[Fix] (MG_Impl): let a buffer clear name any format the spec allows

glClearBufferData and friends accepted exactly two argument triples - R8UI with
UNSIGNED_BYTE and R32UI with UNSIGNED_INT, both through RED_INTEGER - and raised
INVALID_ENUM for everything else. That is most of the entry point missing rather than a
narrow gap: GL takes any of the sized formats in the buffer-texture table, which is what an
application clearing an RGBA8 or R32F buffer uses.

The wrong error also hid the checks behind it. A test clearing a mapped buffer, or one
passing a misaligned offset, never reached those rules because the format tuple was rejected
first, so INVALID_ENUM came back where INVALID_OPERATION or INVALID_VALUE was due - the
validation was there and correct all along, just unreachable.

internalformat now goes through the same table the buffer textures use (shared rather than
written out twice, since it is the same list for the same reason), and format and type
through the ordinary pixel format converters. The element size comes from the internal
format, which is what offset and size have to be multiples of. Note that a bad format or
type here is INVALID_VALUE, not INVALID_ENUM (GL 4.6 core 6.3) - the odd one out among the
enum arguments, and what the conformance tests check for.

The pattern is still replicated verbatim, which is correct while the client layout matches
the internal format - every real caller, and every conformance case. When they differ it now
says so instead of quietly writing a differently-sized pattern.

direct_state_access.buffers_clear and buffers_functional pass on both backends;
buffers_errors is down to one unrelated complaint about glMapNamedBufferRange.

MobileGL/MG_Impl/GLImpl/Buffer/GL_Buffer.cpp

@@ -8,6 +8,9 @@
 
 #include "GL_Buffer.h"
 #include "Validators.h"
+#include "../Texture/GL_Texture.h"
+#include <MG_Util/Converters/GLToMG/TextureEnumConverter.h>
+#include <MG_Util/Metrics/TextureMetrics.h>
 #include <Config.h>
 #include <MG_State/GLState/Core.h>
 #include <MG_State/GLState/ErrorState/Error.h>
@@ -92,25 +95,64 @@ namespace MobileGL::MG_Impl::GLImpl {
 
         SharedPtr<MG_State::GLState::BufferObject> GetNamedBufferObject(GLuint buffer, BufferOp op);
 
+        // The size of one cleared element, which is what offset and size must be multiples of
+        // (GL 4.6 core 6.3). `internalformat` is restricted to the buffer-texture format table, and
+        // `format`/`type` describe the client-side pattern, so both are validated here and the
+        // caller only has to know how wide an element is.
         SizeT GetClearPatternSize(GLenum internalformat, GLenum format, GLenum type, BufferOp op) {
-            if (format != GL_RED_INTEGER) {
+            if (!IsBufferTextureInternalFormat(internalformat)) {
                 MG_State::pGLContext->RecordError(
                     ErrorCode::InvalidEnum,
-                    MakeUnique<GenericErrorInfo>("MG_Impl/GLImpl", GetBufferOpName(op),
-                                                 "Only GL_RED_INTEGER buffer clears are currently supported."));
+                    MakeUnique<GenericErrorInfo>(
+                        "MG_Impl/GLImpl", GetBufferOpName(op),
+                        std::format("internalformat 0x{:X} is not one of the sized formats a buffer clear accepts.",
+                                    internalformat)));
                 return 0;
             }
 
-            if (internalformat == GL_R8UI && type == GL_UNSIGNED_BYTE) return sizeof(GLubyte);
-            if (internalformat == GL_R32UI && type == GL_UNSIGNED_INT) return sizeof(GLuint);
+            // Unlike internalformat, a bad format or type here is INVALID_VALUE rather than
+            // INVALID_ENUM (GL 4.6 core 6.3) - the odd one out among the enum arguments.
+            const TextureInputFormat inputFormat = MG_Util::ConvertGLEnumToTextureInputFormat(format);
+            if (inputFormat == TextureInputFormat::Unknown) {
+                MG_State::pGLContext->RecordError(
+                    ErrorCode::InvalidValue,
+                    MakeUnique<GenericErrorInfo>("MG_Impl/GLImpl", GetBufferOpName(op),
+                                                 std::format("format 0x{:X} is not a pixel format.", format)));
+                return 0;
+            }
 
-            MG_State::pGLContext->RecordError(
-                ErrorCode::InvalidEnum,
-                MakeUnique<GenericErrorInfo>("MG_Impl/GLImpl", GetBufferOpName(op),
-                                             std::format("Unsupported clear format tuple: internalformat=0x{:X}, "
-                                                         "format=0x{:X}, type=0x{:X}",
-                                                         internalformat, format, type)));
-            return 0;
+            const TexturePixelDataType pixelType = MG_Util::ConvertGLEnumToTexturePixelDataType(type);
+            if (pixelType == TexturePixelDataType::Unknown) {
+                MG_State::pGLContext->RecordError(
+                    ErrorCode::InvalidValue,
+                    MakeUnique<GenericErrorInfo>("MG_Impl/GLImpl", GetBufferOpName(op),
+                                                 std::format("type 0x{:X} is not a pixel type.", type)));
+                return 0;
+            }
+
+            const TextureInternalFormat internal =
+                MG_Util::ConvertGLEnumToTextureInternalFormat(internalformat);
+            const SizeT elementSize = MG_Util::GetSizedInternalFormatSizeInBytes(internal);
+            if (elementSize == 0) {
+                MG_State::pGLContext->RecordError(
+                    ErrorCode::InvalidEnum,
+                    MakeUnique<GenericErrorInfo>("MG_Impl/GLImpl", GetBufferOpName(op),
+                                                 std::format("internalformat 0x{:X} has no known element size.",
+                                                             internalformat)));
+                return 0;
+            }
+
+            // The pattern is replicated verbatim, which is only the whole story while the client
+            // layout already matches the internal format - the case every entry point in practice
+            // uses, and the only one the conversion machinery here can express. Say so rather than
+            // quietly writing a differently-sized pattern.
+            const SizeT sourceSize = MG_Util::GetInputBytesPerPixel(inputFormat, pixelType);
+            if (sourceSize != elementSize) {
+                MGLOG_W("%s: clear pattern is %zu bytes but internalformat 0x%X stores %zu; "
+                        "converting between them is not implemented",
+                        GetBufferOpName(op), sourceSize, internalformat, elementSize);
+            }
+            return elementSize;
         }
 
         Bool ValidateBufferClearRange(const SharedPtr<MG_State::GLState::BufferObject>& bufferObject, GLintptr offset,

MobileGL/MG_Impl/GLImpl/Texture/GL_Texture.cpp

@@ -2072,7 +2072,7 @@ namespace MobileGL::MG_Impl::GLImpl {
     // than freezing the size it happens to have now.
     // The sized internal formats a buffer texture accepts (GL 4.6 core table 8.16). This is a much
     // shorter list than the renderable or texturable formats, so it cannot be inferred from either.
-    static Bool IsBufferTextureInternalFormat(GLenum internalformat) {
+    Bool IsBufferTextureInternalFormat(GLenum internalformat) {
         switch (internalformat) {
         case GL_R8:
         case GL_R16:

MobileGL/MG_Impl/GLImpl/Texture/GL_Texture.h

@@ -11,6 +11,10 @@
 
 namespace MobileGL::MG_Impl::GLImpl {
     /* @INSERTION_POINT:FUNCTION_DECLARATION@ */
+    // The sized internal formats a buffer texture accepts (GL 4.6 core table 8.16). The buffer
+    // clears take the same list, so it is shared rather than written out twice.
+    Bool IsBufferTextureInternalFormat(GLenum internalformat);
+
     void ClearTexImage(GLuint texture, GLint level, GLenum format, GLenum type, const void* data);
     void ClearTexSubImage(GLuint texture, GLint level, GLint xoffset, GLint yoffset, GLint zoffset, GLsizei width,
                           GLsizei height, GLsizei depth, GLenum format, GLenum type, const void* data);