Backends: OpenGL: Partially revert 1.86 change of using glBufferSubData(): now only done on Intel GPUs. (#4468, #3381, #2981, #4825, #4832, #5127)

Essentially reverts 389982eb for non-Intel GPUs + update imgui_impl_opengl3_loader.h
Amended once (force-pushed).

backends/imgui_impl_opengl3.cpp

@@ -14,6 +14,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2022-05-23: OpenGL: Reworking 2021-12-15 "Using buffer orphaning" so it only happens on Intel GPU, seems to cause problems otherwise. (#4468, #4825, #4832, #5127).
 //  2022-05-13: OpenGL: Fix state corruption on OpenGL ES 2.0 due to not preserving GL_ELEMENT_ARRAY_BUFFER_BINDING and vertex attribute states.
 //  2021-12-15: OpenGL: Using buffer orphaning + glBufferSubData(), seems to fix leaks with multi-viewports with some Intel HD drivers.
 //  2021-08-23: OpenGL: Fixed ES 3.0 shader ("#version 300 es") use normal precision floats to avoid wobbly rendering at HD resolutions.
@@ -193,6 +194,7 @@ struct ImGui_ImplOpenGL3_Data
     GLsizeiptr      VertexBufferSize;
     GLsizeiptr      IndexBufferSize;
     bool            HasClipOrigin;
+    bool            UseBufferSubData;
 
     ImGui_ImplOpenGL3_Data() { memset((void*)this, 0, sizeof(*this)); }
 };
@@ -261,6 +263,14 @@ bool    ImGui_ImplOpenGL3_Init(const char* glsl_version)
         sscanf(gl_version, "%d.%d", &major, &minor);
     }
     bd->GlVersion = (GLuint)(major * 100 + minor * 10);
+
+    // Query vendor to enable glBufferSubData kludge
+#ifdef _WIN32
+    if (const char* vendor = (const char*)glGetString(GL_VENDOR))
+        if (strncmp(vendor, "Intel", 5) == 0)
+            bd->UseBufferSubData = true;
+#endif
+    //printf("GL_MAJOR_VERSION = %d\nGL_MINOR_VERSION = %d\nGL_VENDOR = '%s'\nGL_RENDERER = '%s'\n", major, minor, (const char*)glGetString(GL_VENDOR), (const char*)glGetString(GL_RENDERER)); // [DEBUG]
 #else
     bd->GlVersion = 200; // GLES 2
 #endif
@@ -474,8 +484,13 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
         const ImDrawList* cmd_list = draw_data->CmdLists[n];
 
         // Upload vertex/index buffers
-        GLsizeiptr vtx_buffer_size = (GLsizeiptr)cmd_list->VtxBuffer.Size * (int)sizeof(ImDrawVert);
+        // - On Intel windows drivers we got reports that regular glBufferData() led to accumulating leaks when using multi-viewports, so we started using orphaning + glBufferSubData(). (See https://github.com/ocornut/imgui/issues/4468)
-        GLsizeiptr idx_buffer_size = (GLsizeiptr)cmd_list->IdxBuffer.Size * (int)sizeof(ImDrawIdx);
+        // - On NVIDIA drivers we got reports that using orphaning + glBufferSubData() led to glitches when using multi-viewports.
+        // - OpenGL drivers are in a very sorry state in 2022, for now we are switching code path based on vendors.
+        const GLsizeiptr vtx_buffer_size = (GLsizeiptr)cmd_list->VtxBuffer.Size * (int)sizeof(ImDrawVert);
+        const GLsizeiptr idx_buffer_size = (GLsizeiptr)cmd_list->IdxBuffer.Size * (int)sizeof(ImDrawIdx);
+        if (bd->UseBufferSubData)
+        {
             if (bd->VertexBufferSize < vtx_buffer_size)
             {
                 bd->VertexBufferSize = vtx_buffer_size;
@@ -488,6 +503,12 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
             }
             glBufferSubData(GL_ARRAY_BUFFER, 0, vtx_buffer_size, (const GLvoid*)cmd_list->VtxBuffer.Data);
             glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, idx_buffer_size, (const GLvoid*)cmd_list->IdxBuffer.Data);
+        }
+        else
+        {
+            glBufferData(GL_ARRAY_BUFFER, vtx_buffer_size, (const GLvoid*)cmd_list->VtxBuffer.Data, GL_STREAM_DRAW);
+            glBufferData(GL_ELEMENT_ARRAY_BUFFER, idx_buffer_size, (const GLvoid*)cmd_list->IdxBuffer.Data, GL_STREAM_DRAW);
+        }
 
         for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.Size; cmd_i++)
         {

backends/imgui_impl_opengl3_loader.h

@@ -164,6 +164,8 @@ typedef khronos_uint8_t GLubyte;
 #define GL_FLOAT                          0x1406
 #define GL_RGBA                           0x1908
 #define GL_FILL                           0x1B02
+#define GL_VENDOR                         0x1F00
+#define GL_RENDERER                       0x1F01
 #define GL_VERSION                        0x1F02
 #define GL_EXTENSIONS                     0x1F03
 #define GL_LINEAR                         0x2601

docs/CHANGELOG.txt

@@ -121,6 +121,13 @@ Other Changes:
 - Backends: OSX: Monitor NSKeyUp events to catch missing keyUp for key when user press Cmd + key (#5128) [@thedmd]
 - Backends: OSX, Metal: Store backend data in a per-context struct, allowing to use these backends with
   multiple contexts. (#5203, #5221, #4141) [@noisewuwei]
+- Backends: OpenGL3: Partially revert 1.86 change of using glBufferSubData(): now only done on Windows and
+  Intel GPU, based on querying glGetString(GL_VENDOR). Essentially we got report of accumulating leaks on Intel
+  with multi-viewports when using simple glBufferData() without orphaning, and report of corruptions on other
+  GPUs with multi-viewports when using orphaning and glBufferSubData(), so currently switching technique based
+  on GPU vendor, which unfortunately reinforce the cargo-cult nature of dealing with OpenGL drivers.
+  Navigating the space of mysterious OpenGL drivers is particularly difficult as they are known to rely on
+  application specific whitelisting. (#4468, #3381, #2981, #4825, #4832, #5127).
 - Backends: OpenGL3: Fix state corruption on OpenGL ES 2.0 due to not preserving GL_ELEMENT_ARRAY_BUFFER_BINDING
   and vertex attribute states. [@rokups]
 - Examples: Emscripten+WebGPU: Fix building for latest WebGPU specs. (#3632)