separate IBL from skybox and add setBackgroundImage method

ios/include/imageio/ImageDecoder.h

@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef IMAGE_IMAGEDECODER_H_
+#define IMAGE_IMAGEDECODER_H_
+
+#include <iosfwd>
+#include <string>
+
+#include <image/LinearImage.h>
+
+#include <utils/compiler.h>
+
+namespace image {
+
+class UTILS_PUBLIC ImageDecoder {
+public:
+    enum class ColorSpace {
+        LINEAR,
+        SRGB
+    };
+
+    // Returns linear floating-point data, or a non-valid image if an error occured.
+    static LinearImage decode(std::istream& stream, const std::string& sourceName,
+            ColorSpace sourceSpace = ColorSpace::SRGB);
+
+    class Decoder {
+    public:
+        virtual LinearImage decode() = 0;
+        virtual ~Decoder() = default;
+
+        ColorSpace getColorSpace() const noexcept {
+            return mColorSpace;
+        }
+
+        void setColorSpace(ColorSpace colorSpace) noexcept {
+            mColorSpace = colorSpace;
+        }
+
+    private:
+        ColorSpace mColorSpace = ColorSpace::SRGB;
+    };
+
+private:
+    enum class Format {
+        NONE,
+        PNG,
+        HDR,
+        PSD,
+        EXR
+    };
+};
+
+} // namespace image
+
+#endif /* IMAGE_IMAGEDECODER_H_ */