[Feat] (MG_Impl, MG_State, MG_Util): attach a buffer texture to a range of its buffer

glTexBufferRange, glTextureBuffer and glTextureBufferRange were all stubs, so a
buffer texture could only ever be attached through glTexBuffer -- by binding, and
always to the whole buffer.

Give the buffer texture the window it is supposed to address. The non-range forms
record it as offset 0 with a whole-buffer sentinel rather than the size the buffer
happens to have, so a later respecify keeps being followed instead of freezing the
texture at yesterday's size. All four entry points now share one attach path,
differing only in how they name the texture: by binding for the target forms, by
name for the DSA ones.

Both backends honour the window: DirectVulkan offsets and clamps the buffer view,
DirectGLES uses glTexBufferRange when the texture names a sub-range and keeps
plain glTexBuffer for the whole-buffer case, which also works on a driver without
the range entry point.

GL_TEXTURE_BUFFER_OFFSET_ALIGNMENT reported 0 with a comment explaining that the
range entry points were stubbed. It now reports what the device actually requires
-- minTexelBufferOffsetAlignment on Vulkan, the driver's own value on GLES -- and
the range entry points enforce it. Zero was never a legal answer; the minimum is
1, and an application that trusted it would have built unaligned offsets.

MobileGL/MG_Backend/BackendObject.h

@@ -315,6 +315,8 @@ namespace MobileGL {
             Int MaxComputeWorkGroupInvocations = 128;
             Int MaxShaderStorageBufferBindings = 8;
             Int MaxTextureBufferSize = 65536;
+            // GL_TEXTURE_BUFFER_OFFSET_ALIGNMENT; 1 means the offset is unconstrained.
+            Int TextureBufferOffsetAlignment = 1;
             Int MaxUniformBufferBindings = 24;
             Int MaxUniformBlockSize = 16384;
             Int MaxImageUnits = 8;

MobileGL/MG_Backend/DirectGLES/BackendObject_DirectGLES.cpp

@@ -1112,6 +1112,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
         m_dynamicParameters.MaxComputeWorkGroupInvocations = m_GLESCapabilities.MaxComputeWorkGroupInvocations;
         m_dynamicParameters.MaxShaderStorageBufferBindings = m_GLESCapabilities.MaxShaderStorageBufferBindings;
         m_dynamicParameters.MaxTextureBufferSize = m_GLESCapabilities.MaxTextureBufferSize;
+        m_dynamicParameters.TextureBufferOffsetAlignment = m_GLESCapabilities.TextureBufferOffsetAlignment;
         m_dynamicParameters.MaxUniformBufferBindings = m_GLESCapabilities.MaxUniformBufferBindings;
         m_dynamicParameters.MaxUniformBlockSize = m_GLESCapabilities.MaxUniformBlockSize;
         const Int maxSupportedTextureUnits =

MobileGL/MG_Backend/DirectGLES/Managers.cpp

@@ -2232,7 +2232,24 @@ namespace MobileGL::MG_Backend::DirectGLES {
                             "ID: %u, buffer ID: %u, buffer size: %zu, format: %s",
                             m_backendTextureId, backendId, buffer->GetSize(),
                             MG_Util::ConvertGLEnumToString(glInternalFormat).c_str());
-                    g_GLESFuncs.glTexBuffer(GL_TEXTURE_BUFFER, glInternalFormat, backendId);
+                    // A texture that names a window of the buffer needs the range form; the
+                    // whole-buffer forms report offset 0 and the buffer's current size, which
+                    // glTexBuffer expresses more directly (and works where the range entry point
+                    // is absent).
+                    const SizeT rangeOffset = textureBufferObject->GetBufferRangeOffset();
+                    const SizeT rangeSize = textureBufferObject->GetBufferRangeSizeInBytes();
+                    if (rangeOffset == 0 && rangeSize == buffer->GetSize()) {
+                        g_GLESFuncs.glTexBuffer(GL_TEXTURE_BUFFER, glInternalFormat, backendId);
+                    } else if (g_GLESFuncs.glTexBufferRange != nullptr) {
+                        g_GLESFuncs.glTexBufferRange(GL_TEXTURE_BUFFER, glInternalFormat, backendId,
+                                                     static_cast<GLintptr>(rangeOffset),
+                                                     static_cast<GLsizeiptr>(rangeSize));
+                    } else {
+                        MGLOG_E("Texture buffer %u names a sub-range but the driver has no "
+                                "glTexBufferRange; binding the whole buffer instead",
+                                stateTextureObject->GetExternalIndex());
+                        g_GLESFuncs.glTexBuffer(GL_TEXTURE_BUFFER, glInternalFormat, backendId);
+                    }
                     DebugImpl::ErrorLopper::Loop(
                         [file = __FILE__, line = __LINE__, func = __func__, glInternalFormat, backendId](GLenum err) {
                             MGLOG_D("%s(%s:%d) glTexBuffer(format=%s, buffer=%u) ES error: %s",

MobileGL/MG_Backend/DirectVulkan/BackendObject_DirectVulkan.cpp

@@ -780,6 +780,7 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         m_dynamicParameters.MaxComputeWorkGroupInvocations = m_vulkanCaps.MaxComputeWorkGroupInvocations;
         m_dynamicParameters.MaxShaderStorageBufferBindings = m_vulkanCaps.MaxShaderStorageBufferBindings;
         m_dynamicParameters.MaxTextureBufferSize = m_vulkanCaps.MaxTextureBufferSize;
+        m_dynamicParameters.TextureBufferOffsetAlignment = m_vulkanCaps.TextureBufferOffsetAlignment;
         m_dynamicParameters.MaxUniformBufferBindings = m_vulkanCaps.MaxUniformBufferBindings;
         m_dynamicParameters.MaxUniformBlockSize = m_vulkanCaps.MaxUniformBlockSize;
         m_dynamicParameters.MaxImageUnits =

MobileGL/MG_Backend/DirectVulkan/Renderer/UniformManager.cpp

@@ -600,7 +600,11 @@ namespace MobileGL::MG_Backend::DirectVulkan {
 
         const VkDeviceSize texelSize =
             static_cast<VkDeviceSize>(MG_Util::GetSizedInternalFormatSizeInBytes(internalFormat));
-        VkDeviceSize viewRange = slice.size;
+        // glTextureBufferRange addresses a window of the buffer, not all of it; the whole-buffer
+        // forms report the buffer's current size here, so both go through the same clamp.
+        const VkDeviceSize rangeOffset = static_cast<VkDeviceSize>(textureBuffer->GetBufferRangeOffset());
+        const VkDeviceSize rangeSize = static_cast<VkDeviceSize>(textureBuffer->GetBufferRangeSizeInBytes());
+        VkDeviceSize viewRange = std::min(rangeSize, slice.size > rangeOffset ? slice.size - rangeOffset : 0);
         if (texelSize > 0) {
             viewRange = (viewRange / texelSize) * texelSize;
         }
@@ -613,7 +617,7 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         viewInfo.sType = VK_STRUCTURE_TYPE_BUFFER_VIEW_CREATE_INFO;
         viewInfo.buffer = slice.buffer;
         viewInfo.format = vkFormat;
-        viewInfo.offset = slice.offset;
+        viewInfo.offset = slice.offset + rangeOffset;
         viewInfo.range = viewRange;
 
         VkBufferView bufferView = VK_NULL_HANDLE;