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

Source/modules/webgl/WebGLRenderingContextBase.cpp

Index: Source/modules/webgl/WebGLRenderingContextBase.cpp
diff --git a/Source/modules/webgl/WebGLRenderingContextBase.cpp b/Source/modules/webgl/WebGLRenderingContextBase.cpp
index 53aaea0151620316a369e2c80916623f0b6df6ab..e7ae2706065aa6304a0e718e6597a6d1cdcdab62 100644
--- a/Source/modules/webgl/WebGLRenderingContextBase.cpp
+++ b/Source/modules/webgl/WebGLRenderingContextBase.cpp
@@ -967,6 +967,7 @@ void WebGLRenderingContextBase::initializeNewContext()
     m_unpackPremultiplyAlpha = false;
     m_unpackColorspaceConversion = GC3D_BROWSER_DEFAULT_WEBGL;
     m_boundArrayBuffer = nullptr;
+    m_boundPixelPackBuffer = nullptr;
     m_currentProgram = nullptr;
     m_framebufferBinding = nullptr;
     m_renderbufferBinding = nullptr;
@@ -1098,6 +1099,7 @@ WebGLRenderingContextBase::~WebGLRenderingContextBase()
     // Remove all references to WebGLObjects so if they are the last reference
     // they will be freed before the last context is removed from the context group.
     m_boundArrayBuffer = nullptr;
+    m_boundPixelPackBuffer = nullptr;
     m_defaultVertexArrayObject = nullptr;
     m_boundVertexArrayObject = nullptr;
     m_vertexAttrib0Buffer = nullptr;
@@ -3729,6 +3731,31 @@ DOMArrayBufferView::ViewType WebGLRenderingContextBase::readPixelsExpectedArrayB
     }
 }
 
+bool WebGLRenderingContextBase::validateReadPixelsFuncParameters(GLsizei width, GLsizei height, GLenum format, GLenum type, unsigned domArrayBufferLength, WebGLFramebuffer*& readFramebufferBinding)
+{
+    if (!validateReadPixelsFormatAndType(format, type))
+        return false;
+    GLenum readBufferInternalFormat = 0, readBufferType = 0;
+    if (!validateReadBufferAndGetInfo("readPixels", readFramebufferBinding, &readBufferInternalFormat, &readBufferType))
+        return false;
+    if (!validateReadPixelsFormatTypeCombination(format, type, readBufferInternalFormat, readBufferType))
+        return false;
+
+    // Calculate array size, taking into consideration of PACK_ALIGNMENT.
+    unsigned totalBytesRequired = 0;
+    unsigned padding = 0;
+    GLenum error = WebGLImageConversion::computeImageSizeInBytes(format, type, width, height, m_packAlignment, &totalBytesRequired, &padding);
+    if (error != GL_NO_ERROR) {
+        synthesizeGLError(error, "readPixels", "invalid dimensions");
+        return false;
+    }
+    if (domArrayBufferLength && domArrayBufferLength < totalBytesRequired) {
+        synthesizeGLError(GL_INVALID_OPERATION, "readPixels", "ArrayBufferView not large enough for dimensions");
+        return false;
+    }
+    return true;
+}
+
 void WebGLRenderingContextBase::readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, DOMArrayBufferView* pixels)
 {
     if (isContextLost())
@@ -3736,19 +3763,15 @@ void WebGLRenderingContextBase::readPixels(GLint x, GLint y, GLsizei width, GLsi
     // Due to WebGL's same-origin restrictions, it is not possible to
     // taint the origin using the WebGL API.
     ASSERT(canvas()->originClean());
+    if (isWebGL2OrHigher() && m_boundPixelPackBuffer.get()) {
+        synthesizeGLError(GL_INVALID_OPERATION, "readPixels", "PIXEL_PACK buffer should not bound");
+        return;
+    }
     // Validate input parameters.
     if (!pixels) {
         synthesizeGLError(GL_INVALID_VALUE, "readPixels", "no destination ArrayBufferView");
         return;
     }
-    if (!validateReadPixelsFormatAndType(format, type))
-        return;
-    GLenum readBufferInternalFormat = 0, readBufferType = 0;
-    WebGLFramebuffer* readFramebufferBinding = nullptr;
-    if (!validateReadBufferAndGetInfo("readPixels", readFramebufferBinding, &readBufferInternalFormat, &readBufferType))
-        return;
-    if (!validateReadPixelsFormatTypeCombination(format, type, readBufferInternalFormat, readBufferType))
-        return;
 
     DOMArrayBufferView::ViewType expectedViewType = readPixelsExpectedArrayBufferViewType(type);
     // Validate array type against pixel type.
@@ -3757,18 +3780,9 @@ void WebGLRenderingContextBase::readPixels(GLint x, GLint y, GLsizei width, GLsi
         return;
     }
 
-    // Calculate array size, taking into consideration of PACK_ALIGNMENT.
-    unsigned totalBytesRequired = 0;
-    unsigned padding = 0;
-    GLenum error = WebGLImageConversion::computeImageSizeInBytes(format, type, width, height, m_packAlignment, &totalBytesRequired, &padding);
-    if (error != GL_NO_ERROR) {
-        synthesizeGLError(error, "readPixels", "invalid dimensions");
-        return;
-    }
-    if (pixels->byteLength() < totalBytesRequired) {
-        synthesizeGLError(GL_INVALID_OPERATION, "readPixels", "ArrayBufferView not large enough for dimensions");
+    WebGLFramebuffer* readFramebufferBinding = nullptr;
+    if (!validateReadPixelsFuncParameters(format, type, width, height, pixels->byteLength(), readFramebufferBinding))
         return;
-    }
 
     clearIfComposited();
     void* data = pixels->baseAddress();
@@ -3779,6 +3793,29 @@ void WebGLRenderingContextBase::readPixels(GLint x, GLint y, GLsizei width, GLsi
     }
 }
 
+void WebGLRenderingContextBase::readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, long long offset)
+{
+    if (isContextLost() || !isWebGL2OrHigher())
+        return;
+    // Due to WebGL's same-origin restrictions, it is not possible to
+    // taint the origin using the WebGL API.
+    ASSERT(canvas()->originClean());
+    if (!m_boundPixelPackBuffer.get()) {
+        synthesizeGLError(GL_INVALID_OPERATION, "readPixels", "no PIXEL_PACK buffer bound");
+        return;
+    }
+
+    WebGLFramebuffer* readFramebufferBinding = nullptr;
+    if (!validateReadPixelsFuncParameters(format, type, width, height, 0, readFramebufferBinding))
+        return;
+
+    clearIfComposited();
+    {
+        ScopedDrawingBufferBinder binder(drawingBuffer(), readFramebufferBinding);
+        webContext()->readPixels(x, y, width, height, format, type, (void*)offset);
+    }
+}
+
 void WebGLRenderingContextBase::renderbufferStorageImpl(
     GLenum target, GLsizei samples, GLenum internalformat, GLsizei width, GLsizei height,
     const char* functionName)
@@ -6588,6 +6625,7 @@ DEFINE_TRACE(WebGLRenderingContextBase)
     visitor->trace(m_contextLostCallbackAdapter);
     visitor->trace(m_errorMessageCallbackAdapter);
     visitor->trace(m_boundArrayBuffer);
+    visitor->trace(m_boundPixelPackBuffer);
     visitor->trace(m_defaultVertexArrayObject);
     visitor->trace(m_boundVertexArrayObject);
     visitor->trace(m_vertexAttrib0Buffer);