[Feat] (MG_Impl, MG_State): implement the framebuffer parameter getters and setters

glFramebufferParameteri, glGetFramebufferParameteriv and their two by-name
siblings were all export stubs - the GL_ARB_framebuffer_no_attachments entry
points. The stub raises no error and writes nothing, so
direct_state_access.framebuffers_get_parameter_errors saw GL_NO_ERROR for all
three conditions it checks.

FramebufferObject gains the five DEFAULT_* parameters as real state, initialised
to GL 4.6 core table 23.24 and bumping the object version on a write like the
read buffer does. The getter answers those plus the six derived names -
GL_SAMPLES and GL_SAMPLE_BUFFERS from the attachments' sample counts,
GL_IMPLEMENTATION_COLOR_READ_FORMAT/_TYPE from the read buffer's internal format,
GL_DOUBLEBUFFER true only for the window-system framebuffer, GL_STEREO false
because stereo surfaces are not exposed - which is what glGetIntegerv already
reports for the bound framebuffer.

The pname rules live in ValidateFramebufferParameterPname, and their ORDER is
load-bearing: a name outside the table is INVALID_ENUM, and only a name that IS
in the table but that the default framebuffer cannot answer is INVALID_OPERATION.
Testing the framebuffer kind first would answer INVALID_ENUM for
GL_FRAMEBUFFER_DEFAULT_WIDTH on framebuffer zero, which is exactly the third
thing the case checks. The by-name forms take zero as the default framebuffer,
like the other DSA framebuffer entry points.

Rendering to a framebuffer with no attachments is deliberately NOT enabled by
this: CheckCompleteness still reports INCOMPLETE_MISSING_ATTACHMENT, because no
backend can rasterize one. The state is real and the queries are honest; the
draw path is a separate piece of work.

Takes framebuffers_get_parameter_errors from failing to passing on both backends,
with framebuffers_get_parameters - which passed only because both getters were
stubs leaving the CTS's zero-initialised comparands untouched - still passing.

MobileGL/MG_Impl/GLImpl/Exporting/Definitions.cpp

@@ -310,8 +310,8 @@ DECLARE_GL_FUNCTION_HEAD(void, DispatchCompute, GLuint num_groups_x, GLuint num_
 DECLARE_GL_FUNCTION_HEAD(void, DispatchComputeIndirect, GLintptr indirect) DECLARE_GL_FUNCTION_END_NO_RETURN(void, DispatchComputeIndirect, indirect)
 DECLARE_GL_FUNCTION_HEAD(void, DrawArraysIndirect, GLenum mode, const void* indirect) DECLARE_GL_FUNCTION_END_NO_RETURN(void, DrawArraysIndirect, mode, indirect)
 DECLARE_GL_FUNCTION_HEAD(void, DrawElementsIndirect, GLenum mode, GLenum type, const void* indirect) DECLARE_GL_FUNCTION_END_NO_RETURN(void, DrawElementsIndirect, mode, type, indirect)
-DECLARE_GL_FUNCTION_STUB_HEAD(void, FramebufferParameteri, GLenum target, GLenum pname, GLint param) DECLARE_GL_FUNCTION_STUB_END_NO_RETURN(void, FramebufferParameteri, target, pname, param)
-DECLARE_GL_FUNCTION_STUB_HEAD(void, GetFramebufferParameteriv, GLenum target, GLenum pname, GLint* params) DECLARE_GL_FUNCTION_STUB_END_NO_RETURN(void, GetFramebufferParameteriv, target, pname, params)
+DECLARE_GL_FUNCTION_HEAD(void, FramebufferParameteri, GLenum target, GLenum pname, GLint param) DECLARE_GL_FUNCTION_END_NO_RETURN(void, FramebufferParameteri, target, pname, param)
+DECLARE_GL_FUNCTION_HEAD(void, GetFramebufferParameteriv, GLenum target, GLenum pname, GLint* params) DECLARE_GL_FUNCTION_END_NO_RETURN(void, GetFramebufferParameteriv, target, pname, params)
 DECLARE_GL_FUNCTION_HEAD(void, GetProgramInterfaceiv, GLuint program, GLenum programInterface, GLenum pname, GLint* params) DECLARE_GL_FUNCTION_END_NO_RETURN(void, GetProgramInterfaceiv, program, programInterface, pname, params)
 DECLARE_GL_FUNCTION_HEAD(GLuint, GetProgramResourceIndex, GLuint program, GLenum programInterface, const GLchar* name) DECLARE_GL_FUNCTION_END(GLuint, GetProgramResourceIndex, program, programInterface, name)
 DECLARE_GL_FUNCTION_HEAD(void, GetProgramResourceName, GLuint program, GLenum programInterface, GLuint index, GLsizei bufSize, GLsizei* length, GLchar* name) DECLARE_GL_FUNCTION_END_NO_RETURN(void, GetProgramResourceName, program, programInterface, index, bufSize, length, name)
@@ -1028,7 +1028,7 @@ DECLARE_GL_FUNCTION_HEAD(void, GetNamedBufferPointerv, GLuint buffer, GLenum pna
 DECLARE_GL_FUNCTION_HEAD(void, GetNamedBufferSubData, GLuint buffer, GLintptr offset, GLsizeiptr size, void* data) DECLARE_GL_FUNCTION_END_NO_RETURN(void, GetNamedBufferSubData, buffer, offset, size, data)
 DECLARE_GL_FUNCTION_HEAD(void, CreateFramebuffers, GLsizei n, GLuint* framebuffers) DECLARE_GL_FUNCTION_END_NO_RETURN(void, CreateFramebuffers, n, framebuffers)
 DECLARE_GL_FUNCTION_HEAD(void, NamedFramebufferRenderbuffer, GLuint framebuffer, GLenum attachment, GLenum renderbuffertarget, GLuint renderbuffer) DECLARE_GL_FUNCTION_END_NO_RETURN(void, NamedFramebufferRenderbuffer, framebuffer, attachment, renderbuffertarget, renderbuffer)
-DECLARE_GL_FUNCTION_STUB_HEAD(void, NamedFramebufferParameteri, GLuint framebuffer, GLenum pname, GLint param) DECLARE_GL_FUNCTION_STUB_END_NO_RETURN(void, NamedFramebufferParameteri, framebuffer, pname, param)
+DECLARE_GL_FUNCTION_HEAD(void, NamedFramebufferParameteri, GLuint framebuffer, GLenum pname, GLint param) DECLARE_GL_FUNCTION_END_NO_RETURN(void, NamedFramebufferParameteri, framebuffer, pname, param)
 DECLARE_GL_FUNCTION_HEAD(void, NamedFramebufferTexture, GLuint framebuffer, GLenum attachment, GLuint texture, GLint level) DECLARE_GL_FUNCTION_END_NO_RETURN(void, NamedFramebufferTexture, framebuffer, attachment, texture, level)
 DECLARE_GL_FUNCTION_HEAD(void, NamedFramebufferTextureLayer, GLuint framebuffer, GLenum attachment, GLuint texture, GLint level, GLint layer) DECLARE_GL_FUNCTION_END_NO_RETURN(void, NamedFramebufferTextureLayer, framebuffer, attachment, texture, level, layer)
 DECLARE_GL_FUNCTION_HEAD(void, NamedFramebufferDrawBuffer, GLuint framebuffer, GLenum buf) DECLARE_GL_FUNCTION_END_NO_RETURN(void, NamedFramebufferDrawBuffer, framebuffer, buf)
@@ -1042,7 +1042,7 @@ DECLARE_GL_FUNCTION_HEAD(void, ClearNamedFramebufferfv, GLuint framebuffer, GLen
 DECLARE_GL_FUNCTION_HEAD(void, ClearNamedFramebufferfi, GLuint framebuffer, GLenum buffer, GLint drawbuffer, GLfloat depth, GLint stencil) DECLARE_GL_FUNCTION_END_NO_RETURN(void, ClearNamedFramebufferfi, framebuffer, buffer, drawbuffer, depth, stencil)
 DECLARE_GL_FUNCTION_HEAD(void, BlitNamedFramebuffer, GLuint readFramebuffer, GLuint drawFramebuffer, GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1, GLint dstX0, GLint dstY0, GLint dstX1, GLint dstY1, GLbitfield mask, GLenum filter) DECLARE_GL_FUNCTION_END_NO_RETURN(void, BlitNamedFramebuffer, readFramebuffer, drawFramebuffer, srcX0, srcY0, srcX1, srcY1, dstX0, dstY0, dstX1, dstY1, mask, filter)
 DECLARE_GL_FUNCTION_HEAD(GLenum, CheckNamedFramebufferStatus, GLuint framebuffer, GLenum target) DECLARE_GL_FUNCTION_END(GLenum, CheckNamedFramebufferStatus, framebuffer, target)
-DECLARE_GL_FUNCTION_STUB_HEAD(void, GetNamedFramebufferParameteriv, GLuint framebuffer, GLenum pname, GLint* param) DECLARE_GL_FUNCTION_STUB_END_NO_RETURN(void, GetNamedFramebufferParameteriv, framebuffer, pname, param)
+DECLARE_GL_FUNCTION_HEAD(void, GetNamedFramebufferParameteriv, GLuint framebuffer, GLenum pname, GLint* param) DECLARE_GL_FUNCTION_END_NO_RETURN(void, GetNamedFramebufferParameteriv, framebuffer, pname, param)
 DECLARE_GL_FUNCTION_HEAD(void, GetNamedFramebufferAttachmentParameteriv, GLuint framebuffer, GLenum attachment, GLenum pname, GLint* params) DECLARE_GL_FUNCTION_END_NO_RETURN(void, GetNamedFramebufferAttachmentParameteriv, framebuffer, attachment, pname, params)
 DECLARE_GL_FUNCTION_HEAD(void, CreateRenderbuffers, GLsizei n, GLuint* renderbuffers) DECLARE_GL_FUNCTION_END_NO_RETURN(void, CreateRenderbuffers, n, renderbuffers)
 DECLARE_GL_FUNCTION_HEAD(void, NamedRenderbufferStorage, GLuint renderbuffer, GLenum internalformat, GLsizei width, GLsizei height) DECLARE_GL_FUNCTION_END_NO_RETURN(void, NamedRenderbufferStorage, renderbuffer, internalformat, width, height)

MobileGL/MG_Impl/GLImpl/Framebuffer/GL_Framebuffer.cpp

@@ -8,6 +8,7 @@
 
 #include "GL_Framebuffer.h"
 #include "Validators.h"
+#include <MG_Util/Texture/TextureFormatProcessor.h>
 #include "Config.h"
 #include <MG_Backend/BackendObjects.h>
 #include <MG_Util/Metrics/TextureMetrics.h>
@@ -2131,6 +2132,124 @@ namespace MobileGL::MG_Impl::GLImpl {
         return GL_FRAMEBUFFER_COMPLETE;
     }
 
+    // GL_ARB_framebuffer_no_attachments plus the queryable framebuffer state of GL 4.6 core 9.2.3.
+    // The DEFAULT_* half is real state on the framebuffer object; the rest is derived from the
+    // attachments, and matches what glGetIntegerv answers for the bound framebuffer.
+    void GetFramebufferParameteriv_Object(const SharedPtr<MG_State::GLState::FramebufferObject>& framebufferObject,
+                                          GLenum pname, GLint* params, const char* caller) {
+        if (params == nullptr) return;
+        if (!FramebufferImpl::ValidateFramebufferParameterPname(pname, framebufferObject->IsDefaultFramebuffer(),
+                                                                /*forSetter=*/false, caller)) {
+            return;
+        }
+
+        const auto resolveSampleCount = [&]() {
+            GLint maxSamples = 0;
+            for (const auto& attachment : framebufferObject->GetAllAttachmentObjects()) {
+                if (attachment.IsRenderbuffer() && attachment.GetRenderbuffer()) {
+                    maxSamples = std::max(maxSamples, static_cast<GLint>(attachment.GetRenderbuffer()->GetSamples()));
+                } else if (attachment.IsTexture() && attachment.GetTexture()) {
+                    maxSamples = std::max(maxSamples, static_cast<GLint>(attachment.GetTexture()->GetSamples()));
+                }
+            }
+            return maxSamples;
+        };
+
+        switch (pname) {
+        case GL_FRAMEBUFFER_DEFAULT_WIDTH:
+            *params = framebufferObject->GetDefaultWidth();
+            break;
+        case GL_FRAMEBUFFER_DEFAULT_HEIGHT:
+            *params = framebufferObject->GetDefaultHeight();
+            break;
+        case GL_FRAMEBUFFER_DEFAULT_LAYERS:
+            *params = framebufferObject->GetDefaultLayers();
+            break;
+        case GL_FRAMEBUFFER_DEFAULT_SAMPLES:
+            *params = framebufferObject->GetDefaultSamples();
+            break;
+        case GL_FRAMEBUFFER_DEFAULT_FIXED_SAMPLE_LOCATIONS:
+            *params = framebufferObject->GetDefaultFixedSampleLocations() ? GL_TRUE : GL_FALSE;
+            break;
+        case GL_SAMPLES:
+            *params = resolveSampleCount();
+            break;
+        case GL_SAMPLE_BUFFERS:
+            *params = resolveSampleCount() > 0 ? 1 : 0;
+            break;
+        case GL_IMPLEMENTATION_COLOR_READ_FORMAT:
+        case GL_IMPLEMENTATION_COLOR_READ_TYPE: {
+            const auto readBuffer = framebufferObject->GetReadBuffer();
+            TextureInternalFormat internalFormat = TextureInternalFormat::Unknown;
+            if (readBuffer != FramebufferAttachmentType::None) {
+                const auto& attachment = framebufferObject->GetAttachment(readBuffer);
+                if (attachment.IsTexture() && attachment.GetTexture()) {
+                    internalFormat = attachment.GetTexture()->GetFormat();
+                } else if (attachment.IsRenderbuffer() && attachment.GetRenderbuffer()) {
+                    internalFormat = attachment.GetRenderbuffer()->GetInternalFormat();
+                }
+            }
+            if (internalFormat == TextureInternalFormat::Unknown) {
+                *params = 0;
+                break;
+            }
+            const GLenum glInternalFormat = MG_Util::ConvertTextureInternalFormatToGLEnum(internalFormat);
+            GLenum normalizedInternalFormat = glInternalFormat;
+            GLenum format = GL_RGBA;
+            GLenum type = GL_UNSIGNED_BYTE;
+            MG_Util::TextureFormatProcessor::NormalizePixelFormat(glInternalFormat, PixelFormatNormalizeOptionBit::None,
+                                                                  &normalizedInternalFormat, &format, &type);
+            *params = static_cast<GLint>(pname == GL_IMPLEMENTATION_COLOR_READ_FORMAT ? format : type);
+            break;
+        }
+        case GL_DOUBLEBUFFER:
+            // Only the window-system surface is ever double buffered; a framebuffer object never is.
+            *params = framebufferObject->IsDefaultFramebuffer() ? GL_TRUE : GL_FALSE;
+            break;
+        case GL_STEREO:
+            // Stereo surfaces are not exposed, matching what glGetIntegerv reports.
+            *params = GL_FALSE;
+            break;
+        default:
+            break;
+        }
+    }
+
+    void FramebufferParameteri_Object(const SharedPtr<MG_State::GLState::FramebufferObject>& framebufferObject,
+                                      GLenum pname, GLint param, const char* caller) {
+        if (!FramebufferImpl::ValidateFramebufferParameterPname(pname, framebufferObject->IsDefaultFramebuffer(),
+                                                                /*forSetter=*/true, caller)) {
+            return;
+        }
+        if (pname != GL_FRAMEBUFFER_DEFAULT_FIXED_SAMPLE_LOCATIONS && param < 0) {
+            MG_State::pGLContext->RecordError(
+                ErrorCode::InvalidValue,
+                MakeUnique<GenericErrorInfo>("MG_Impl/GLImpl", caller,
+                                             "Framebuffer default parameters must be non-negative."));
+            return;
+        }
+
+        switch (pname) {
+        case GL_FRAMEBUFFER_DEFAULT_WIDTH:
+            framebufferObject->SetDefaultWidth(param);
+            break;
+        case GL_FRAMEBUFFER_DEFAULT_HEIGHT:
+            framebufferObject->SetDefaultHeight(param);
+            break;
+        case GL_FRAMEBUFFER_DEFAULT_LAYERS:
+            framebufferObject->SetDefaultLayers(param);
+            break;
+        case GL_FRAMEBUFFER_DEFAULT_SAMPLES:
+            framebufferObject->SetDefaultSamples(param);
+            break;
+        case GL_FRAMEBUFFER_DEFAULT_FIXED_SAMPLE_LOCATIONS:
+            framebufferObject->SetDefaultFixedSampleLocations(param != GL_FALSE);
+            break;
+        default:
+            break;
+        }
+    }
+
     void GetFramebufferAttachmentParameteriv_Object(
         const SharedPtr<MG_State::GLState::FramebufferObject>& framebufferObject, GLenum attachment, GLenum pname,
         GLint* params, const char* caller) {
@@ -2250,6 +2369,54 @@ namespace MobileGL::MG_Impl::GLImpl {
                                                   "GetNamedFramebufferAttachmentParameteriv_State");
     }
 
+    // The by-target forms resolve the binding; the by-name forms take zero as the default
+    // framebuffer, exactly as the other DSA framebuffer entry points do (GL 4.6 core 9.2.3).
+    void GetFramebufferParameteriv_State(GLenum target, GLenum pname, GLint* params) {
+        if (target == GL_FRAMEBUFFER) target = GL_DRAW_FRAMEBUFFER;
+        const auto framebufferTarget = MG_Util::ConvertGLEnumToFramebufferTarget(target);
+        if (!FramebufferImpl::ValidateFramebufferTarget(framebufferTarget)) return;
+        auto& framebufferObject = MG_State::pGLContext->GetFramebufferBindingSlot(framebufferTarget).GetBoundObject();
+        if (!framebufferObject) {
+            MG_State::pGLContext->RecordError(
+                ErrorCode::InvalidOperation,
+                MakeUnique<GenericErrorInfo>("MG_Impl/GLImpl", "GetFramebufferParameteriv_State",
+                                             "Framebuffer target is bound to no framebuffer object."));
+            return;
+        }
+        GetFramebufferParameteriv_Object(framebufferObject, pname, params, "GetFramebufferParameteriv_State");
+    }
+
+    void FramebufferParameteri_State(GLenum target, GLenum pname, GLint param) {
+        if (target == GL_FRAMEBUFFER) target = GL_DRAW_FRAMEBUFFER;
+        const auto framebufferTarget = MG_Util::ConvertGLEnumToFramebufferTarget(target);
+        if (!FramebufferImpl::ValidateFramebufferTarget(framebufferTarget)) return;
+        auto& framebufferObject = MG_State::pGLContext->GetFramebufferBindingSlot(framebufferTarget).GetBoundObject();
+        if (!framebufferObject) {
+            MG_State::pGLContext->RecordError(
+                ErrorCode::InvalidOperation,
+                MakeUnique<GenericErrorInfo>("MG_Impl/GLImpl", "FramebufferParameteri_State",
+                                             "Framebuffer target is bound to no framebuffer object."));
+            return;
+        }
+        FramebufferParameteri_Object(framebufferObject, pname, param, "FramebufferParameteri_State");
+    }
+
+    void GetNamedFramebufferParameteriv_State(GLuint framebuffer, GLenum pname, GLint* params) {
+        auto framebufferObject = framebuffer == 0
+            ? FramebufferImpl::pDefaultFramebufferInfo->defaultFBO
+            : GetNamedFramebufferObject_State(framebuffer, "GetNamedFramebufferParameteriv_State");
+        if (!framebufferObject) return;
+        GetFramebufferParameteriv_Object(framebufferObject, pname, params, "GetNamedFramebufferParameteriv_State");
+    }
+
+    void NamedFramebufferParameteri_State(GLuint framebuffer, GLenum pname, GLint param) {
+        auto framebufferObject = framebuffer == 0
+            ? FramebufferImpl::pDefaultFramebufferInfo->defaultFBO
+            : GetNamedFramebufferObject_State(framebuffer, "NamedFramebufferParameteri_State");
+        if (!framebufferObject) return;
+        FramebufferParameteri_Object(framebufferObject, pname, param, "NamedFramebufferParameteri_State");
+    }
+
     void BlitNamedFramebuffer_State(GLuint readFramebuffer, GLuint drawFramebuffer, GLint srcX0, GLint srcY0,
                                    GLint srcX1, GLint srcY1, GLint dstX0, GLint dstY0, GLint dstX1, GLint dstY1,
                                    GLbitfield mask, GLenum filter) {
@@ -2896,6 +3063,22 @@ namespace MobileGL::MG_Impl::GLImpl {
         return CheckNamedFramebufferStatus_State(framebuffer, target);
     }
 
+    void GetFramebufferParameteriv(GLenum target, GLenum pname, GLint* params) {
+        GetFramebufferParameteriv_State(target, pname, params);
+    }
+
+    void FramebufferParameteri(GLenum target, GLenum pname, GLint param) {
+        FramebufferParameteri_State(target, pname, param);
+    }
+
+    void GetNamedFramebufferParameteriv(GLuint framebuffer, GLenum pname, GLint* params) {
+        GetNamedFramebufferParameteriv_State(framebuffer, pname, params);
+    }
+
+    void NamedFramebufferParameteri(GLuint framebuffer, GLenum pname, GLint param) {
+        NamedFramebufferParameteri_State(framebuffer, pname, param);
+    }
+
     void GetNamedFramebufferAttachmentParameteriv(GLuint framebuffer, GLenum attachment, GLenum pname, GLint* params) {
         GetNamedFramebufferAttachmentParameteriv_State(framebuffer, attachment, pname, params);
     }

MobileGL/MG_Impl/GLImpl/Framebuffer/GL_Framebuffer.h

@@ -67,6 +67,10 @@ namespace MobileGL::MG_Impl::GLImpl {
     void ClearNamedFramebufferiv(GLuint framebuffer, GLenum buffer, GLint drawbuffer, const GLint* value);
     void ClearNamedFramebufferuiv(GLuint framebuffer, GLenum buffer, GLint drawbuffer, const GLuint* value);
     GLenum CheckNamedFramebufferStatus(GLuint framebuffer, GLenum target);
+    void GetFramebufferParameteriv(GLenum target, GLenum pname, GLint* params);
+    void FramebufferParameteri(GLenum target, GLenum pname, GLint param);
+    void GetNamedFramebufferParameteriv(GLuint framebuffer, GLenum pname, GLint* params);
+    void NamedFramebufferParameteri(GLuint framebuffer, GLenum pname, GLint param);
     void GetNamedFramebufferAttachmentParameteriv(GLuint framebuffer, GLenum attachment, GLenum pname, GLint* params);
     void BlitNamedFramebuffer(GLuint readFramebuffer, GLuint drawFramebuffer, GLint srcX0, GLint srcY0, GLint srcX1,
                               GLint srcY1, GLint dstX0, GLint dstY0, GLint dstX1, GLint dstY1, GLbitfield mask,

MobileGL/MG_Impl/GLImpl/Framebuffer/Validators.cpp

@@ -119,6 +119,58 @@ namespace MobileGL::MG_Impl::GLImpl::FramebufferImpl {
         return false;
     }
 
+    Bool ValidateFramebufferParameterPname(GLenum pname, Bool isDefaultFramebuffer, Bool forSetter,
+                                           const char* caller) {
+        Bool isDefaultParameter = false;
+        switch (pname) {
+        case GL_FRAMEBUFFER_DEFAULT_WIDTH:
+        case GL_FRAMEBUFFER_DEFAULT_HEIGHT:
+        case GL_FRAMEBUFFER_DEFAULT_LAYERS:
+        case GL_FRAMEBUFFER_DEFAULT_SAMPLES:
+        case GL_FRAMEBUFFER_DEFAULT_FIXED_SAMPLE_LOCATIONS:
+            isDefaultParameter = true;
+            break;
+        case GL_DOUBLEBUFFER:
+        case GL_IMPLEMENTATION_COLOR_READ_FORMAT:
+        case GL_IMPLEMENTATION_COLOR_READ_TYPE:
+        case GL_SAMPLES:
+        case GL_SAMPLE_BUFFERS:
+        case GL_STEREO:
+            // Queryable only; glFramebufferParameteri sets none of these.
+            if (forSetter) {
+                MG_State::pGLContext->RecordError(
+                    ErrorCode::InvalidEnum,
+                    MakeUnique<GenericErrorInfo>(
+                        "MG_Impl/GLImpl/FramebufferImpl", caller,
+                        std::format("pname {} is not settable on a framebuffer.",
+                                    MG_Util::ConvertGLEnumToString(pname))));
+                return false;
+            }
+            break;
+        default:
+            MG_State::pGLContext->RecordError(
+                ErrorCode::InvalidEnum,
+                MakeUnique<GenericErrorInfo>(
+                    "MG_Impl/GLImpl/FramebufferImpl", caller,
+                    std::format("pname {} is not a framebuffer parameter.",
+                                MG_Util::ConvertGLEnumToString(pname))));
+            return false;
+        }
+
+        // The default framebuffer has no DEFAULT_* state of its own - its shape comes from the
+        // surface - so those names are accepted enums it simply cannot answer or accept.
+        if (isDefaultFramebuffer && isDefaultParameter) {
+            MG_State::pGLContext->RecordError(
+                ErrorCode::InvalidOperation,
+                MakeUnique<GenericErrorInfo>(
+                    "MG_Impl/GLImpl/FramebufferImpl", caller,
+                    std::format("pname {} does not apply to the default framebuffer.",
+                                MG_Util::ConvertGLEnumToString(pname))));
+            return false;
+        }
+        return true;
+    }
+
     Bool ValidateReadFramebufferForCopy(const char* caller) {
         auto& framebufferObject =
             MG_State::pGLContext->GetFramebufferBindingSlot(FramebufferTarget::Read).GetBoundObject();

MobileGL/MG_Impl/GLImpl/Framebuffer/Validators.h

@@ -25,4 +25,10 @@ namespace MobileGL::MG_Impl::GLImpl::FramebufferImpl {
     // not be multisampled. Incompleteness is INVALID_FRAMEBUFFER_OPERATION, the other two are
     // INVALID_OPERATION.
     Bool ValidateReadFramebufferForCopy(const char* caller);
+    // The pname sets of glGet/FramebufferParameteri (GL 4.6 core 9.2.3). Order matters and is part
+    // of the contract: a name outside the table is INVALID_ENUM, and only then is a name that the
+    // DEFAULT framebuffer does not answer INVALID_OPERATION. Testing the framebuffer kind first
+    // would turn GL_FRAMEBUFFER_DEFAULT_WIDTH on framebuffer zero into the wrong error.
+    Bool ValidateFramebufferParameterPname(GLenum pname, Bool isDefaultFramebuffer, Bool forSetter,
+                                           const char* caller);
 } // namespace MobileGL::MG_Impl::GLImpl::FramebufferImpl

MobileGL/MG_State/GLState/FramebufferState/FramebufferObject.cpp

@@ -185,6 +185,20 @@ namespace MobileGL::MG_State::GLState {
         return m_externalIndex;
     }
 
+#define MOBILEGL_DEFINE_FRAMEBUFFER_DEFAULT_SETTER(name, member, type)                                                \
+    void FramebufferObject::Set##name(type value) {                                                                    \
+        if (member == value) return;                                                                                    \
+        member = value;                                                                                                 \
+        ++m_objectVersion;                                                                                              \
+    }
+
+    MOBILEGL_DEFINE_FRAMEBUFFER_DEFAULT_SETTER(DefaultWidth, m_defaultWidth, Int)
+    MOBILEGL_DEFINE_FRAMEBUFFER_DEFAULT_SETTER(DefaultHeight, m_defaultHeight, Int)
+    MOBILEGL_DEFINE_FRAMEBUFFER_DEFAULT_SETTER(DefaultLayers, m_defaultLayers, Int)
+    MOBILEGL_DEFINE_FRAMEBUFFER_DEFAULT_SETTER(DefaultSamples, m_defaultSamples, Int)
+    MOBILEGL_DEFINE_FRAMEBUFFER_DEFAULT_SETTER(DefaultFixedSampleLocations, m_defaultFixedSampleLocations, Bool)
+#undef MOBILEGL_DEFINE_FRAMEBUFFER_DEFAULT_SETTER
+
     void FramebufferObject::BumpAttachmentVersion(FramebufferAttachmentType type) {
         ++m_attachmentVersions[static_cast<SizeT>(type)];
         ++m_objectVersion;

MobileGL/MG_State/GLState/FramebufferState/FramebufferObject.h

@@ -129,6 +129,19 @@ namespace MobileGL {
             void SetReadBuffer(FramebufferAttachmentType buf);
             FramebufferAttachmentType GetReadBuffer() const { return m_readBuffer; }
 
+            // GL_ARB_framebuffer_no_attachments state (GL 4.6 core table 23.24). The shape a
+            // framebuffer with no attachments would rasterize at; all zero / FALSE until set.
+            Int GetDefaultWidth() const { return m_defaultWidth; }
+            Int GetDefaultHeight() const { return m_defaultHeight; }
+            Int GetDefaultLayers() const { return m_defaultLayers; }
+            Int GetDefaultSamples() const { return m_defaultSamples; }
+            Bool GetDefaultFixedSampleLocations() const { return m_defaultFixedSampleLocations; }
+            void SetDefaultWidth(Int value);
+            void SetDefaultHeight(Int value);
+            void SetDefaultLayers(Int value);
+            void SetDefaultSamples(Int value);
+            void SetDefaultFixedSampleLocations(Bool value);
+
             FramebufferAttachmentVersionArray GetAllFramebufferAttachmentVersions() const {
                 return m_attachmentVersions;
             }
@@ -148,6 +161,12 @@ namespace MobileGL {
             FramebufferAttachmentArray m_drawBuffers; // Probably no versioning needed for this, just check equality
             FramebufferAttachmentType m_readBuffer = FramebufferAttachmentType::None;
 
+            Int m_defaultWidth = 0;
+            Int m_defaultHeight = 0;
+            Int m_defaultLayers = 0;
+            Int m_defaultSamples = 0;
+            Bool m_defaultFixedSampleLocations = false;
+
             // This version will bump when draw/read buffer changes (by `glDrawBuffer(s)`/`glReadBuffer`)
             Uint16 m_objectVersion = 0;
         };