tor-browser

commit 47a1818c6a30cb6192b2289993cf63c9bb419df7
parent eaa05d03ac167c6364984d22318fb4afe1c0c5d3
Author: Jamie Nicol <jnicol@mozilla.com>
Date:   Thu, 16 Oct 2025 16:04:02 +0000

Bug 1983036 - Pad vertex buffers with space for an extra vertex on Xclipse GPUs. r=gfx-reviewers,nical

On devices with Samsung Xclipse GPUs running Android 15, we see broken
rendering due to attribute data residing at the end of a vertex buffer
not being read correctly. Ensuring we pad the size of vertex buffers
by an additional GL_MAX_VERTEX_ATTRIB_STRIDE bytes (i.e. definitely
enough space for one additional vertex) avoids the issue.

Differential Revision: https://phabricator.services.mozilla.com/D268727

Diffstat:
M
gfx/gl/GLContext.cpp
 | 
11
+++++++++++
M
gfx/gl/GLContext.h
 | 
16
+++++++++++++++-

2 files changed, 26 insertions(+), 1 deletion(-)
diff --git a/gfx/gl/GLContext.cpp b/gfx/gl/GLContext.cpp
@@ -942,6 +942,17 @@ bool GLContext::InitImpl() {
 
   mMaxTexOrRbSize = std::min(mMaxTextureSize, mMaxRenderbufferSize);
 
+#ifdef MOZ_WIDGET_ANDROID
+  if (Renderer() == GLRenderer::SamsungXclipse && jni::GetAPIVersion() == 35) {
+    // On Samsung Xclipse GPUs on Android 15 attribute values for the final
+    // vertex in a buffer may be incorrect. Padding the buffer to contain
+    // enough space for an additional vertex avoids the issue. See bug 1983036.
+    GLint maxVertexAttribStride;
+    raw_fGetIntegerv(LOCAL_GL_MAX_VERTEX_ATTRIB_STRIDE, &maxVertexAttribStride);
+    mVertexBufferExtraPadding = Some(maxVertexAttribStride);
+  }
+#endif
+
   ////////////////////////////////////////////////////////////////////////////
 
   // We're ready for final setup.
diff --git a/gfx/gl/GLContext.h b/gfx/gl/GLContext.h
@@ -899,7 +899,18 @@ class GLContext : public GenericAtomicRefCounted, public SupportsWeakPtr {
  public:
   void fBufferData(GLenum target, GLsizeiptr size, const GLvoid* data,
                    GLenum usage) {
-    raw_fBufferData(target, size, data, usage);
+    if (WorkAroundDriverBugs() && target == LOCAL_GL_ARRAY_BUFFER &&
+        mVertexBufferExtraPadding) {
+      // Some drivers require extra padding at the end of array buffers.
+      // See bug 1983036.
+      raw_fBufferData(target, size + *mVertexBufferExtraPadding, nullptr,
+                      usage);
+      if (data) {
+        fBufferSubData(target, 0, size, data);
+      }
+    } else {
+      raw_fBufferData(target, size, data, usage);
+    }
 
     // bug 744888
     if (WorkAroundDriverBugs() && !data && Vendor() == GLVendor::NVIDIA) {
@@ -3913,6 +3924,9 @@ class GLContext : public GenericAtomicRefCounted, public SupportsWeakPtr {
   bool mNeedsTextureSizeChecks = false;
   bool mNeedsFlushBeforeDeleteFB = false;
   bool mTextureAllocCrashesOnMapFailure = false;
+  // Amount of additional padding bytes that must be allocated for
+  // GL_ARRAY_BUFFER buffers to work around driver bugs. See bug 1983036.
+  Maybe<GLint> mVertexBufferExtraPadding;
   const bool mWorkAroundDriverBugs;
   mutable uint64_t mSyncGLCallCount = 0;