tor-browser

commit 71b4f75f6415d7d2bff005540cef8061c42ad0fd
parent 73481247ed635fdcb224f73545b7aab034c69967
Author: Jamie Nicol <jnicol@mozilla.com>
Date:   Thu, 16 Oct 2025 12:25:00 +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
 | 
10
++++++++++
M
gfx/gl/GLContext.h
 | 
17
++++++++++++++++-

2 files changed, 26 insertions(+), 1 deletion(-)
diff --git a/gfx/gl/GLContext.cpp b/gfx/gl/GLContext.cpp
@@ -885,6 +885,7 @@ bool GLContext::InitImpl() {
   raw_fGetIntegerv(LOCAL_GL_MAX_CUBE_MAP_TEXTURE_SIZE, &mMaxCubeMapTextureSize);
   raw_fGetIntegerv(LOCAL_GL_MAX_RENDERBUFFER_SIZE, &mMaxRenderbufferSize);
   raw_fGetIntegerv(LOCAL_GL_MAX_VIEWPORT_DIMS, mMaxViewportDims);
+  raw_fGetIntegerv(LOCAL_GL_MAX_VERTEX_ATTRIB_STRIDE, &mMaxVertexAttribStride);
 
   if (mWorkAroundDriverBugs) {
     int maxTexSize = INT32_MAX;
@@ -942,6 +943,15 @@ 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.
+    mVertexBufferExtraPadding = Some(mMaxVertexAttribStride);
+  }
+#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) {
@@ -3909,10 +3920,14 @@ class GLContext : public GenericAtomicRefCounted, public SupportsWeakPtr {
   GLint mMaxCubeMapTextureSize = 0;
   GLint mMaxRenderbufferSize = 0;
   GLint mMaxViewportDims[2] = {};
+  GLint mMaxVertexAttribStride = 0;
   GLsizei mMaxSamples = 0;
   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;