WebGL 2: validate read buffer attachment when reading from FBO

Source/core/html/canvas/WebGLRenderingContextBase.cpp

Index: Source/core/html/canvas/WebGLRenderingContextBase.cpp
diff --git a/Source/core/html/canvas/WebGLRenderingContextBase.cpp b/Source/core/html/canvas/WebGLRenderingContextBase.cpp
index 66aca1a524d6d8ab7eacc656b8705ac81aeffb47..d98daa19d284afc00d0fa04d21121b39bbff92fb 100644
--- a/Source/core/html/canvas/WebGLRenderingContextBase.cpp
+++ b/Source/core/html/canvas/WebGLRenderingContextBase.cpp
@@ -1543,6 +1543,19 @@ bool WebGLRenderingContextBase::validateSettableTexFormat(const char* functionNa
     return true;
 }
 
+bool WebGLRenderingContextBase::validateReadBufferAttachment(const char* functionName, const WebGLFramebuffer* readFramebufferBinding)
+{
+    if (readFramebufferBinding) {
+        GLenum readBuffer = readFramebufferBinding->getReadBuffer();
+        WebGLSharedObject* attachmentObject = readFramebufferBinding->getAttachmentObject(readBuffer);
+        if (!attachmentObject) {
+            synthesizeGLError(GL_INVALID_OPERATION, functionName, "no image attached to read buffer");
+            return false;
+        }
+    }
+    return true;

[Zhenyao Mo, 2015/07/06 17:52:25]

Shouldn't you also check here that the back buffer's readbuffer is not NONE? in
which case, you should define m_readbuffer in this base class, and its value
will just stay GL_BACK in WebGL 1.

[Ken Russell (switch to Gerrit), 2015/07/06 21:19:13]

Agree with Mo's observation, though if the underlying GL implementation will
catch this (since the call to glReadBuffer(GL_NONE) will go through to the
driver), it's OK to not explicitly check it here.

I generally agree with Mo's observation to move m_readBuffer to the base class
and initialize it to GL_BACK. Also, I think should be renamed to something like
m_defaultFramebufferReadBuffer.

[yunchao, 2015/07/07 08:10:39]

Done.

+}
+
 void WebGLRenderingContextBase::copyTexImage2D(GLenum target, GLint level, GLenum internalformat, GLint x, GLint y, GLsizei width, GLsizei height, GLint border)
 {
     if (isContextLost())
@@ -1573,6 +1586,8 @@ void WebGLRenderingContextBase::copyTexImage2D(GLenum target, GLint level, GLenu
         synthesizeGLError(GL_INVALID_FRAMEBUFFER_OPERATION, "copyTexImage2D", reason);
         return;
     }
+    if (!validateReadBufferAttachment("copyTexImage2D", readFramebufferBinding))
+        return;
     clearIfComposited();
     ScopedDrawingBufferBinder binder(drawingBuffer(), readFramebufferBinding);
     webContext()->copyTexImage2D(target, level, internalformat, x, y, width, height, border);
@@ -1618,6 +1633,8 @@ void WebGLRenderingContextBase::copyTexSubImage2D(GLenum target, GLint level, GL
         synthesizeGLError(GL_INVALID_FRAMEBUFFER_OPERATION, "copyTexSubImage2D", reason);
         return;
     }
+    if (!validateReadBufferAttachment("copyTexSubImage2D", readFramebufferBinding))
+        return;
     clearIfComposited();
     ScopedDrawingBufferBinder binder(drawingBuffer(), readFramebufferBinding);
     webContext()->copyTexSubImage2D(target, level, xoffset, yoffset, x, y, width, height);
@@ -3359,6 +3376,9 @@ void WebGLRenderingContextBase::readPixels(GLint x, GLint y, GLsizei width, GLsi
         return;
     }
 
+    if (!validateReadBufferAttachment("readPixels", readFramebufferBinding))
+        return;
+
     clearIfComposited();
     void* data = pixels->baseAddress();