shaderc selects colliding slots for uniforms and globals.

[mcourteaux]

Describe the bug
Have a shader like this:

uniform vec4 u_some_param;
mat3 some_matrix = mtxFromRows(vec3(1), vec3(2), vec3(3));

And compile with shaderc to spirv. Then in the vulkan backend you should see non-unique register slots when compiled with trace-level logging when the shader gets loaded.

Note that the actual some_matrix global is not even marked as uniform.

This bug was revealed when https://github.com/bkaradzic/bgfx/pull/3536/changes landed, and I had to change mtxFromRows3 to mtxFromRows. This new approach is however not a constant expression anymore, so I had to drop the const qualifier from the global declaration.

Screenshots

In screenshot see how u_crop is at offset 48, and how the selected line m_XYZ_to_ProPhoto is at offset 48.

I'm not sure if non-const globals being treated as uniforms is an intentional way of getting constant data into the shader.

[mcourteaux]

Besides the bug in shaderc, I propose reinstating these macros:

#if BGFX_SHADER_MATRIX_COLUMN_MAJOR
#define mtxFromRows3(_0, _1, _2)     transpose(mat3(_0, _1, _2) )
#define mtxFromRows4(_0, _1, _2, _3) transpose(mat4(_0, _1, _2, _3) )
#define mtxFromCols3(_0, _1, _2)               mat3(_0, _1, _2)
#define mtxFromCols4(_0, _1, _2, _3)           mat4(_0, _1, _2, _3)
#else
#define mtxFromRows3(_0, _1, _2)               mat3(_0, _1, _2)
#define mtxFromRows4(_0, _1, _2, _3)           mat4(_0, _1, _2, _3)
#define mtxFromCols3(_0, _1, _2)     transpose(mat3(_0, _1, _2) )
#define mtxFromCols4(_0, _1, _2, _3) transpose(mat4(_0, _1, _2, _3) )
#endif

[bkaradzic]

Probably better to call it mat[3/4]From[Rows/Column].

[mcourteaux]

Okay, shaderc treats them both as uniforms, but coming from different UniformBlocks, UniformBlock and $Global:

shaderc_spirv.cpp(709): BX Uniform 'u_debug_bits' at offset 480 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'm_XYZ_to_OklabCone' at offset 96 with regcount 3, in block 1 '$Global'
shaderc_spirv.cpp(709): BX Uniform 'm_OklabConeCbrt_to_Oklab' at offset 144 with regcount 3, in block 1 '$Global'
shaderc_spirv.cpp(709): BX Uniform 'm_Oklab_to_OklabConeCbrt' at offset 240 with regcount 3, in block 1 '$Global'
shaderc_spirv.cpp(709): BX Uniform 'm_OklabCone_to_XYZ' at offset 192 with regcount 3, in block 1 '$Global'
shaderc_spirv.cpp(709): BX Uniform 'u_bilateral_grid_sample_correction_factor' at offset 496 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_exposure_EV' at offset 80 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_contrast' at offset 112 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_hf' at offset 16 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_LMS_grad_shadows' at offset 512 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_LMS_grad_midtones' at offset 528 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_LMS_grad_highlights' at offset 544 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_hlrec_params' at offset 560 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_RAW_wb_coef' at offset 416 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_hlrec_color' at offset 576 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_source_to_XYZ' at offset 304 with regcount 3, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_XYZ_to_screen' at offset 352 with regcount 3, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_RAW_lum_coef' at offset 400 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_effect_strengths_0' at offset 144 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_effects_0' at offset 128 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_viewRect' at offset 0 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_crop' at offset 48 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_crop_info' at offset 64 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_input_metadata' at offset 32 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_sharpening' at offset 160 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_sharpen_texture_rect' at offset 176 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_denoise_texture_rect' at offset 192 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_XYZ_to_LMS' at offset 208 with regcount 3, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_LMS_gains' at offset 96 with regcount 1, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'u_LMS_to_XYZ' at offset 256 with regcount 3, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'm_XYZ_to_ProPhoto' at offset 48 with regcount 3, in block 1 '$Global'
shaderc_spirv.cpp(709): BX Uniform 'u_color_effect' at offset 432 with regcount 3, in block 0 'UniformBlock'
shaderc_spirv.cpp(709): BX Uniform 'm_ProPhoto_to_XYZ' at offset 0 with regcount 3, in block 1 '$Global'

uint8_t bi = program->getUniformBlockIndex(ii);
BX_TRACE("Uniform '%s' at offset %d with regcount %d, in block %d '%s'",
		un.name.c_str(),
		un.regIndex,
		un.regCount,
		bi,
		program->getUniformBlockName(bi)
		);

So, not sure where the data of the globals sit.
Are they in the shader baked, or is it the Vulkan backends task to provide those?

[bkaradzic]

These m_ are constants and u_ are uniforms?

[mcourteaux]

These m_ are constants and u_ are uniforms?

Yes, that was my internal convention for my shaders.