GL_IMAGE_SAMPLER_NAME_NOT_FOUND_IN_SHADER: image-sampler name not found in shader

[AlexanderArvidsson]

When using multiple samplers in a fragment shader, the program runs fine, but I get errors in my terminal:

[sg][error][id:8] c/sokol_gfx.h:8809:0: 
	GL_IMAGE_SAMPLER_NAME_NOT_FOUND_IN_SHADER: image-sampler name not found in shader (gl)

[sg][info][id:8] c/sokol_gfx.h:8810:0: 
	tex_position_smp_position

[sg][error][id:8] c/sokol_gfx.h:8809:0: 
	GL_IMAGE_SAMPLER_NAME_NOT_FOUND_IN_SHADER: image-sampler name not found in shader (gl)

[sg][info][id:8] c/sokol_gfx.h:8810:0: 
	tex_normal_smp_normal

[sg][error][id:8] c/sokol_gfx.h:8809:0: 
	GL_IMAGE_SAMPLER_NAME_NOT_FOUND_IN_SHADER: image-sampler name not found in shader (gl)

[sg][info][id:8] c/sokol_gfx.h:8810:0: 
	tex_depth_smp_depth

Here's my uniforms in my shader (for deferred rendering in a fullscreen quad):

layout(binding=0) uniform texture2D tex_color;
layout(binding=0) uniform sampler smp_color;

layout(binding=1) uniform texture2D tex_position;
layout(binding=1) uniform sampler smp_position;

layout(binding=2) uniform texture2D tex_normal;
layout(binding=2) uniform sampler smp_normal;

@image_sample_type tex_depth unfilterable_float
@sampler_type smp_depth nonfiltering
layout(binding=3) uniform texture2D tex_depth;
layout(binding=3) uniform sampler smp_depth;

Here's my shader pipeline (in Odin):

	g_mem.fullscreen.shader = sg.make_shader(fullscreen_shader_desc(sg.query_backend()))
	g_mem.fullscreen.pip = sg.make_pipeline(
		{
			shader = g_mem.fullscreen.shader,
			layout = {
				attrs = {
					ATTR_fullscreen_position = {format = .FLOAT4},
					ATTR_fullscreen_texcoord0 = {format = .FLOAT2},
				},
			},
			index_type = .UINT16,
			cull_mode = .BACK,
			depth = {compare = .LESS_EQUAL, write_enabled = true},
		},
	)

Here's the generated code form shdc (Odin):

    /*
    layout(binding = 16) uniform sampler2D tex_color_smp_color;
    layout(binding = 17) uniform sampler2D tex_position_smp_position;
    layout(binding = 18) uniform sampler2D tex_normal_smp_normal;
    layout(binding = 19) uniform sampler2D tex_depth_smp_depth;
    */

    case .GLCORE:
        desc.vertex_func.source = transmute(cstring)&vs_source_glsl430
        desc.vertex_func.entry = "main"
        desc.fragment_func.source = transmute(cstring)&fs_source_glsl430
        desc.fragment_func.entry = "main"
        desc.attrs[0].glsl_name = "position"
        desc.attrs[1].glsl_name = "texcoord0"
        desc.uniform_blocks[0].stage = .VERTEX
        desc.uniform_blocks[0].layout = .STD140
        desc.uniform_blocks[0].size = 80
        desc.uniform_blocks[0].glsl_uniforms[0].type = .FLOAT4
        desc.uniform_blocks[0].glsl_uniforms[0].array_count = 5
        desc.uniform_blocks[0].glsl_uniforms[0].glsl_name = "vs_fullscreen_params"
        desc.uniform_blocks[1].stage = .FRAGMENT
        desc.uniform_blocks[1].layout = .STD140
        desc.uniform_blocks[1].size = 16
        desc.uniform_blocks[1].glsl_uniforms[0].type = .FLOAT4
        desc.uniform_blocks[1].glsl_uniforms[0].array_count = 1
        desc.uniform_blocks[1].glsl_uniforms[0].glsl_name = "fs_fullscreen_params"
        desc.images[0].stage = .FRAGMENT
        desc.images[0].multisampled = false
        desc.images[0].image_type = ._2D
        desc.images[0].sample_type = .FLOAT
        desc.images[1].stage = .FRAGMENT
        desc.images[1].multisampled = false
        desc.images[1].image_type = ._2D
        desc.images[1].sample_type = .FLOAT
        desc.images[2].stage = .FRAGMENT
        desc.images[2].multisampled = false
        desc.images[2].image_type = ._2D
        desc.images[2].sample_type = .FLOAT
        desc.images[3].stage = .FRAGMENT
        desc.images[3].multisampled = false
        desc.images[3].image_type = ._2D
        desc.images[3].sample_type = .UNFILTERABLE_FLOAT
        desc.samplers[0].stage = .FRAGMENT
        desc.samplers[0].sampler_type = .FILTERING
        desc.samplers[1].stage = .FRAGMENT
        desc.samplers[1].sampler_type = .FILTERING
        desc.samplers[2].stage = .FRAGMENT
        desc.samplers[2].sampler_type = .FILTERING
        desc.samplers[3].stage = .FRAGMENT
        desc.samplers[3].sampler_type = .NONFILTERING
        desc.image_sampler_pairs[0].stage = .FRAGMENT
        desc.image_sampler_pairs[0].image_slot = 0
        desc.image_sampler_pairs[0].sampler_slot = 0
        desc.image_sampler_pairs[0].glsl_name = "tex_color_smp_color"
        desc.image_sampler_pairs[1].stage = .FRAGMENT
        desc.image_sampler_pairs[1].image_slot = 1
        desc.image_sampler_pairs[1].sampler_slot = 1
        desc.image_sampler_pairs[1].glsl_name = "tex_position_smp_position"
        desc.image_sampler_pairs[2].stage = .FRAGMENT
        desc.image_sampler_pairs[2].image_slot = 2
        desc.image_sampler_pairs[2].sampler_slot = 2
        desc.image_sampler_pairs[2].glsl_name = "tex_normal_smp_normal"
        desc.image_sampler_pairs[3].stage = .FRAGMENT
        desc.image_sampler_pairs[3].image_slot = 3
        desc.image_sampler_pairs[3].sampler_slot = 3
        desc.image_sampler_pairs[3].glsl_name = "tex_depth_smp_depth"

This error only shows up from the _sg_gl_create_shader function in the form of an error, but the program runs fine after that and I can read from the texture using the samplers correctly.

No error shows up on Metal on my MacOS.

I can't find many examples with multiple samplers so I could be doing something wrong here, please let me know!

[floooh]

Hmm, that means the glGetUniformLocation() call here returned -1:

https://github.com/floooh/sokol/blob/c1cc713a48669fb78c8fadc1a3cb9dd6c3bb97d3/sokol_gfx.h#L8803C24-L8811

GLSL compilers like to remove resource bindings that are not actually used in the shader code. Can you paste the GLSL code passed into sokol-gfx? It's in the sokol-shdc output file as comment above the 'shader code arrays', e.g.:

https://github.com/floooh/sokol-odin/blob/2c47c1fdcc6f86fad1f2b3e03559e35bb50df6cc/examples/cube/shader.odin#L70-L81

I'm actually not sure if this situation should be logged as an error by sokol-gfx, it's at best a warning. It shouldn't be completely silent though, because sometimes it is actually something that needs to be fixed.

[AlexanderArvidsson]

You're absolutely right! Since I wasn't done with my shader, I found that I could force the compiler to not omit my variables if I set my frag_color out attribute multiple times:

       frag_color = vec4(vec3(depth), 1);
       frag_color = position;
       frag_color = vec4(normal, 1);
       frag_color = color;

That way, I didn't get compile errors. But that must have still lead it to be excluded by GLSL, but not MSL. Understandable, it was a lazy hack to get things moving without having to comment in and out every other change.
Now that I've gotten a lot more work done on my shader and I'm actually using my samplers, the errors are gone.

May I suggest adding a hint about this in the error message? Since the program technically works like it should even when this error is logged, I think it should be a warning with a hint what could be wrong (i.e. unused sampler)!

[floooh]

May I suggest adding a hint about this in the error message?

Yeah, I'll keep the issue open until I get around to improving the error message.