[Feat, Fix, Test] (MG_Util, MG_Backend/DirectGLES, MG_IntegrationTest): bake the bound image format into the ESSL a format-less image declaration needs

MobileGL/MG_Backend/DirectGLES/DirectGLES.cpp

@@ -2195,7 +2195,15 @@ namespace MobileGL::MG_Backend::DirectGLES {
                 twin->GetUnormFallbackClampOutputMask() != g_unormFallbackClampOutputMask ||
                 twin->GetFragColorBroadcastCount() != g_fragColorBroadcastCount ||
                 twin->GetShaderStorageBlockBindingSignature() !=
-                    ComputeShaderStorageBlockBindingSignature(*currentProgram)) {
+                    ComputeShaderStorageBlockBindingSignature(*currentProgram) ||
+                // A fourth of the same shape, and the reason glBindImageTexture itself does
+                // nothing: GLSL ES demands a format layout qualifier on an image where desktop
+                // GLSL lets a writeonly declaration omit one, so a format-less declaration is
+                // compiled against the format the application BOUND, and a rebind to a
+                // different one makes what was built wrong. Asked of the twin because only it
+                // knows which units its own images address - and answered by an empty-vector
+                // test for every program that declares its formats, which is nearly all of them.
+                !twin->ImageUnitFormatsStillMatch()) {
                 twin->SyncToBackend(currentProgram);
             }
             g_currentDrawFrontendProgram = currentProgram.get();

MobileGL/MG_Backend/DirectGLES/Managers.cpp

@@ -4497,6 +4497,161 @@ namespace MobileGL::MG_Backend::DirectGLES {
             return signature;
         }
 
+        namespace {
+            // The GL internal format bound to an image unit right now. GL_NONE for a unit
+            // outside the frontend's array, which cannot be addressed at all.
+            Uint BoundImageUnitFormat(Int unit) {
+                if (unit < 0 || unit >= MG_State::GLState::TextureState::MAX_TEXTURE_IMAGE_UNITS) return 0;
+                return static_cast<Uint>(MG_State::pGLContext->GetImageTextureBinding(unit).Format);
+            }
+
+            // Combines one (unit, format) pair into a running digest. Commutative, so the order
+            // the uniforms are walked in cannot change the answer, and mixed rather than summed
+            // so a unit and a format cannot trade places between two pairs and cancel out.
+            Uint64 MixImageUnitFormat(Uint64 signature, Int unit, Uint format) {
+                Uint64 entry = static_cast<Uint64>(static_cast<Uint32>(unit)) + 0x9e3779b97f4a7c15ull;
+                entry ^= static_cast<Uint64>(format) + 0xbf58476d1ce4e5b9ull + (entry << 6) + (entry >> 2);
+                return signature + entry;
+            }
+
+            // Reflection names an array uniform after its first element ("g_image[0]") at every
+            // location it spans; SPIR-V names the variable once, without the subscript. This is
+            // the name both sides agree on.
+            String ImageUniformBaseName(const String& reflectionName) {
+                if (reflectionName.size() >= 3 && reflectionName.compare(reflectionName.size() - 3, 3, "[0]") == 0) {
+                    return reflectionName.substr(0, reflectionName.size() - 3);
+                }
+                return reflectionName;
+            }
+
+            // Whether a glslang layout format is one GLSL ES has in core; the rest reach ES only
+            // through GL_NV_image_formats. Asked of DECLARED formats, which this backend passes
+            // through untouched - the emitted ESSL still has to be legal for the driver.
+            Bool IsCoreEsslLayoutFormat(glslang::TLayoutFormat format) {
+                switch (format) {
+                case glslang::ElfRgba32f:
+                case glslang::ElfRgba16f:
+                case glslang::ElfR32f:
+                case glslang::ElfRgba8:
+                case glslang::ElfRgba8Snorm:
+                case glslang::ElfRgba32i:
+                case glslang::ElfRgba16i:
+                case glslang::ElfRgba8i:
+                case glslang::ElfR32i:
+                case glslang::ElfRgba32ui:
+                case glslang::ElfRgba16ui:
+                case glslang::ElfRgba8ui:
+                case glslang::ElfR32ui:
+                    return true;
+                default:
+                    return false;
+                }
+            }
+        } // namespace
+
+        // What the format bake needs from the frontend, collected in one walk of the uniform
+        // reflection: which image uniforms declared NO format (the only ones a bake may touch -
+        // a declared format is authoritative and stays), what the units they address currently
+        // hold, and whether any format in play - declared or baked - is outside the ES core set.
+        ImageFormatBakeInputs CollectImageFormatBakeInputs(
+            const MG_State::GLState::ProgramObject& stateProgramObject) {
+            ImageFormatBakeInputs inputs;
+            const Uint maxUniformLoc = stateProgramObject.GetMaxUniformLocation();
+            for (Uint loc = 0; loc <= maxUniformLoc; ++loc) {
+                const auto& name = stateProgramObject.GetUniformName(loc);
+                if (name.empty()) continue;
+                if (!IsImageUniformType(stateProgramObject.GetUniformType(loc))) continue;
+                const glslang::TType* type = stateProgramObject.GetUniformTType(loc);
+                if (type == nullptr) continue;
+                if (type->getQualifier().hasFormat()) {
+                    // Declared, and therefore left exactly as written - but a non-core spelling
+                    // still needs the extension directive to survive the ES compiler.
+                    if (!IsCoreEsslLayoutFormat(type->getQualifier().getFormat())) {
+                        inputs.needsExtendedImageFormats = true;
+                    }
+                    continue;
+                }
+                const Int unit = stateProgramObject.GetUniformSamplerOrImageUnitIndex(loc);
+                if (unit < 0 || unit >= MG_State::GLState::TextureState::MAX_TEXTURE_IMAGE_UNITS) continue;
+                const Uint boundFormat = BoundImageUnitFormat(unit);
+
+                // Every format-less uniform contributes to the rebuild key, including one whose
+                // unit holds nothing yet: an image bound for the first time AFTER the link has
+                // to move the key, or the program built against "nothing bound" would never be
+                // rebuilt against the real format.
+                inputs.units.push_back(unit);
+                inputs.signature = MixImageUnitFormat(inputs.signature, unit, boundFormat);
+
+                if (boundFormat == 0) continue;
+                if (!MG_Util::ShaderTranspiler::ShaderCompiler::GLInternalFormatIsCoreEsslImageFormat(boundFormat)) {
+                    // Outside the GLSL ES core set, so the emitted ESSL only compiles with
+                    // GL_NV_image_formats. Without the extension there is no legal spelling at
+                    // all, and baking one would trade a "no format qualifier" compile error for
+                    // an "unsupported format" one - so the image is left format-less. Its unit
+                    // stays in the key, so a rebind to a core format still rebuilds and works.
+                    if (!g_GLESCapabilities.SupportsExtendedImageFormats) {
+                        MGLOG_D("Image uniform '%s' has no declared format and its unit %d holds 0x%x, which GLSL ES "
+                                "core cannot spell and this driver has no GL_NV_image_formats for.",
+                                name.c_str(), unit, boundFormat);
+                        continue;
+                    }
+                    inputs.needsExtendedImageFormats = true;
+                }
+                const String baseName = ImageUniformBaseName(name);
+                const auto existing = inputs.glFormatByUniformName.find(baseName);
+                if (existing == inputs.glFormatByUniformName.end()) {
+                    inputs.glFormatByUniformName.emplace(baseName, boundFormat);
+                } else if (existing->second != boundFormat) {
+                    // An ARRAY whose elements were pointed at units holding different formats.
+                    // One declaration carries one qualifier, so there is no spelling for it, and
+                    // the uniform is left format-less rather than given a format that is wrong
+                    // for all but one element. Marked in place with GL_NONE and swept below -
+                    // never by erasing here, because the entry is reached again by the array's
+                    // remaining elements and a flat hash map must not be mutated structurally
+                    // while an iterator into it is live.
+                    existing->second = 0;
+                }
+            }
+            for (const auto& entry : inputs.glFormatByUniformName) {
+                if (entry.second == 0) inputs.conflictedNames.push_back(entry.first);
+            }
+            for (const auto& conflicted : inputs.conflictedNames) {
+                inputs.glFormatByUniformName.erase(conflicted);
+            }
+            // Split off the ones SPIRV-Cross will not print. They cannot go through the module -
+            // it throws for them when targeting ESSL, and the stage is lost - so they are spelled
+            // into the emitted text instead. Collected first, erased after, because a flat hash
+            // map must not be restructured while it is being walked.
+            Vector<String> textCompleted;
+            for (const auto& entry : inputs.glFormatByUniformName) {
+                if (MG_Util::ShaderTranspiler::ShaderCompiler::SpirvCrossCanPrintEsslImageFormat(entry.second)) {
+                    continue;
+                }
+                String spelling = MG_Util::ShaderTranspiler::ShaderCompiler::EsslImageFormatSpelling(entry.second);
+                if (spelling.empty()) continue; // no image-format spelling at all; nothing to write
+                inputs.esslFormatQualifierByUniformName.emplace(entry.first, Move(spelling));
+                textCompleted.push_back(entry.first);
+            }
+            for (const auto& name : textCompleted) {
+                inputs.glFormatByUniformName.erase(name);
+            }
+            return inputs;
+        }
+
+        Uint64 BackendProgramObjectImpl::ComputeImageUnitFormatSignature() const {
+            if (m_formatlessImageUnits.empty()) return 0; // all but a handful of programs
+            Uint64 signature = 0;
+            for (const Int unit : m_formatlessImageUnits) {
+                signature = MixImageUnitFormat(signature, unit, BoundImageUnitFormat(unit));
+            }
+            return signature;
+        }
+
+        Bool BackendProgramObjectImpl::ImageUnitFormatsStillMatch() const {
+            if (m_formatlessImageUnits.empty()) return m_imageUnitFormatSignature == 0;
+            return ComputeImageUnitFormatSignature() == m_imageUnitFormatSignature;
+        }
+
         void BackendProgramObjectImpl::SyncToBackend(
             const SharedPtr<MG_State::GLState::ProgramObject>& stateProgramObject) {
 #ifdef TRACY_ENABLE
@@ -4537,6 +4692,18 @@ namespace MobileGL::MG_Backend::DirectGLES {
             // this build current - the draw path compares the signature and rebuilds on a change.
             const auto& storageBlockBindingOverrides = stateProgramObject->GetShaderStorageBlockBindingOverrides();
             m_shaderStorageBlockBindingSignature = ComputeShaderStorageBlockBindingSignature(*stateProgramObject);
+            // The same shape again for image FORMATS: what a format-less image declaration
+            // compiles to depends on live glBindImageTexture state, so the pairs it was built
+            // against are recorded here and compared per draw (ImageUnitFormatsStillMatch).
+            // Taken BEFORE the transpile loop so both the bake and the key see one snapshot.
+            const ImageFormatBakeInputs imageFormatBake = CollectImageFormatBakeInputs(*stateProgramObject);
+            m_formatlessImageUnits = imageFormatBake.units;
+            m_imageUnitFormatSignature = imageFormatBake.signature;
+            for (const auto& conflicted : imageFormatBake.conflictedNames) {
+                MGLOG_D("Image uniform '%s' of program %u declares no format and its elements address units with "
+                        "different bound formats; left format-less.",
+                        conflicted.c_str(), stateProgramObject->GetExternalIndex());
+            }
 
             // Detach all existing shaders
             GLint attachedCount = 0;
@@ -4719,6 +4886,25 @@ namespace MobileGL::MG_Backend::DirectGLES {
                     effectiveSpirv = &arrayImageSpirv;
                 }
 
+                // GLSL ES has no format-less image: `writeonly uniform uimage2D` is legal desktop
+                // GLSL 4.2 and an Adreno ES compile error ("all images have to define layout
+                // format"), which loses the whole program. Give each such image the format the
+                // application bound to its unit - the one GL's format-class rules make correct -
+                // so SPIRV-Cross prints a qualifier. AFTER the 1D-array lowering above, which
+                // also rewrites image types, so this one is looking at the final shapes.
+                //
+                // Gated on the module actually declaring one: the map is empty for every program
+                // whose images all declare formats, and the cheap probe keeps a program that has
+                // an unbound format-less image from paying an optimizer round trip per stage.
+                Vector<unsigned int> imageFormatSpirv;
+                if (!imageFormatBake.glFormatByUniformName.empty() &&
+                    MG_Util::ShaderTranspiler::ShaderCompiler::DeclaresFormatlessStorageImage(*effectiveSpirv) &&
+                    MG_Util::ShaderTranspiler::ShaderCompiler::BakeImageFormatsForEssl(
+                        *effectiveSpirv, imageFormatBake.glFormatByUniformName, imageFormatSpirv) &&
+                    !imageFormatSpirv.empty()) {
+                    effectiveSpirv = &imageFormatSpirv;
+                }
+
                 // GLSL ES demands a constant integral expression to index a fragment output
                 // array; SPIR-V does not, so a shader that writes coeff[i] from a loop
                 // reaches SPIRV-Cross intact and comes out as ESSL a strict driver rejects
@@ -4786,8 +4972,24 @@ namespace MobileGL::MG_Backend::DirectGLES {
                 // because a header concern reads better before the body ones.
                 source = RetargetTextureBufferExtension(std::move(source),
                                                         g_GLESCapabilities.TextureBufferSupport);
+                // The other header-level rewrite, and next to that one for the same reason. The
+                // formats it covers are both the ones the bake above put into the module and the
+                // ones the application declared itself - either can be outside the thirteen GLSL
+                // ES has in core, and neither reaches the driver without this directive.
+                source = RequestExtendedImageFormats(std::move(source),
+                                                     imageFormatBake.needsExtendedImageFormats &&
+                                                         g_GLESCapabilities.SupportsExtendedImageFormats);
 
                 source = RebindImageUniformsToFrontendUnits(std::move(source), stateProgramObject);
+                // The completion half of the format bake, for the formats SPIRV-Cross throws on
+                // rather than prints (r8ui and the rest of its desktop-only set). Empty for every
+                // program whose format-less images bound a format the module could carry, which
+                // is the normal case - those were baked into the SPIR-V above and this pass finds
+                // their declarations already qualified. AFTER the rebind, so the layout qualifier
+                // it edits is the one that already exists; BEFORE the split and the binding
+                // strip, so both halves of a split image inherit the format.
+                source = BakeImageFormatQualifiers(std::move(source),
+                                                   imageFormatBake.esslFormatQualifierByUniformName);
                 // Wedged between those two on purpose:
                 //  * AFTER RebindImageUniformsToFrontendUnits, so the binding it copies onto
                 //    both halves of a split image is already the frontend texture unit (and so

MobileGL/MG_Backend/DirectGLES/Managers.h

@@ -1122,6 +1122,28 @@ namespace MobileGL::MG_Backend::DirectGLES {
             // stale as one built before a relink - while the sampler half, which really is
             // re-issued per draw, needs nothing of the sort.
             Uint32 GetSyncedImageUnitVersion() const { return m_syncedImageUnitVersion; }
+            // Whether the (unit, bound format) pairs this program's FORMAT-LESS image uniforms
+            // resolve to are still the ones its ESSL was generated against.
+            //
+            // A fourth condition of the same family as the three above, and the only one that
+            // reads live state rather than a program-side counter, because that is where the
+            // dependency actually is. GLSL ES requires a format layout qualifier on every image
+            // where desktop GLSL lets a writeonly declaration omit one, and the only correct
+            // qualifier is whatever glBindImageTexture named - so a declaration with no format
+            // is compiled against the BINDING, and a rebind to a different format makes the
+            // built program wrong. Keyed on the units the program's own images address (cached
+            // at sync, since a unit can only move by glUniform1i, which bumps the image-unit
+            // version above and forces a re-sync anyway), so the cost on a program with no
+            // format-less image - which is all but a handful - is one empty-vector test.
+            //
+            // Deliberately NOT reached from glBindImageTexture: that entry point must never
+            // trigger a build (same constraint as glShaderStorageBlockBinding). It moves the
+            // state and this comparison notices at the next Prepare, which is also what makes
+            // an image first bound AFTER link work.
+            Bool ImageUnitFormatsStillMatch() const;
+            // The value ImageUnitFormatsStillMatch() compares against, recomputed from live
+            // image-unit state. 0 when the program has no format-less image uniform.
+            Uint64 ComputeImageUnitFormatSignature() const;
 
         private:
             void CacheResourceLocations(const SharedPtr<MG_State::GLState::ProgramObject>& stateProgramObject);
@@ -1155,6 +1177,12 @@ namespace MobileGL::MG_Backend::DirectGLES {
             BufferImpl::UboRingAllocation m_globalUboRingAllocation;
             Uint32 m_syncedLinkVersion = ~0u;
             Uint32 m_syncedImageUnitVersion = ~0u;
+            // Image units addressed by the program's FORMAT-LESS image uniforms, and the digest
+            // of the (unit, format) pairs the generated ESSL baked. Empty/0 for every program
+            // that declares a format on all of its images, which is the overwhelming majority -
+            // and what keeps the per-draw comparison free for them.
+            Vector<Int> m_formatlessImageUnits;
+            Uint64 m_imageUnitFormatSignature = 0;
             SamplerPassMemo m_samplerPassMemo;
         };
 
@@ -1198,6 +1226,40 @@ namespace MobileGL::MG_Backend::DirectGLES {
         // already has costs nothing. 0 when nothing was ever rebound.
         Uint64 ComputeShaderStorageBlockBindingSignature(
             const MG_State::GLState::ProgramObject& stateProgramObject);
+
+        // Everything the image-format bake needs from one walk of a program's uniform
+        // reflection. GLSL ES requires a format layout qualifier on every image uniform;
+        // desktop GLSL lets a writeonly (or readonly) declaration omit one, and the only
+        // format that is CORRECT to substitute is whatever glBindImageTexture named for the
+        // unit that uniform addresses - so the transpile bakes it in and the build is keyed
+        // on it.
+        struct ImageFormatBakeInputs {
+            // Uniform name (SPIR-V spelling, i.e. an array named once, unsubscripted) to the GL
+            // internal format to bake. Holds only uniforms that DECLARED no format; a declared
+            // one is authoritative and is never overridden.
+            UnorderedMap<String, Uint> glFormatByUniformName;
+            // The same uniforms whose format SPIRV-Cross REFUSES to print for ESSL (it throws on
+            // its desktop-only set, which loses the stage), paired with the ESSL spelling to
+            // write into the emitted declaration instead. Disjoint from the map above by
+            // construction: a format is baked into the module or completed in the text, never
+            // both. r8ui - the stencil half of the packed_depth_stencil case - lands here.
+            UnorderedMap<String, String> esslFormatQualifierByUniformName;
+            // Units those uniforms address, kept so the draw path can re-read their formats
+            // without walking the reflection again.
+            Vector<Int> units;
+            // Digest of the (unit, format) pairs above. 0 when the program has no format-less
+            // image uniform, which is all but a handful.
+            Uint64 signature = 0;
+            // Array uniforms whose elements resolved to units holding DIFFERENT formats: one
+            // declaration carries one qualifier, so there is nothing correct to bake and they
+            // are dropped from the map above. Kept for diagnostics.
+            Vector<String> conflictedNames;
+            // Some format in play - declared or baked - is outside the GLSL ES core image
+            // format set, so the emitted ESSL needs the GL_NV_image_formats directive.
+            Bool needsExtendedImageFormats = false;
+        };
+        ImageFormatBakeInputs CollectImageFormatBakeInputs(
+            const MG_State::GLState::ProgramObject& stateProgramObject);
     } // namespace PrgramImpl
 
     namespace SamplerImpl {

MobileGL/MG_Backend/DirectGLES/Utils.cpp

@@ -535,6 +535,92 @@ namespace MobileGL::MG_Backend::DirectGLES {
             return glslCode;
         }
 
+        String RequestExtendedImageFormats(String glslCode, Bool needed) {
+#ifdef TRACY_ENABLE
+            ZoneScopedC(TRACY_ZONECOLOR_BACKEND);
+#endif
+            // GLSL ES core has thirteen image formats; GL has forty. SPIRV-Cross prints whatever
+            // format the OpTypeImage carries and asks for no extension for it, so an r8ui or
+            // rg16f image - declared as such, or baked from the bound one - reaches the driver as
+            // a format its core language does not know. GL_NV_image_formats is the only thing
+            // that adds them, and it has to be requested by name.
+            //
+            // The caller decides `needed`: it knows which formats are in play (from the uniform
+            // reflection and the image-unit bindings) and whether the driver advertises the
+            // extension at all - `#extension` on an unadvertised name is itself a hard error, so
+            // this must never be emitted speculatively.
+            static constexpr const char* kDirective = "#extension GL_NV_image_formats : require\n";
+            static constexpr const char* kExtName = "GL_NV_image_formats";
+            if (!needed || glslCode.find(kExtName) != String::npos) {
+                return glslCode;
+            }
+            // After the #version line, which must stay first. Everything else about the header is
+            // order-insensitive, and ForceSupporterOutput's scan for the LAST #extension
+            // directive still finds whichever one that is.
+            const SizeT versionPos = glslCode.find("#version");
+            if (versionPos == String::npos) {
+                return kDirective + glslCode;
+            }
+            const SizeT lineEnd = glslCode.find('\n', versionPos);
+            if (lineEnd == String::npos) {
+                return glslCode + "\n" + kDirective;
+            }
+            glslCode.insert(lineEnd + 1, kDirective);
+            return glslCode;
+        }
+
+        String BakeImageFormatQualifiers(String glslCode,
+                                         const UnorderedMap<String, String>& esslFormatByUniformName) {
+#ifdef TRACY_ENABLE
+            ZoneScopedC(TRACY_ZONECOLOR_BACKEND);
+#endif
+            if (esslFormatByUniformName.empty() || glslCode.find("image") == String::npos) {
+                return glslCode;
+            }
+            // Same declaration shape RebindImageUniformsToFrontendUnits matches, and for the same
+            // reason: one line, one image uniform, the name in group 3.
+            static const std::regex imageDeclRegex(
+                R"((layout\s*\(([^)]*)\)\s*)?uniform\s+(?:(?:readonly|writeonly|coherent|volatile|restrict|highp|mediump|lowp)\s+)*[iu]?image[A-Za-z0-9]+\s+([A-Za-z_][A-Za-z0-9_]*)\s*(\[[^\]]*\])?\s*;)");
+            // Every image format spelling GLSL has, so a declaration that already carries one is
+            // recognised whatever it says - the caller's map is consulted only for declarations
+            // with NO format, never to override a written one.
+            static const std::regex existingFormatRegex(
+                R"(\b(rgba32f|rgba16f|rg32f|rg16f|r11f_g11f_b10f|r32f|r16f|rgba16|rgb10_a2|rg16|rg8|r16|r8|rgba16_snorm|rgba8_snorm|rg16_snorm|rg8_snorm|r16_snorm|r8_snorm|rgba32i|rgba16i|rgba8i|rg32i|rg16i|rg8i|r32i|r16i|r8i|rgba32ui|rgba16ui|rgba8ui|rgb10_a2ui|rg32ui|rg16ui|rg8ui|r32ui|r16ui|r8ui)\b)");
+
+            String result;
+            result.reserve(glslCode.size());
+            SizeT lineStart = 0;
+            while (lineStart <= glslCode.size()) {
+                const SizeT lineEnd = glslCode.find('\n', lineStart);
+                const Bool lastLine = lineEnd == String::npos;
+                String line = glslCode.substr(lineStart, lastLine ? String::npos : lineEnd - lineStart);
+
+                std::smatch match;
+                if (std::regex_search(line, match, imageDeclRegex)) {
+                    const String name = match[3].str();
+                    const auto formatIt = esslFormatByUniformName.find(name);
+                    const String layoutContents = match[2].matched ? match[2].str() : String();
+                    if (formatIt != esslFormatByUniformName.end() && !formatIt->second.empty() &&
+                        !std::regex_search(layoutContents, existingFormatRegex)) {
+                        if (match[1].matched) {
+                            const SizeT layoutOpen = line.find('(', match.position(1));
+                            line.insert(layoutOpen + 1, formatIt->second + ", ");
+                        } else {
+                            line.insert(match.position(0), "layout(" + formatIt->second + ") ");
+                        }
+                    }
+                }
+
+                result += line;
+                if (lastLine) {
+                    break;
+                }
+                result += '\n';
+                lineStart = lineEnd + 1;
+            }
+            return result;
+        }
+
         String RemoveLayoutBinding(const String& glslCode) {
 #ifdef TRACY_ENABLE
             ZoneScopedC(TRACY_ZONECOLOR_BACKEND);

MobileGL/MG_Backend/DirectGLES/Utils.h

@@ -137,6 +137,26 @@ namespace MobileGL::MG_Backend::DirectGLES {
         // ES 3.2 needs no directive at all and an EXT driver already has the right one.
         String RetargetTextureBufferExtension(String glslCode,
                                               MG_External::GLESCapabilities::TextureBufferTier tier);
+        // Adds `#extension GL_NV_image_formats : require` when the shader carries an image
+        // format qualifier GLSL ES has no core spelling for. SPIRV-Cross prints the format and
+        // asks for nothing, so the request has to be made here. `needed` is the caller's answer,
+        // because only it knows which formats are in play AND whether the driver advertises the
+        // extension - requesting an unadvertised extension is itself a compile error, so this is
+        // never emitted speculatively. A no-op when not needed or already present.
+        String RequestExtendedImageFormats(String glslCode, Bool needed);
+        // Writes a format layout qualifier into the image declarations named in
+        // `esslFormatByUniformName` that still have none. The completion half of the image-format
+        // bake, and ONLY that: the SPIR-V pass (BakeImageFormatsPass) is what normally puts the
+        // format in, but SPIRV-Cross throws rather than printing the formats it calls
+        // desktop-only when it targets ESSL - r8ui among them, which is what the stencil half of
+        // KHR-GL4x.packed_depth_stencil.stencil_texturing binds - and a throw loses the whole
+        // stage. So those formats stay out of the module and are spelled here instead, on the
+        // emitted text, where nothing can refuse them.
+        //
+        // Declarations that already carry a format are left exactly as they are, whoever wrote
+        // it. Must run before RemoveLayoutBinding, which is where an image's layout qualifier
+        // stops being safe to edit by hand.
+        String BakeImageFormatQualifiers(String glslCode, const UnorderedMap<String, String>& esslFormatByUniformName);
         String RemoveLayoutBinding(const String& glslCode);
         // Prefix of the writeonly half a read+write image uniform is split into (see
         // SplitReadWriteImageUniforms); the suffix is the image's own name.