WebGL 2: add readPixels API to read pixels into pixel pack buffer

Source/modules/webgl/WebGL2RenderingContextBase.cpp

Index: Source/modules/webgl/WebGL2RenderingContextBase.cpp
diff --git a/Source/modules/webgl/WebGL2RenderingContextBase.cpp b/Source/modules/webgl/WebGL2RenderingContextBase.cpp
index 8c61c89da95560926cbff64fb2e0759630ec2f9e..6fe323c14f60778d968173c99645e8c431253f17 100644
--- a/Source/modules/webgl/WebGL2RenderingContextBase.cpp
+++ b/Source/modules/webgl/WebGL2RenderingContextBase.cpp
@@ -244,6 +244,30 @@ void WebGL2RenderingContextBase::readBuffer(GLenum mode)
     webContext()->readBuffer(mode);
 }
 
+void WebGL2RenderingContextBase::readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, DOMArrayBufferView* pixels)
+{
+    if (isContextLost())
+        return;
+    if (m_boundPixelPackBuffer.get()) {
+        synthesizeGLError(GL_INVALID_OPERATION, "readPixels", "PIXEL_PACK buffer should not bound");
+        return;
+    }
+
+    WebGLRenderingContextBase::readPixels(x, y, width, height, format, type, pixels);
+}
+
+void WebGL2RenderingContextBase::readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, long long offset)
+{
+    if (isContextLost())
+        return;
+    if (!m_boundPixelPackBuffer.get()) {
+        synthesizeGLError(GL_INVALID_OPERATION, "readPixels", "no PIXEL_PACK buffer bound");
+        return;
+    }
+

[Zhenyao Mo, 2015/08/18 21:48:39]

There are some missing validations here.  I think you need to expand the
WebGLBuffer class to cache buffer size (from bufferData() call). We don't have
to validate if the buffer is mapped, since we decided not to expose
mapBuffferRange() function in WebGL 2 (probably add a comment in case that
decision gets revisited in the future), but we do need to validate if the buffer
size is large enough.  You need to validate of offset is within buffer range,
and then pass buffer size minus offset as the last arg to readPixelImpl(), it
gets validated.

[yunchao, 2015/08/19 09:33:39]

Yeah, I have written the code to validate the buffer access is within the buffer
range. The spec also have related statement. but when I looked into
bufferSubData, getBufferSubData and so forth, I found that they doesn't check
this. I should obey to the WebGL spec, not to the 
code in Blink.

It is done now.

I will update the other functions later.

+    WebGLRenderingContextBase::readPixelsImpl(x, y, width, height, format, type, (void*)offset, 0);

[Zhenyao Mo, 2015/08/18 21:48:39]

use static_cast instead of (void*).

[yunchao, 2015/08/19 09:33:39]

Thanks! I tried static_cast, but it failed to build. So I used reinterpret_cast
instead.

+}
+
 void WebGL2RenderingContextBase::renderbufferStorageImpl(
     GLenum target, GLsizei samples, GLenum internalformat, GLsizei width, GLsizei height,
     const char* functionName)