QRhiShaderResourceBindings Class

Detailed Description

Encapsulates resources for making buffer, texture, sampler resources visible to shaders.

A QRhiShaderResourceBindings is a collection of QRhiShaderResourceBinding objects, each of which describe a single binding.

Take a fragment shader with the following interface:

  layout(std140, binding = 0) uniform buf {
      mat4 mvp;
      int flip;
  } ubuf;

  layout(binding = 1) uniform sampler2D tex;

To make resources visible to the shader, the following QRhiShaderResourceBindings could be created and then passed to QRhiGraphicsPipeline::setShaderResourceBindings():

  srb = rhi->newShaderResourceBindings();
  srb->setBindings({
      QRhiShaderResourceBinding::uniformBuffer(0, QRhiShaderResourceBinding::VertexStage | QRhiShaderResourceBinding::FragmentStage, ubuf),
      QRhiShaderResourceBinding::sampledTexture(1, QRhiShaderResourceBinding::FragmentStage, texture, sampler)
  });
  srb->build();
  ...
  ps = rhi->newGraphicsPipeline();
  ...
  ps->setShaderResourceBindings(srb);
  ps->build();
  ...
  cb->setGraphicsPipeline(ps);
  cb->setShaderResources(); // binds srb

This assumes that ubuf is a QRhiBuffer, texture is a QRhiTexture, while sampler is a QRhiSampler. The example also assumes that the uniform block is present in the vertex shader as well so the same buffer is made visible to the vertex stage too.

Advanced usage

Building on the above example, let's assume that a pass now needs to use the exact same pipeline and shaders with a different texture. Creating a whole separate QRhiGraphicsPipeline just for this would be an overkill. This is why QRhiCommandBuffer::setShaderResources() allows specifying a srb argument. As long as the layouts (so the number of bindings and the binding points) match between two QRhiShaderResourceBindings, they can both be used with the same pipeline, assuming the pipeline was built with one of them in the first place.

Creating and then using a new srb2 that is very similar to srb with the exception of referencing another texture could be implemented like the following:

  srb2 = rhi->newShaderResourceBindings();
  QVector<QRhiShaderResourceBinding> bindings = srb->bindings();
  bindings[1] = QRhiShaderResourceBinding::sampledTexture(1, QRhiShaderResourceBinding::FragmentStage, anotherTexture, sampler);
  srb2->setBindings(bindings);
  srb2->build();
  ...
  cb->setGraphicsPipeline(ps);
  cb->setShaderResources(srb2); // binds srb2