Add support for converting Colors to linear RGB; Fix relevant filters

Source/platform/graphics/ColorSpace.cpp

+/*
+ * Copyright (c) 2008, Google Inc. All rights reserved.
+ * Copyright (C) 2009 Dirk Schulze <krit@webkit.org>
+ * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "platform/graphics/ColorSpace.h"
+
+#include "wtf/MathExtras.h"
+#include "wtf/Vector.h"
+
+namespace WebCore {
+
+namespace ColorSpaceUtilities {
+
+namespace {
+
+const Vector<uint8_t>& getLinearRgbLUT()
+{
+    DEFINE_STATIC_LOCAL(Vector<uint8_t>, linearRgbLUT, ());
+    if (linearRgbLUT.isEmpty()) {
+        linearRgbLUT.reserveCapacity(256);
+        for (unsigned i = 0; i < 256; i++) {
+            float color = i  / 255.0f;
+            color = (color <= 0.04045f ? color / 12.92f : pow((color + 0.055f) / 1.055f, 2.4f));
+            color = std::max(0.0f, color);
+            color = std::min(1.0f, color);
+            linearRgbLUT.append(static_cast<uint8_t>(round(color * 255)));
+        }
+    }
+    return linearRgbLUT;
+}
+
+const Vector<uint8_t>& getDeviceRgbLUT()
+{
+    DEFINE_STATIC_LOCAL(Vector<uint8_t>, deviceRgbLUT, ());

[Stephen Chennney, 2014/01/23 16:04:04]

Given that the return value gets converted immediately to a const unit_8 array,
why not just define it that way, and return a const unit_8* here too? I'm not
seeing any value in the Vector in this case.

+    if (deviceRgbLUT.isEmpty()) {
+        deviceRgbLUT.reserveCapacity(256);
+        for (unsigned i = 0; i < 256; i++) {
+            float color = i / 255.0f;
+            color = (powf(color, 1.0f / 2.4f) * 1.055f) - 0.055f;
+            color = std::max(0.0f, color);
+            color = std::min(1.0f, color);
+            deviceRgbLUT.append(static_cast<uint8_t>(round(color * 255)));
+        }
+    }
+    return deviceRgbLUT;
+}
+
+} // namespace
+
+const uint8_t* getConversionLUT(ColorSpace dstColorSpace, ColorSpace srcColorSpace)
+{
+    // Identity.
+    if (srcColorSpace == dstColorSpace)
+        return 0;
+
+    // Only sRGB/DeviceRGB <-> linearRGB are supported at the moment.
+    if ((srcColorSpace != ColorSpaceLinearRGB && srcColorSpace != ColorSpaceDeviceRGB)
+        || (dstColorSpace != ColorSpaceLinearRGB && dstColorSpace != ColorSpaceDeviceRGB))
+        return 0;
+
+    if (dstColorSpace == ColorSpaceLinearRGB)
+        return getLinearRgbLUT().data();
+    if (dstColorSpace == ColorSpaceDeviceRGB)
+        return getDeviceRgbLUT().data();
+
+    ASSERT_NOT_REACHED();
+    return 0;
+}
+
+Color convertColor(const Color& srcColor, ColorSpace dstColorSpace, ColorSpace srcColorSpace)
+{
+    const uint8_t* lookupTable = getConversionLUT(dstColorSpace, srcColorSpace);
+    if (!lookupTable)
+        return srcColor;
+
+    return Color(lookupTable[srcColor.red()], lookupTable[srcColor.green()], lookupTable[srcColor.blue()], srcColor.alpha());
+}
+
+} // namespace ColorSpaceUtilities
+
+} // namespace WebCore