Bug 1321129 - make nsShmImage stride compatible with XShm. r=karlt

MozReview-Commit-ID: GuiVTPKvAZM

config/system-headers

@@ -1231,6 +1231,7 @@ X11/extensions/Xrender.h
 X11/extensions/Xfixes.h
 X11/extensions/Xdamage.h
 X11/extensions/Xcomposite.h
+X11/ImUtil.h
 X11/Intrinsic.h
 X11/keysymdef.h
 X11/keysym.h

widget/nsShmImage.cpp

@@ -19,6 +19,10 @@
 #include <sys/ipc.h>
 #include <sys/shm.h>
 
+extern "C" {
+#include <X11/ImUtil.h>
+}
+
 using namespace mozilla::ipc;
 using namespace mozilla::gfx;
 
@@ -26,11 +30,14 @@ nsShmImage::nsShmImage(Display* aDisplay,
                        Drawable aWindow,
                        Visual* aVisual,
                        unsigned int aDepth)
-  : mWindow(aWindow)
+  : mDisplay(aDisplay)
+  , mConnection(XGetXCBConnection(aDisplay))
+  , mWindow(aWindow)
   , mVisual(aVisual)
   , mDepth(aDepth)
   , mFormat(mozilla::gfx::SurfaceFormat::UNKNOWN)
   , mSize(0, 0)
+  , mStride(0)
   , mPixmap(XCB_NONE)
   , mGC(XCB_NONE)
   , mRequestPending(false)
@@ -38,7 +45,6 @@ nsShmImage::nsShmImage(Display* aDisplay,
   , mShmId(-1)
   , mShmAddr(nullptr)
 {
-  mConnection = XGetXCBConnection(aDisplay);
   mozilla::PodZero(&mSyncRequest);
 }
 
@@ -58,8 +64,7 @@ bool nsShmImage::UseShm()
 bool
 nsShmImage::CreateShmSegment()
 {
-  size_t size = SharedMemory::PageAlignedSize(BytesPerPixel(mFormat) *
-                                              mSize.width * mSize.height);
+  size_t size = SharedMemory::PageAlignedSize(mStride * mSize.height);
 
   mShmId = shmget(IPC_PRIVATE, size, IPC_CREAT | 0600);
   if (mShmId == -1) {
@@ -187,6 +192,13 @@ nsShmImage::CreateImage(const IntSize& aSize)
     return false;
   }
 
+  // Round up stride to the display's scanline pad (in bits) as XShm expects.
+  int scanlinePad = _XGetScanlinePad(mDisplay, mDepth);
+  int bitsPerPixel = _XGetBitsPerPixel(mDisplay, mDepth);
+  int bitsPerLine = ((bitsPerPixel * aSize.width + scanlinePad - 1)
+                     / scanlinePad) * scanlinePad;
+  mStride = bitsPerLine / 8;
+
   if (!CreateShmSegment()) {
     DestroyImage();
     return false;
@@ -277,9 +289,9 @@ nsShmImage::CreateDrawTarget(const mozilla::LayoutDeviceIntRegion& aRegion)
 
   return gfxPlatform::CreateDrawTargetForData(
     reinterpret_cast<unsigned char*>(mShmAddr)
-      + BytesPerPixel(mFormat) * (bounds.y * mSize.width + bounds.x),
+      + bounds.y * mStride + bounds.x * BytesPerPixel(mFormat),
     bounds.Size(),
-    BytesPerPixel(mFormat) * mSize.width,
+    mStride,
     mFormat);
 }
 

widget/nsShmImage.h

@@ -50,6 +50,7 @@ private:
 
   void WaitIfPendingReply();
 
+  Display*                     mDisplay;
   xcb_connection_t*            mConnection;
   Window                       mWindow;
   Visual*                      mVisual;
@@ -57,6 +58,7 @@ private:
 
   mozilla::gfx::SurfaceFormat  mFormat;
   mozilla::gfx::IntSize        mSize;
+  int                          mStride;
 
   xcb_pixmap_t                 mPixmap;
   xcb_gcontext_t               mGC;