Error when sampling with seperate sampler and texture

Vulkan
1

I am failing to properly use a separate sampler and texture in my glsl code. glslangValidator refuses to compile my code with this error:
ERROR: shader/simple_push_const.frag:21: 'sampler/image' : cannot construct this type

The only source I know of which demonstrates proper usage is GL_KHR_vulkan_glsl, and here is my interpretation:


#version 450
#extension GL_KHR_vulkan_glsl : enable    // tried this, not sure if required, get no error from this line

layout( set = 0, binding = 3 ) uniform texture2D my_tex;      // VK_DESCRIPTOR_TYPE_SAMPLED_IMAGE
layout( set = 0, binding = 4 ) uniform sampler   my_sampler;  // VK_DESCRIPTOR_TYPE_SAMPLER

layout( location = 0 ) in  vec3 vsNormal;
layout( location = 1 ) in  vec2 vsTexCoord;
layout( location = 0 ) out vec4 fsColor;

void main() {
    // ...
    vec4 rgba = texture( texture2D( sampler2D( my_tex, my_sampler )), vsTexCoord );    // line 21
    // ...
}

What am I missing?

2

Why are you constructing a texture2D from a sampler2D? You simply need to combine your existing texture2D with your sampler, which you did with sampler2D(my_tex, my_sampler). That’s the parameter you pass to texture.

3

#extension GL_KHR_vulkan_glsl : enable // tried this, not sure if required, get no error from this line

KHR_vulkan_glsl spec:

This extension is not enabled with a #extension as other extensions are.
[…]
Instead, use of this extension is an effect of using a GLSL front-end in a
mode that has it generate SPIR-V for Vulkan.

4

Because of the example in the extension description:

    Constructors can then be used to combine a sampler and a texture at the
    point of making a texture lookup call:

        texture2D(sampler2D(t, s), ...);

Note: ```

texture2D

The following features are removed:
    * ...
    * the already deprecated texturing functions (e.g., texture2D())


However, you are right,

vec4 rgba = texture( sampler2D( my_tex, my_sampler ), vsTexCoord );

 works, thanks.

Btw, I wonder why such an example is not in the spec. Without "accidentally" reading GL_KHR_vulkan_glsl extension I would not know how to use it at all. I'll create an issue.
5

Ah, it’s an error in the specification then.

6

One you post this issue on Github, would you be able to post back here with the issue #id. Thanks.

7

Issue #466.

8

Thanks, missed that one.