UBO bindings to different stages

Vulkan
1

Hi! I am slowly moving from triangle example, and I’ve successfully binded uniform buffer object to vertex shader. Now I am unable to make 2 bindings - 1 for vertex shader, and 1 for fragment - I get incorrect even vertex binding.
Everything compiles and runs, but does not work.

So, I am trying to expand binding to vertex shader (works finto bindinf to vertex and fragment shader

  1. Changing binding count
    VkPipelineVertexInputStateCreateInfo::vertexAttributeDescriptionCount 1 => 2

  2. Adding vertex input binding description
    demo->vertices.vi_bindings[0].binding = VERTEX_BUFFER_BIND_ID;
    demo->vertices.vi_bindings[0].stride = sizeof(vb[0]);
    demo->vertices.vi_bindings[0].inputRate = VK_VERTEX_INPUT_RATE_VERTEX;

adding =>

demo->vertices.vi_bindings[1].binding = 0;
demo->vertices.vi_bindings[1].stride = sizeof(vb[0]);
demo->vertices.vi_bindings[1].inputRate = VK_VERTEX_INPUT_RATE_VERTEX;

  1. Adding device-mapped buffer with helper (simply has set(…) method with embedded mapping/unmapping)

context->uboVert = new vk_buffer_proxy<vertex_uniform_t>(context->device);

adding =>

context->uboFrag = new vk_buffer_proxy<fragment_uniform_t>(context->device);

  1. Adding one more VkWriteDescriptorSet element

writes[0].sType = VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET;
writes[0].dstSet = context->desc_set;
writes[0].descriptorCount = 1;
writes[0].descriptorType = VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
writes[0].pBufferInfo = &context->uboVert->descriptor;
writes[0].dstBinding = 0;

adding =>

writes[1].sType = VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET;
writes[1].dstSet = context->desc_set;
writes[1].descriptorCount = 1;
writes[1].descriptorType = VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
writes[1].pBufferInfo = &context->uboFrag->descriptor;
writes[1].dstBinding = 0;

and calling vkUpdateDescriptorSets with 2

  1. Now shaders have

vert:

layout(set = 0, binding = 0) uniform MainBlock
{
mat4 mvMatrix;
float green_uni;
float sc;
} ubo;

frag:

layout(set = 0, binding = 0) uniform MainBlock
{
vec3 color;
} ubo;

Before each frame I set values of both buffer mappings, and even vertex ubo is not correct on the shader side. Please tell me what’s wrong, I am really new to Vulkan and after Opengl 1.2-2 it seems too different.
And after these changes vertex ubo is not

2

Changing binding count

The number of vertex shader attributes is irrelevant to the number of uniform buffers you use. So I have no idea what you’re trying to do with that. The same goes for your vertex input changes.

UBOs are descriptors, not attributes.

Adding one more VkWriteDescriptorSet element

… Did you change your descriptor set layout to include another UBO?

vert:

layout(set = 0, binding = 0) uniform MainBlock
{
mat4 mvMatrix;
float green_uni;
float sc;
} ubo;

frag:

layout(set = 0, binding = 0) uniform MainBlock
{
vec3 color;
} ubo;

You gave them both the same descriptor binding index. That’s not going to work, since they store different data and come from different buffer regions.

3

So, firstly should I change shaders code to:

layout(set = 0, binding = 0) uniform MainBlock
{
mat4 mvMatrix;
float green_uni;
float sc;
} ubo;

frag:

layout(set = 0, binding = 1) uniform MainBlock
{
vec3 color;
} ubo

?

4

  1. OK, I changed shader so now vertex has 0-binding, and fragment 1-binding.

  2. Next, I removed second VkVertexInputBindingDescription. (but it is not attribute binding, it is VkVertexInputBindingDescription, or it is the corresponding entity?)

  3. In the first post I forgot to add, that I also added an element to descriptor set layout:

layout_bindings[0].descriptorType = VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
layout_bindings[0].descriptorCount = 1;
layout_bindings[0].stageFlags = VK_SHADER_STAGE_VERTEX_BIT;
layout_bindings[0].pImmutableSamplers = NULL;

added =>

layout_bindings[1].descriptorType = VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
layout_bindings[1].descriptorCount = 1;
layout_bindings[1].stageFlags = VK_SHADER_STAGE_FRAGMENT_BIT;
layout_bindings[1].pImmutableSamplers = NULL;

  1. changed
    layout(set = 0, binding = 1) uniform MainBlock
    {
    vec3 color;
    } ubo

=>

layout(set = 0, binding = 1) uniform MainBlock
{
vec4 color;
} ubo

due to suspiction of not using strict 4-byte alignment

  1. Now the last line of updating descriptor sets crashes:

VkWriteDescriptorSet writes[2];
memset(writes, 0, sizeof(writes));

writes[0].sType = VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET;
writes[0].dstSet = context-&gt;desc_set;
writes[0].descriptorCount = 1;
writes[0].descriptorType = VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
writes[0].pBufferInfo = &context-&gt;uboVert-&gt;descriptor;
writes[0].dstBinding = 0;

writes[1].sType = VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET;
writes[1].dstSet = context-&gt;desc_set;
writes[1].descriptorCount = 1;
writes[1].descriptorType = VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
writes[1].pBufferInfo = &context-&gt;uboFrag-&gt;descriptor;
writes[1].dstBinding = 1;

vkUpdateDescriptorSets(context-&gt;device, 2, writes, 0, NULL);
5

Ha! Finally found the problem, the following lines were missing:

VkDescriptorSetLayoutBinding layout_bindings[2];

layout_bindings[0].binding = 0;
layout_bindings[1].binding = 1;

Now it works!