It is valid to create a
+    QRhiShaderResourceBindings with unspecified resources, but such an object
+    cannot be used with QRhiCommandBuffer::setShaderResources(). It is however
+    suitable for creating pipelines. Such a pipeline must then always be used
+    together with another, layout compatible QRhiShaderResourceBindings with
+    resources present passed to QRhiCommandBuffer::setShaderResources().
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::bufferStore(
         int binding, StageFlags stage, QRhiBuffer *buf, int offset, int size)
@@ -3092,7 +3190,15 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::bufferStore(
     \return a shader resource binding for a read-write storage buffer with the
     given \a binding number and pipeline \a stage.
 
-    \note \a buf must have been created with QRhiBuffer::StorageBuffer.
+    \note When \a buf is not null, must have been created with
+    QRhiBuffer::StorageBuffer.
+
+    \note \a buf can be null. It is valid to create a
+    QRhiShaderResourceBindings with unspecified resources, but such an object
+    cannot be used with QRhiCommandBuffer::setShaderResources(). It is however
+    suitable for creating pipelines. Such a pipeline must then always be used
+    together with another, layout compatible QRhiShaderResourceBindings with
+    resources present passed to QRhiCommandBuffer::setShaderResources().
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::bufferLoadStore(
         int binding, StageFlags stage, QRhiBuffer *buf)
@@ -3107,7 +3213,15 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::bufferLoadStore(
     given \a binding number and pipeline \a stage. This overload binds a region
     only, as specified by \a offset and \a size.
 
-    \note \a buf must have been created with QRhiBuffer::StorageBuffer.
+    \note When \a buf is not null, must have been created with
+    QRhiBuffer::StorageBuffer.
+
+    \note \a buf can be null. It is valid to create a
+    QRhiShaderResourceBindings with unspecified resources, but such an object
+    cannot be used with QRhiCommandBuffer::setShaderResources(). It is however
+    suitable for creating pipelines. Such a pipeline must then always be used
+    together with another, layout compatible QRhiShaderResourceBindings with
+    resources present passed to QRhiCommandBuffer::setShaderResources().
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::bufferLoadStore(
         int binding, StageFlags stage, QRhiBuffer *buf, int offset, int size)
diff --git a/src/gui/rhi/qrhimetal.mm b/src/gui/rhi/qrhimetal.mm
index ee7735c1bb..d9575e949b 100644
--- a/src/gui/rhi/qrhimetal.mm
+++ b/src/gui/rhi/qrhimetal.mm
@@ -3006,54 +3006,8 @@ bool QMetalShaderResourceBindings::create()
 
     boundResourceData.resize(sortedBindings.count());
 
-    for (int i = 0, ie = sortedBindings.count(); i != ie; ++i) {
-        const QRhiShaderResourceBinding::Data *b = sortedBindings.at(i).data();
-        QMetalShaderResourceBindings::BoundResourceData &bd(boundResourceData[i]);
-        switch (b->type) {
-        case QRhiShaderResourceBinding::UniformBuffer:
-        {
-            QMetalBuffer *bufD = QRHI_RES(QMetalBuffer, b->u.ubuf.buf);
-            bd.ubuf.id = bufD->m_id;
-            bd.ubuf.generation = bufD->generation;
-        }
-            break;
-        case QRhiShaderResourceBinding::SampledTexture:
-        {
-            const QRhiShaderResourceBinding::Data::SampledTextureData *data = &b->u.stex;
-            bd.stex.count = data->count;
-            for (int elem = 0; elem < data->count; ++elem) {
-                QMetalTexture *texD = QRHI_RES(QMetalTexture, data->texSamplers[elem].tex);
-                QMetalSampler *samplerD = QRHI_RES(QMetalSampler, data->texSamplers[elem].sampler);
-                bd.stex.d[elem].texId = texD->m_id;
-                bd.stex.d[elem].texGeneration = texD->generation;
-                bd.stex.d[elem].samplerId = samplerD->m_id;
-                bd.stex.d[elem].samplerGeneration = samplerD->generation;
-            }
-        }
-            break;
-        case QRhiShaderResourceBinding::ImageLoad:
-        case QRhiShaderResourceBinding::ImageStore:
-        case QRhiShaderResourceBinding::ImageLoadStore:
-        {
-            QMetalTexture *texD = QRHI_RES(QMetalTexture, b->u.simage.tex);
-            bd.simage.id = texD->m_id;
-            bd.simage.generation = texD->generation;
-        }
-            break;
-        case QRhiShaderResourceBinding::BufferLoad:
-        case QRhiShaderResourceBinding::BufferStore:
-        case QRhiShaderResourceBinding::BufferLoadStore:
-        {
-            QMetalBuffer *bufD = QRHI_RES(QMetalBuffer, b->u.sbuf.buf);
-            bd.sbuf.id = bufD->m_id;
-            bd.sbuf.generation = bufD->generation;
-        }
-            break;
-        default:
-            Q_UNREACHABLE();
-            break;
-        }
-    }
+    for (BoundResourceData &bd : boundResourceData)
+        memset(&bd, 0, sizeof(BoundResourceData));
 
     generation += 1;
     return true;
diff --git a/src/gui/rhi/qrhivulkan.cpp b/src/gui/rhi/qrhivulkan.cpp
index 4bf859a716..46a6146f20 100644
--- a/src/gui/rhi/qrhivulkan.cpp
+++ b/src/gui/rhi/qrhivulkan.cpp
@@ -2555,7 +2555,6 @@ void QRhiVulkan::updateShaderResourceBindings(QRhiShaderResourceBindings *srb, i
     const bool updateAll = descSetIdx < 0;
     int frameSlot = updateAll ? 0 : descSetIdx;
     while (frameSlot < (updateAll ? QVK_FRAMES_IN_FLIGHT : descSetIdx + 1)) {
-        srbD->boundResourceData[frameSlot].resize(srbD->sortedBindings.count());
         for (int i = 0, ie = srbD->sortedBindings.count(); i != ie; ++i) {
             const QRhiShaderResourceBinding::Data *b = srbD->sortedBindings.at(i).data();
             QVkShaderResourceBindings::BoundResourceData &bd(srbD->boundResourceData[frameSlot][i]);
@@ -6188,7 +6187,11 @@ bool QVkShaderResourceBindings::create()
     if (!rhiD->allocateDescriptorSet(&allocInfo, descSets, &poolIndex))
         return false;
 
-    rhiD->updateShaderResourceBindings(this);
+    for (int i = 0; i < QVK_FRAMES_IN_FLIGHT; ++i) {
+        boundResourceData[i].resize(sortedBindings.count());
+        for (BoundResourceData &bd : boundResourceData[i])
+            memset(&bd, 0, sizeof(BoundResourceData));
+    }
 
     lastActiveFrameSlot = -1;
     generation += 1;
diff --git a/tests/auto/gui/rhi/qrhi/tst_qrhi.cpp b/tests/auto/gui/rhi/qrhi/tst_qrhi.cpp
index f559b40cf6..ee14116e1c 100644
--- a/tests/auto/gui/rhi/qrhi/tst_qrhi.cpp
+++ b/tests/auto/gui/rhi/qrhi/tst_qrhi.cpp
@@ -91,6 +91,13 @@ private slots:
     void resourceUpdateBatchRGBATextureMip();
     void invalidPipeline_data();
     void invalidPipeline();
+    void srbLayoutCompatibility_data();
+    void srbLayoutCompatibility();
+    void srbWithNoResource_data();
+    void srbWithNoResource();
+    void renderPassDescriptorCompatibility_data();
+    void renderPassDescriptorCompatibility();
+
     void renderToTextureSimple_data();
     void renderToTextureSimple();
     void renderToTextureMip_data();
@@ -103,14 +110,12 @@ private slots:
     void renderToTextureArrayOfTexturedQuad();
     void renderToTextureTexturedQuadAndUniformBuffer_data();
     void renderToTextureTexturedQuadAndUniformBuffer();
+    void renderToTextureDeferredSrb_data();
+    void renderToTextureDeferredSrb();
     void renderToWindowSimple_data();
     void renderToWindowSimple();
     void finishWithinSwapchainFrame_data();
     void finishWithinSwapchainFrame();
-    void srbLayoutCompatibility_data();
-    void srbLayoutCompatibility();
-    void renderPassDescriptorCompatibility_data();
-    void renderPassDescriptorCompatibility();
 
 private:
     void setWindowType(QWindow *window, QRhi::Implementation impl);
@@ -2212,6 +2217,150 @@ void tst_QRhi::renderToTextureTexturedQuadAndUniformBuffer()
     QCOMPARE(result1.pixel(28, 178), empty);
 }
 
+void tst_QRhi::renderToTextureDeferredSrb_data()
+{
+    rhiTestData();
+}
+
+void tst_QRhi::renderToTextureDeferredSrb()
+{
+    QFETCH(QRhi::Implementation, impl);
+    QFETCH(QRhiInitParams *, initParams);
+
+    QScopedPointer<QRhi> rhi(QRhi::create(impl, initParams, QRhi::Flags(), nullptr));
+    if (!rhi)
+        QSKIP("QRhi could not be created, skipping testing rendering");
+
+    QImage inputImage;
+    inputImage.load(QLatin1String(":/data/qt256.png"));
+    QVERIFY(!inputImage.isNull());
+
+    QScopedPointer<QRhiTexture> texture(rhi->newTexture(QRhiTexture::RGBA8, inputImage.size(), 1,
+                                                        QRhiTexture::RenderTarget | QRhiTexture::UsedAsTransferSource));
+    QVERIFY(texture->create());
+
+    QScopedPointer<QRhiTextureRenderTarget> rt(rhi->newTextureRenderTarget({ texture.data() }));
+    QScopedPointer<QRhiRenderPassDescriptor> rpDesc(rt->newCompatibleRenderPassDescriptor());
+    rt->setRenderPassDescriptor(rpDesc.data());
+    QVERIFY(rt->create());
+
+    QRhiCommandBuffer *cb = nullptr;
+    QVERIFY(rhi->beginOffscreenFrame(&cb) == QRhi::FrameOpSuccess);
+    QVERIFY(cb);
+
+    QRhiResourceUpdateBatch *updates = rhi->nextResourceUpdateBatch();
+
+    static const float verticesUvs[] = {
+        -1.0f, -1.0f,   0.0f, 0.0f,
+        1.0f, -1.0f,    1.0f, 0.0f,
+        -1.0f, 1.0f,    0.0f, 1.0f,
+        1.0f, 1.0f,     1.0f, 1.0f
+    };
+    QScopedPointer<QRhiBuffer> vbuf(rhi->newBuffer(QRhiBuffer::Immutable, QRhiBuffer::VertexBuffer, sizeof(verticesUvs)));
+    QVERIFY(vbuf->create());
+    updates->uploadStaticBuffer(vbuf.data(), verticesUvs);
+
+    QScopedPointer<QRhiTexture> inputTexture(rhi->newTexture(QRhiTexture::RGBA8, inputImage.size()));
+    QVERIFY(inputTexture->create());
+    updates->uploadTexture(inputTexture.data(), inputImage);
+
+    QScopedPointer<QRhiSampler> sampler(rhi->newSampler(QRhiSampler::Nearest, QRhiSampler::Nearest, QRhiSampler::None,
+                                                        QRhiSampler::ClampToEdge, QRhiSampler::ClampToEdge));
+    QVERIFY(sampler->create());
+
+    QScopedPointer<QRhiBuffer> ubuf(rhi->newBuffer(QRhiBuffer::Dynamic, QRhiBuffer::UniformBuffer, 64 + 4));
+    QVERIFY(ubuf->create());
+
+    QMatrix4x4 matrix;
+    updates->updateDynamicBuffer(ubuf.data(), 0, 64, matrix.constData());
+    float opacity = 0.5f;
+    updates->updateDynamicBuffer(ubuf.data(), 64, 4, &opacity);
+
+    // this is the specific thing to test here: an srb with null resources
+    const QRhiShaderResourceBinding::StageFlags commonVisibility = QRhiShaderResourceBinding::VertexStage | QRhiShaderResourceBinding::FragmentStage;
+    QScopedPointer<QRhiShaderResourceBindings> layoutOnlySrb(rhi->newShaderResourceBindings());
+    layoutOnlySrb->setBindings({
+                         QRhiShaderResourceBinding::uniformBuffer(0, commonVisibility, nullptr),
+                         QRhiShaderResourceBinding::sampledTexture(1, QRhiShaderResourceBinding::FragmentStage, nullptr, nullptr)
+                     });
+    QVERIFY(layoutOnlySrb->create());
+
+    QScopedPointer<QRhiGraphicsPipeline> pipeline(rhi->newGraphicsPipeline());
+    pipeline->setTopology(QRhiGraphicsPipeline::TriangleStrip);
+    QShader vs = loadShader(":/data/textured.vert.qsb");
+    QVERIFY(vs.isValid());
+    QShader fs = loadShader(":/data/textured.frag.qsb");
+    QVERIFY(fs.isValid());
+    pipeline->setShaderStages({ { QRhiShaderStage::Vertex, vs }, { QRhiShaderStage::Fragment, fs } });
+    QRhiVertexInputLayout inputLayout;
+    inputLayout.setBindings({ { 4 * sizeof(float) } });
+    inputLayout.setAttributes({
+                                  { 0, 0, QRhiVertexInputAttribute::Float2, 0 },
+                                  { 0, 1, QRhiVertexInputAttribute::Float2, 2 * sizeof(float) }
+                              });
+    pipeline->setVertexInputLayout(inputLayout);
+    pipeline->setShaderResourceBindings(layoutOnlySrb.data()); // no resources needed yet
+    pipeline->setRenderPassDescriptor(rpDesc.data());
+
+    QVERIFY(pipeline->create());
+
+    // another, layout compatible, srb with the actual resources
+    QScopedPointer<QRhiShaderResourceBindings> layoutCompatibleSrbWithResources(rhi->newShaderResourceBindings());
+    layoutCompatibleSrbWithResources->setBindings({
+                         QRhiShaderResourceBinding::uniformBuffer(0, commonVisibility, ubuf.data()),
+                         QRhiShaderResourceBinding::sampledTexture(1, QRhiShaderResourceBinding::FragmentStage, inputTexture.data(), sampler.data())
+                     });
+    QVERIFY(layoutCompatibleSrbWithResources->create());
+
+    cb->beginPass(rt.data(), Qt::black, { 1.0f, 0 }, updates);
+    cb->setGraphicsPipeline(pipeline.data());
+    cb->setShaderResources(layoutCompatibleSrbWithResources.data()); // here we must use the srb referencing the resources
+    cb->setViewport({ 0, 0, float(texture->pixelSize().width()), float(texture->pixelSize().height()) });
+    QRhiCommandBuffer::VertexInput vbindings(vbuf.data(), 0);
+    cb->setVertexInput(0, 1, &vbindings);
+    cb->draw(4);
+
+    QRhiReadbackResult readResult;
+    QImage result;
+    readResult.completed = [&readResult, &result] {
+        result = QImage(reinterpret_cast<const uchar *>(readResult.data.constData()),
+                        readResult.pixelSize.width(), readResult.pixelSize.height(),
+                        QImage::Format_RGBA8888_Premultiplied);
+    };
+    QRhiResourceUpdateBatch *readbackBatch = rhi->nextResourceUpdateBatch();
+    readbackBatch->readBackTexture({ texture.data() }, &readResult);
+    cb->endPass(readbackBatch);
+
+    rhi->endOffscreenFrame();
+
+    QVERIFY(!result.isNull());
+
+    if (impl == QRhi::Null)
+        return;
+
+    if (rhi->isYUpInFramebuffer() != rhi->isYUpInNDC())
+        result = std::move(result).mirrored();
+
+    // opacity 0.5 (premultiplied)
+    static const auto checkSemiWhite = [](const QRgb &c) {
+        QRgb semiWhite127 = qPremultiply(qRgba(255, 255, 255, 127));
+        QRgb semiWhite128 = qPremultiply(qRgba(255, 255, 255, 128));
+        return c == semiWhite127 || c == semiWhite128;
+    };
+    QVERIFY(checkSemiWhite(result.pixel(79, 77)));
+    QVERIFY(checkSemiWhite(result.pixel(124, 81)));
+    QVERIFY(checkSemiWhite(result.pixel(128, 149)));
+    QVERIFY(checkSemiWhite(result.pixel(120, 189)));
+    QVERIFY(checkSemiWhite(result.pixel(116, 185)));
+    QVERIFY(checkSemiWhite(result.pixel(191, 172)));
+
+    QRgb empty = qRgba(0, 0, 0, 0);
+    QCOMPARE(result.pixel(11, 45), empty);
+    QCOMPARE(result.pixel(246, 202), empty);
+    QCOMPARE(result.pixel(130, 18), empty);
+    QCOMPARE(result.pixel(4, 227), empty);
+}
+
 void tst_QRhi::setWindowType(QWindow *window, QRhi::Implementation impl)
 {
     switch (impl) {
@@ -2630,6 +2779,48 @@ void tst_QRhi::srbLayoutCompatibility()
     }
 }
 
+void tst_QRhi::srbWithNoResource_data()
+{
+    rhiTestData();
+}
+
+void tst_QRhi::srbWithNoResource()
+{
+    QFETCH(QRhi::Implementation, impl);
+    QFETCH(QRhiInitParams *, initParams);
+
+    QScopedPointer<QRhi> rhi(QRhi::create(impl, initParams, QRhi::Flags(), nullptr));
+    if (!rhi)
+        QSKIP("QRhi could not be created, skipping testing srb");
+
+    QScopedPointer<QRhiTexture> texture(rhi->newTexture(QRhiTexture::RGBA8, QSize(512, 512)));
+    QVERIFY(texture->create());
+    QScopedPointer<QRhiSampler> sampler(rhi->newSampler(QRhiSampler::Nearest, QRhiSampler::Nearest, QRhiSampler::None,
+                                                        QRhiSampler::ClampToEdge, QRhiSampler::ClampToEdge));
+    QVERIFY(sampler->create());
+    QScopedPointer<QRhiBuffer> buf(rhi->newBuffer(QRhiBuffer::Dynamic, QRhiBuffer::UniformBuffer, 1024));
+    QVERIFY(buf->create());
+
+    {
+        QScopedPointer<QRhiShaderResourceBindings> srb1(rhi->newShaderResourceBindings());
+        srb1->setBindings({
+                             QRhiShaderResourceBinding::uniformBuffer(0, QRhiShaderResourceBinding::VertexStage, nullptr),
+                             QRhiShaderResourceBinding::sampledTexture(1, QRhiShaderResourceBinding::FragmentStage, nullptr, nullptr)
+                         });
+        QVERIFY(srb1->create());
+
+        QScopedPointer<QRhiShaderResourceBindings> srb2(rhi->newShaderResourceBindings());
+        srb2->setBindings({
+                             QRhiShaderResourceBinding::uniformBuffer(0, QRhiShaderResourceBinding::VertexStage, buf.data()),
+                             QRhiShaderResourceBinding::sampledTexture(1, QRhiShaderResourceBinding::FragmentStage, texture.data(), sampler.data())
+                         });
+        QVERIFY(srb2->create());
+
+        QVERIFY(srb1->isLayoutCompatible(srb2.data()));
+        QVERIFY(srb2->isLayoutCompatible(srb1.data()));
+    }
+}
+
 void tst_QRhi::renderPassDescriptorCompatibility_data()
 {
     rhiTestData();