more wip sokol-gfx bindings cleanup support

src/shdc/reflection.cc

@@ -74,8 +74,9 @@ static ErrMsg validate_linking(const Input& inp, const Program& prog, const Prog
 Reflection Reflection::build(const Args& args, const Input& inp, const std::array<Spirvcross,Slang::Num>& spirvcross_array) {
     Reflection res;
 
-    // for each program, just pick the reflection info from the first compiled slang
-    // FIXME: we should check whether the reflection info of all compiled slangs actually matches
+    // for each program, just pick the reflection info from the first compiled slang,
+    // the reflection info is the same for each Slang because it has been generated
+    // with the special Slang::REFLECTION, not the actual slang.
     for (const auto& item: inp.programs) {
         const Program& prog = item.second;
         int vs_snippet_index = inp.snippet_map.at(prog.vs_name);

src/shdc/reflection.h

@@ -24,6 +24,9 @@ struct Reflection {
     static Reflection build(const Args& args, const Input& inp, const std::array<Spirvcross,Slang::Num>& spirvcross);
     // parse per-snippet reflection info for a compiled shader source
     static StageReflection parse_snippet_reflection(const spirv_cross::Compiler& compiler, const Snippet& snippet, ErrMsg& out_error);
+
+FIXME: add a static helper function which returns binding base by slang, stage and resource type
+
     // print a debug dump to stderr
     void dump_debug(ErrMsg::Format err_fmt) const;
 

src/shdc/spirvcross.cc

@@ -31,8 +31,14 @@ const SpirvcrossSource* Spirvcross::find_source_by_snippet_index(int snippet_ind
 }
 
 static void fix_bind_slots(Compiler& compiler, Snippet::Type type, Slang::Enum slang) {
+    // WGSL bindslot fixup is handled elsewhere
+    // Also note that this function can be called with the special Slang::REFLECTION
+    // which guarantees zero-based bindings for each resource type
+    assert(!Slang::is_wgsl(slang));
     ShaderResources shader_resources = compiler.get_shader_resources();
 
+FIXME: use the new Reflection::binding_base() helper function
+
     // uniform buffers
     {
         uint32_t binding = 0;
@@ -43,11 +49,17 @@ static void fix_bind_slots(Compiler& compiler, Snippet::Type type, Slang::Enum s
     }
 
     // combined image samplers
-    // FIXME: technically this is wrong since image-samplers have a common
-    // bind space across shader stages, but since the binding happens via
-    // name lookup the DecorationBinding is actually ignored.
     {
-        uint32_t binding = 0;
+        uint32_t binding;
+        if (Slang::is_glsl(slang)) {
+            // GLSL has a common bind space across shader stages, so make sure
+            // that bindings can't collide.
+            // NOTE though that currently that binding isn't used by sokol-gfx
+            // because image-samplers use name-lookup
+            binding = Snippet::is_vs(type) ? 0 : ImageSampler::Num;
+        } else {
+            binding = 0;
+        }
         for (const Resource& res: shader_resources.sampled_images) {
             compiler.set_decoration(res.id, spv::DecorationDescriptorSet, 0);
             compiler.set_decoration(res.id, spv::DecorationBinding, binding++);
@@ -76,17 +88,17 @@ static void fix_bind_slots(Compiler& compiler, Snippet::Type type, Slang::Enum s
     {
         uint32_t binding;
         if (Slang::is_msl(slang)) {
-            // in Metal, on the vertex stage, storage buffers are bound after uniform- and vertex-buffers,
-            // and on the fragment stage, after the uniform buffers
-            binding = Snippet::is_vs(type) ? 12 : 4;
+            // in Metal, all buffers have a common bind space per stage,
+            // bind storage buffers after uniform buffers
+            binding = UniformBlock::Num;
         } else if (Slang::is_hlsl(slang)) {
-            // in D3D11, storage buffers share bind slots with textures, put textures into
-            // the first 16 slots, and storage buffers starting at slot 16
-            binding = 16;
+            // in D3D11, textures and storage buffers have a common bind space
+            // per stage, bind storage buffers after textures
+            binding = Image::Num;
         } else if (Slang::is_glsl(slang)) {
             // in GL, the shader stages share a common bind space, need to offset
             // fragment bindings
-            binding = Snippet::is_vs(type) ? 0 : 8;
+            binding = Snippet::is_vs(type) ? 0 : StorageBuffer::Num;
         } else {
             binding = 0;
         }
@@ -103,25 +115,30 @@ static void fix_bind_slots(Compiler& compiler, Snippet::Type type, Slang::Enum s
 static void wgsl_patch_bind_slots(Compiler& compiler, Snippet::Type type, std::vector<uint32_t>& inout_bytecode) {
     ShaderResources shader_resources = compiler.get_shader_resources();
 
-    // WGPU bindgroups and binding offsets are hardwired:
+    // even though sokol-gfx is flexible now, still use specific
+    // bind slot ranges here:
+    //
     //  - bindgroup 0 for uniform buffer bindings
     //      - vertex stage bindings start at 0
-    //      - fragment stage bindings start at 4
+    //      - fragment stage bindings start at UniformBlock::Num (8)
     //  - bindgroup 1 for all images, samplers and storage buffers
     //      - vertex stage image bindings start at 0
-    //      - vertex stage sampler bindings start at 16
-    //      - vertex stage storage buffer bindings start at 32
-    //      - fragment stage image bindings start at 48
-    //      - fragment stage sampler bindings start at 64
-    //      - fragment stage storage buffer bindings start at 80
+    //      - vertex stage sampler bindings start at Image::Num (16)
+    //      - vertex stage storage buffer bindings start at Image::Num + Sampler::Num (32)
+    //      - fragment stage image bindings start at 64
+    //      - fragment stage sampler bindings start at 64 + Image::Num (80)
+    //      - fragment stage storage buffer bindings start at 64 + Image::Num + Sampler::Num (96)
+
+FIXME: use the new Reflection::binding_base() helper function instead
+
     const uint32_t wgsl_vs_ub_bind_offset = 0;
-    const uint32_t wgsl_fs_ub_bind_offset = 4;
+    const uint32_t wgsl_fs_ub_bind_offset = UniformBlock::Num;
     const uint32_t wgsl_vs_img_bind_offset = 0;
-    const uint32_t wgsl_vs_smp_bind_offset = 16;
-    const uint32_t wgsl_vs_sbuf_bind_offset = 32;
-    const uint32_t wgsl_fs_img_bind_offset = 48;
-    const uint32_t wgsl_fs_smp_bind_offset = 64;
-    const uint32_t wgsl_fs_sbuf_bind_offset = 80;
+    const uint32_t wgsl_vs_smp_bind_offset = Image::Num;
+    const uint32_t wgsl_vs_sbuf_bind_offset = Image::Num + Sampler::Num;
+    const uint32_t wgsl_fs_img_bind_offset = 64;
+    const uint32_t wgsl_fs_smp_bind_offset = 64 + Image::Num;
+    const uint32_t wgsl_fs_sbuf_bind_offset = 64 + Image::Num + Sampler::Num;
 
     const uint32_t ub_bindgroup = 0;
     const uint32_t res_bindgroup = 1;
@@ -130,7 +147,6 @@ static void wgsl_patch_bind_slots(Compiler& compiler, Snippet::Type type, std::v
     uint32_t cur_sampler_binding = Snippet::is_vs(type) ? wgsl_vs_smp_bind_offset : wgsl_fs_smp_bind_offset;
     uint32_t cur_sbuf_binding = Snippet::is_vs(type) ? wgsl_vs_sbuf_bind_offset : wgsl_fs_sbuf_bind_offset;
 
-
     // uniform buffers
     {
         for (const Resource& res: shader_resources.uniform_buffers) {
@@ -315,6 +331,9 @@ static StageReflection parse_reflection(const std::vector<uint32_t>& bytecode, c
     compiler.set_common_options(options);
     flatten_uniform_blocks(compiler);
     to_combined_image_samplers(compiler);
+    // passing Slang::REFLECTION here makes sure that the bind slots
+    // are zero-based per stage and resource type (otherwise 3D API
+    // specific bind slot allocations would apply)
     fix_bind_slots(compiler, snippet.type, Slang::REFLECTION);
     // NOTE: we need to compile here, otherwise the reflection won't be
     // able to detect depth-textures and comparison-samplers!

src/shdc/types/reflection/image.h

@@ -8,7 +8,7 @@
 namespace shdc::refl {
 
 struct Image {
-    static const int Num = 12;        // must be identical with SG_MAX_SHADERSTAGE_IMAGES
+    static const int Num = 16; // must be identical with SG_MAX_IMAGE_BINDSLOTS
     ShaderStage::Enum stage = ShaderStage::Invalid;
     int slot = -1;
     std::string name;

src/shdc/types/reflection/image_sampler.h

@@ -7,7 +7,7 @@ namespace shdc::refl {
 
 // special combined-image-samplers for GLSL output with GL semantics
 struct ImageSampler {
-    static const int Num = 12;      // must be identical with SG_MAX_SHADERSTAGE_IMAGES
+    static const int Num = 16; // must be identical with SG_MAX_IMAGE_SAMPLER_PAIRS
     ShaderStage::Enum stage = ShaderStage::Invalid;
     int slot = -1;
     std::string name;

src/shdc/types/reflection/sampler.h

@@ -7,7 +7,7 @@
 namespace shdc::refl {
 
 struct Sampler {
-    static const int Num = 12;      // must be identical with SG_MAX_SHADERSTAGE_SAMPLERS
+    static const int Num = 16; // must be identical with SG_MAX_SAMPLER_BINDSLOTS
     ShaderStage::Enum stage = ShaderStage::Invalid;
     int slot = -1;
     std::string name;

src/shdc/types/reflection/storage_buffer.h

@@ -7,7 +7,7 @@
 namespace shdc::refl {
 
 struct StorageBuffer {
-    static const int Num = 8;   // must be identical with SG_MAX_SHADERSTAGE_STORAGE_BUFFERS
+    static const int Num = 8; // must be identical with SG_MAX_STORAGEBUFFER_BINDSLOTS
     ShaderStage::Enum stage = ShaderStage::Invalid;
     int slot = -1;
     std::string inst_name;

src/shdc/types/reflection/uniform_block.h

@@ -8,7 +8,7 @@
 namespace shdc::refl {
 
 struct UniformBlock {
-    static const int Num = 4;     // must be identical with SG_MAX_SHADERSTAGE_UBS
+    static const int Num = 8; // must be identical with SG_MAX_UNIFORMBLOCK_BINDSLOTS
     ShaderStage::Enum stage = ShaderStage::Invalid;
     int slot = -1;
     std::string inst_name;