[Fix] (Program): count the tessellation control stage as a transform-feedback capture stage

MobileGL/MG_State/GLState/Core.cpp

@@ -710,8 +710,15 @@ namespace MobileGL::MG_State {
             //     must not, or failing the link and killing every draw. A capture stage with an
             //     empty list is not a reason to look further down: it is the answer, and
             //     glBeginTransformFeedback's INVALID_OPERATION is the correct consequence.
+            //
+            // The order is the pipeline read backwards and includes the tessellation CONTROL
+            // stage, which is a vertex-processing stage too (GL 4.6 core 11): it can only be
+            // the last one in a pipeline that has a TCS but no evaluation or geometry stage,
+            // which is why it sits after TessEval. Same four stages, same order, as
+            // ProgramLinkTask::ResolveTransformFeedbackVaryings - see rule (2).
             for (const ShaderStage captureStage:
-                 {ShaderStage::Geometry, ShaderStage::TessEval, ShaderStage::Vertex}) {
+                 {ShaderStage::Geometry, ShaderStage::TessEval, ShaderStage::TessControl,
+                  ShaderStage::Vertex}) {
                 if (!compositeHasStage[static_cast<SizeT>(captureStage)]) continue;
                 const auto& captureProgram = pipeline->GetStageProgram(captureStage);
                 if (!captureProgram) continue;

MobileGL/MG_State/GLState/ProgramState/ProgramLinkTask.cpp

@@ -1910,10 +1910,18 @@ namespace MobileGL::MG_State::GLState {
             return true;
         }
 
-        // Capture happens at the last vertex-processing stage (geometry, then
+        // Capture happens at the last vertex-processing stage (geometry, then tessellation
-        // tessellation evaluation, then vertex).
+        // evaluation, then tessellation CONTROL, then vertex). All four are vertex-processing
+        // stages in GL 4.6 core 11 - the control shader included - and in a separable program
+        // whose only stage is a TCS it is the last one that exists, so it is the capture stage
+        // and such a program MUST link (GL 4.6 core 7.3/11.1.2.1; the conformance suite spells
+        // the API split out at esextcTessellationShaderXFB.cpp:390-416, where a non-ES context
+        // takes should_succeed=true). TessControl sits AFTER TessEvaluation so a complete
+        // pipeline still captures at the evaluation stage and only a TCS-only program falls
+        // through to it. If MobileGL ever serves an ES context this arm has to be gated on the
+        // advertised API: ES requires the very same link to FAIL.
         const glslang::TIntermediate* captureIntermediate = nullptr;
-        for (EShLanguage stage : {EShLangGeometry, EShLangTessEvaluation, EShLangVertex}) {
+        for (EShLanguage stage : {EShLangGeometry, EShLangTessEvaluation, EShLangTessControl, EShLangVertex}) {
             captureIntermediate = artifacts.program->getIntermediate(stage);
             if (captureIntermediate != nullptr) {
                 break;

MobileGL/MG_State/GLState/ProgramState/ProgramObject.cpp

@@ -554,7 +554,8 @@ namespace MobileGL::MG_State::GLState {
         // asked for is the safer of the two readings.
         if (task->in.requestedXfbVaryings.empty()) {
             for (const ShaderStage captureStage:
-                 {ShaderStage::Geometry, ShaderStage::TessEval, ShaderStage::Vertex}) {
+                 {ShaderStage::Geometry, ShaderStage::TessEval, ShaderStage::TessControl,
+                  ShaderStage::Vertex}) {
                 Bool stagePresent = false;
                 for (const auto& shader : m_shaders) {
                     if (!shader || shader->GetShaderStage() != captureStage) continue;

MobileGL/MG_Test/Program/CMakeLists.txt

@@ -180,6 +180,22 @@ target_link_libraries(
         ${LINK_LIBRARIES}
 )
 
+add_executable(
+        TessellationLinkTest
+        TessellationLinkTest.cpp
+)
+
+target_include_directories(TessellationLinkTest PRIVATE
+        ${MGL_ROOT}/include
+        ${MGL_ROOT}/MobileGL
+)
+
+target_link_libraries(
+        TessellationLinkTest PRIVATE
+        GTest::gtest_main
+        ${LINK_LIBRARIES}
+)
+
 add_executable(
         ProgramPipelineCompositeTest
         ProgramPipelineCompositeTest.cpp
@@ -229,6 +245,7 @@ gtest_discover_tests(ProgramTest DISCOVERY_TIMEOUT 30 PROPERTIES LABELS unit)
 gtest_discover_tests(ProgramInterfaceTest DISCOVERY_TIMEOUT 30 PROPERTIES LABELS unit)
 gtest_discover_tests(ProgramPipelineCompositeTest DISCOVERY_TIMEOUT 30 PROPERTIES LABELS unit)
 gtest_discover_tests(XfbBlockVaryingTest DISCOVERY_TIMEOUT 30 PROPERTIES LABELS unit)
+gtest_discover_tests(TessellationLinkTest DISCOVERY_TIMEOUT 30 PROPERTIES LABELS unit)
 # Heavier than the rest of the unit suite by design: several cases deliberately saturate the
 # compile pool so there is something in flight to race against.
 gtest_discover_tests(AsyncCompileTest DISCOVERY_TIMEOUT 60 PROPERTIES LABELS unit TIMEOUT 300)

MobileGL/MG_Test/Program/TessellationLinkTest.cpp

@@ -0,0 +1,288 @@
+// MobileGL - MobileGL/MG_Test/Program/TessellationLinkTest.cpp
+// Copyright (c) 2025-2026 MobileGL-Dev
+// Licensed under the GNU Lesser General Public License v3.0:
+//   https://www.gnu.org/licenses/gpl-3.0.txt
+//   https://www.gnu.org/licenses/lgpl-3.0.txt
+// SPDX-License-Identifier: LGPL-3.0-only
+// End of Source File Header
+
+// Link-time properties of programs that carry a tessellation control stage. GPU-free:
+// everything asserted here is a property of the link, not of any driver.
+//
+// Two independent defects live here, both found by KHR-GL4x.tessellation_shader:
+//
+//  (1) The transform-feedback capture stage. GL 4.6 core 11 makes the tessellation CONTROL
+//      shader a vertex-processing stage like the other three, so in a separable program whose
+//      only stage is a TCS it is the LAST vertex-processing stage and therefore the capture
+//      stage - such a program must link with transform-feedback varyings requested. MobileGL
+//      searched {geometry, tessellation evaluation, vertex} only and refused the link with
+//      "Transform feedback varyings requested but the program has no vertex-processing stage",
+//      failing KHR-GL4x.tessellation_shader.single.xfb_captures_data_from_correct_stage on all
+//      three API versions (esextcTessellationShaderXFB.cpp:390-416 passes should_succeed=true
+//      for a non-ES context; ES demands the opposite, which is why the new arm is documented as
+//      desktop-GL-only at the search site).
+//
+//  (2) `patch out T name[N]` against `patch in T name[N]`. Legal, identically spelled on both
+//      sides, and rejected - see the last case, which carries the diagnosis.
+
+#include <gtest/gtest.h>
+
+#include <string>
+#include <vector>
+
+#include "Includes.h"
+#include "Init.h"
+#include "MG_Impl/GLImpl/Getter/GL_Getter.h"
+#include "MG_Impl/GLImpl/Program/GL_Program.h"
+#include "MG_State/GLState/Core.h"
+
+using namespace MobileGL;
+using namespace MobileGL::MG_Impl::GLImpl;
+
+namespace {
+    class TessellationLinkTest: public ::testing::Test {
+    protected:
+        void SetUp() override {
+            MobileGL::Initialize();
+            for (int i = 0; i < 32 && GetError() != GL_NO_ERROR; ++i) {
+            }
+        }
+    };
+
+    std::string ShaderLog(GLuint shader) {
+        char log[4096] = "";
+        GetShaderInfoLog(shader, sizeof(log), nullptr, log);
+        return std::string(log);
+    }
+
+    std::string LinkLog(GLuint program) {
+        char log[4096] = "";
+        GetProgramInfoLog(program, sizeof(log), nullptr, log);
+        return std::string(log);
+    }
+
+    GLint Programiv(GLuint program, GLenum pname) {
+        GLint value = -1;
+        GetProgramiv(program, pname, &value);
+        return value;
+    }
+
+    // Attaches one compiled shader of each requested stage. Compilation is asserted, so a
+    // failure here is a shader bug in the test rather than a link result.
+    GLuint MakeProgram(const std::vector<std::pair<GLenum, const char*>>& stages, Bool separable) {
+        const GLuint program = CreateProgram();
+        if (separable) {
+            ProgramParameteri(program, GL_PROGRAM_SEPARABLE, GL_TRUE);
+        }
+        for (const auto& [type, source]: stages) {
+            const GLuint shader = CreateShader(type);
+            ShaderSource(shader, 1, &source, nullptr);
+            CompileShader(shader);
+            GLint compiled = GL_FALSE;
+            GetShaderiv(shader, GL_COMPILE_STATUS, &compiled);
+            EXPECT_EQ(compiled, GL_TRUE) << "stage 0x" << std::hex << type << "\n" << ShaderLog(shader);
+            AttachShader(program, shader);
+        }
+        return program;
+    }
+
+    // The conformance suite's own tessellation control shader
+    // (esextcTessellationShaderXFB.cpp:360-381), with the ES-only ${...} expansions dropped -
+    // on a desktop context they expand to nothing.
+    constexpr const char* kCtsTessControl = R"(#version 460 core
+layout (vertices=4) out;
+
+in  BLOCK_INOUT { vec4 value; } user_in[];
+out BLOCK_INOUT { vec4 value; } user_out[];
+
+void main()
+{
+    gl_out   [gl_InvocationID].gl_Position = vec4(0.0, 0.0, 0.0, 1.0);
+    user_out [gl_InvocationID].value       = vec4(2.0, 3.0, 4.0, 5.0);
+
+    gl_TessLevelOuter[0] = 1.0;
+    gl_TessLevelOuter[1] = 1.0;
+}
+)";
+
+    // A tessellation control shader IS a vertex-processing stage (GL 4.6 core 11), and in a
+    // TCS-only separable program it is the last one - so it is the capture stage and the link
+    // must succeed with the block member resolved against ITS outputs.
+    TEST_F(TessellationLinkTest, TcsOnlySeparableProgramWithXfbVaryingsLinks) {
+        const GLuint program = MakeProgram({{GL_TESS_CONTROL_SHADER, kCtsTessControl}}, /*separable=*/true);
+        const GLchar* const varyings[1] = {"BLOCK_INOUT.value"};
+        TransformFeedbackVaryings(program, 1, varyings, GL_SEPARATE_ATTRIBS);
+        LinkProgram(program);
+
+        ASSERT_EQ(Programiv(program, GL_LINK_STATUS), GL_TRUE) << LinkLog(program);
+        EXPECT_EQ(GetError(), static_cast<GLenum>(GL_NO_ERROR));
+
+        // The request resolved rather than being quietly dropped: the interface reports it back.
+        EXPECT_EQ(Programiv(program, GL_TRANSFORM_FEEDBACK_VARYINGS), 1);
+        EXPECT_EQ(Programiv(program, GL_TRANSFORM_FEEDBACK_BUFFER_MODE), GL_SEPARATE_ATTRIBS);
+
+        GLchar name[128] = {'\0'};
+        GLsizei length = 0;
+        GLsizei size = 0;
+        GLenum type = 0;
+        GetTransformFeedbackVarying(program, 0, sizeof(name), &length, &size, &type, name);
+        EXPECT_EQ(std::string(name, name + (length < 0 ? 0 : length)), "BLOCK_INOUT.value");
+        EXPECT_EQ(type, static_cast<GLenum>(GL_FLOAT_VEC4));
+        EXPECT_EQ(GetError(), static_cast<GLenum>(GL_NO_ERROR));
+    }
+
+    // Control: the same program with no capture request. It linked before the fix too, which is
+    // what keeps this case honest about WHICH half of the link moved.
+    TEST_F(TessellationLinkTest, TcsOnlySeparableProgramWithoutXfbVaryingsLinks) {
+        const GLuint program = MakeProgram({{GL_TESS_CONTROL_SHADER, kCtsTessControl}}, /*separable=*/true);
+        LinkProgram(program);
+        ASSERT_EQ(Programiv(program, GL_LINK_STATUS), GL_TRUE) << LinkLog(program);
+        EXPECT_EQ(Programiv(program, GL_TRANSFORM_FEEDBACK_VARYINGS), 0);
+        EXPECT_EQ(GetError(), static_cast<GLenum>(GL_NO_ERROR));
+    }
+
+    // A program with no vertex-processing stage at all still has to be refused - the fix widened
+    // the search, it did not remove the check.
+    TEST_F(TessellationLinkTest, FragmentOnlySeparableProgramWithXfbVaryingsStillFailsToLink) {
+        constexpr const char* fs = R"(#version 460 core
+out vec4 color;
+void main() { color = vec4(1.0); }
+)";
+        const GLuint program = MakeProgram({{GL_FRAGMENT_SHADER, fs}}, /*separable=*/true);
+        const GLchar* const varyings[1] = {"color"};
+        TransformFeedbackVaryings(program, 1, varyings, GL_INTERLEAVED_ATTRIBS);
+        LinkProgram(program);
+        EXPECT_EQ(Programiv(program, GL_LINK_STATUS), GL_FALSE);
+        EXPECT_NE(LinkLog(program).find("no vertex-processing stage"), std::string::npos) << LinkLog(program);
+        for (int i = 0; i < 32 && GetError() != GL_NO_ERROR; ++i) {
+        }
+    }
+
+    constexpr const char* kPassthroughVs = R"(#version 460 core
+void main() { gl_Position = vec4(0.0, 0.0, 0.0, 1.0); }
+)";
+
+    constexpr const char* kTcsWithPatchScalar = R"(#version 460 core
+layout (vertices = 3) out;
+patch out vec4 tcs_patch;
+out vec4 tcs_per_vertex[];
+void main() {
+    tcs_patch = vec4(1.0);
+    tcs_per_vertex[gl_InvocationID] = vec4(2.0);
+    gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;
+    gl_TessLevelOuter[0] = 1.0; gl_TessLevelOuter[1] = 1.0; gl_TessLevelOuter[2] = 1.0;
+    gl_TessLevelInner[0] = 1.0;
+}
+)";
+
+    constexpr const char* kTesWithPatchScalar = R"(#version 460 core
+layout (triangles) in;
+patch in vec4 tcs_patch;
+in vec4 tcs_per_vertex[];
+out vec4 tes_out;
+void main() {
+    tes_out = tcs_patch + tcs_per_vertex[0];
+    gl_Position = gl_in[0].gl_Position;
+}
+)";
+
+    // The capture stage of a COMPLETE pipeline is unchanged by the widened search: tessellation
+    // control sits AFTER tessellation evaluation in the order, so a program that has both still
+    // resolves its capture names against the EVALUATION stage's outputs. Both halves are pinned -
+    // an evaluation output resolves, a control output does not.
+    TEST_F(TessellationLinkTest, CompletePipelineStillCapturesAtTheEvaluationStage) {
+        {
+            const GLuint program = MakeProgram({{GL_VERTEX_SHADER, kPassthroughVs},
+                                                {GL_TESS_CONTROL_SHADER, kTcsWithPatchScalar},
+                                                {GL_TESS_EVALUATION_SHADER, kTesWithPatchScalar}},
+                                               /*separable=*/true);
+            const GLchar* const varyings[1] = {"tes_out"};
+            TransformFeedbackVaryings(program, 1, varyings, GL_INTERLEAVED_ATTRIBS);
+            LinkProgram(program);
+            ASSERT_EQ(Programiv(program, GL_LINK_STATUS), GL_TRUE) << LinkLog(program);
+            EXPECT_EQ(Programiv(program, GL_TRANSFORM_FEEDBACK_VARYINGS), 1);
+        }
+        {
+            // tcs_per_vertex is an output of the CONTROL stage, which is not the capture stage
+            // here. Resolving it would mean capturing at the wrong stage, so the link must fail.
+            const GLuint program = MakeProgram({{GL_VERTEX_SHADER, kPassthroughVs},
+                                                {GL_TESS_CONTROL_SHADER, kTcsWithPatchScalar},
+                                                {GL_TESS_EVALUATION_SHADER, kTesWithPatchScalar}},
+                                               /*separable=*/true);
+            const GLchar* const varyings[1] = {"tcs_per_vertex"};
+            TransformFeedbackVaryings(program, 1, varyings, GL_INTERLEAVED_ATTRIBS);
+            LinkProgram(program);
+            EXPECT_EQ(Programiv(program, GL_LINK_STATUS), GL_FALSE) << LinkLog(program);
+        }
+        for (int i = 0; i < 32 && GetError() != GL_NO_ERROR; ++i) {
+        }
+    }
+
+    // A patch-qualified SCALAR crosses the TCS/TES boundary today. It is the control for the
+    // array case below: same qualifier, same stages, only the arrayness differs.
+    TEST_F(TessellationLinkTest, PatchQualifiedScalarLinksAcrossTheTessellationStages) {
+        const GLuint program = MakeProgram({{GL_VERTEX_SHADER, kPassthroughVs},
+                                            {GL_TESS_CONTROL_SHADER, kTcsWithPatchScalar},
+                                            {GL_TESS_EVALUATION_SHADER, kTesWithPatchScalar}},
+                                           /*separable=*/true);
+        LinkProgram(program);
+        ASSERT_EQ(Programiv(program, GL_LINK_STATUS), GL_TRUE) << LinkLog(program);
+        EXPECT_EQ(GetError(), static_cast<GLenum>(GL_NO_ERROR));
+    }
+
+    // `patch out int a[N]` against `patch in int a[N]`: legal GLSL, identical spellings, and
+    // currently refused by the VENDORED glslang with "Array sizes must be compatible" while
+    // printing the two sides as the same type. This is what fails
+    // KHR-GL4x.tessellation_shader.tessellation_shader_tc_barriers.* on all three API versions.
+    //
+    // The defect is one asymmetric clause in glslang, not in MobileGL:
+    // 3rdparty/glslang/glslang/MachineIndependent/linkValidate.cpp, TIntermediate::isIoResizeArray.
+    // The TessControl arm is guarded with `&& ! type.getQualifier().patch`; the TessEvaluation arm
+    // is not. A patch-qualified array therefore answers false on the control side and true on the
+    // evaluation side, and the caller's dimension arithmetic (linkValidate.cpp:1200-1218) computes
+    // (numDim - firstDim) == (unitNumDim - unitFirstDim) as (1 - 0) == (1 - 1), i.e. false. The fix
+    // is to mirror the control arm - add `&& ! type.getQualifier().patch` to the TessEvaluation
+    // clause - which belongs in the fork (and upstream), so it is deliberately not made here.
+    //
+    // Written to flip from skip to assertion the moment that lands: the skip is allowed ONLY for
+    // the exact known message, and any other failure is a real failure.
+    TEST_F(TessellationLinkTest, PatchQualifiedArrayLinksAcrossTheTessellationStages) {
+        constexpr const char* tcs = R"(#version 460 core
+layout (vertices = 3) out;
+patch out int tcs_patch_result[16];
+void main() {
+    for (int i = 0; i < 16; ++i) { tcs_patch_result[i] = i; }
+    gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;
+    gl_TessLevelOuter[0] = 1.0; gl_TessLevelOuter[1] = 1.0; gl_TessLevelOuter[2] = 1.0;
+    gl_TessLevelInner[0] = 1.0;
+}
+)";
+        constexpr const char* tes = R"(#version 460 core
+layout (triangles) in;
+patch in int tcs_patch_result[16];
+out vec4 tes_out;
+void main() {
+    tes_out = vec4(float(tcs_patch_result[0] + tcs_patch_result[15]));
+    gl_Position = gl_in[0].gl_Position;
+}
+)";
+        const GLuint program = MakeProgram({{GL_VERTEX_SHADER, kPassthroughVs},
+                                            {GL_TESS_CONTROL_SHADER, tcs},
+                                            {GL_TESS_EVALUATION_SHADER, tes}},
+                                           /*separable=*/true);
+        LinkProgram(program);
+        const std::string log = LinkLog(program);
+        if (Programiv(program, GL_LINK_STATUS) != GL_TRUE &&
+            log.find("Array sizes must be compatible") != std::string::npos) {
+            for (int i = 0; i < 32 && GetError() != GL_NO_ERROR; ++i) {
+            }
+            GTEST_SKIP() << "vendored glslang still credits the TessEvaluation side of a "
+                            "patch-qualified array with an implicit outer dimension "
+                            "(linkValidate.cpp isIoResizeArray, TessEvaluation arm missing "
+                            "`&& ! type.getQualifier().patch`); link log:\n"
+                         << log;
+        }
+        ASSERT_EQ(Programiv(program, GL_LINK_STATUS), GL_TRUE) << log;
+        EXPECT_EQ(GetError(), static_cast<GLenum>(GL_NO_ERROR));
+    }
+} // namespace