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 672270918c6d75a9ccdd2152dd3c76bb7ab830f9..dd74e171b0cd0713d7c26d000ad37b7a0c1b85f0 100644
--- a/Source/modules/webgl/WebGL2RenderingContextBase.cpp
+++ b/Source/modules/webgl/WebGL2RenderingContextBase.cpp
@@ -244,6 +244,42 @@ 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 be 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 (!validateValueFitNonNegInt32("readPixels", "offset", offset))
+        return;
+
+    WebGLBuffer* buffer = m_boundPixelPackBuffer.get();
+    if (!buffer) {
+        synthesizeGLError(GL_INVALID_OPERATION, "readPixels", "no PIXEL_PACK buffer bound");
+        return;
+    }
+
+    // Need to validate whether the pixel pack buffer is mapped,
+    // if we decide to expose mapBufferRange() to web developers.
+
+    long long size = buffer->getSize() - offset;
+
+    // If size is negative, or size is not large enough to store pixels,
+    // those cases are handled by readPixelsImpl to generate INVALID_OPERATION.
+    WebGLRenderingContextBase::readPixelsImpl(x, y, width, height, format, type, reinterpret_cast<void*>(offset), size);
+}
+
 void WebGL2RenderingContextBase::renderbufferStorageImpl(
     GLenum target, GLsizei samples, GLenum internalformat, GLsizei width, GLsizei height,
     const char* functionName)