Add SkEncodedInfo to report properties of encoded image data

include/codec/SkEncodedInfo.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkEncodedInfo_DEFINED
+#define SkEncodedInfo_DEFINED
+
+#include "SkImageInfo.h"
+
+struct SkEncodedInfo {
+public:
+
+    enum Alpha {
+        kOpaque_Alpha,
+        kUnpremul_Alpha,
+
+        // Each pixel is either fully opaque or fully transparent.

[reed1, 2016/04/07 15:08:01]

Are there no native premul image formats (e.g. webp?)

[msarett, 2016/04/07 15:24:49]

As far as I know, nothing is kPremul.  We allow libwebp to premultiply for us,
but the image is encoded as kUnpremul.

+        // There is no difference between requesting kPremul or kUnpremul.
+        kBinary_Alpha,
+
+        // Allows us to have a default constructor.  Should be treated as
+        // invalid.
+        kUnknown_Alpha,
+    };
+
+    /*
+     * We strive to make the number of components per pixel obvious through
+     * our naming conventions.
+     * Ex: kRGB has 3 components.  kRGBA has 4 components.
+     *
+     * This sometimes results in redundant Alpha and Color information.
+     * Ex: kRGB images must also be kOpaque.
+     */
+    enum Color {
+        // PNG, WBMP
+        kGray_Color,
+
+        // PNG
+        kGrayAlpha_Color,
+
+        // PNG, GIF, BMP
+        kPalette_Color,
+
+        // PNG, RAW
+        kRGB_Color,
+        kRGBA_Color,
+
+        // BMP
+        kBGR_Color,
+        kBGRX_Color,
+        kBGRA_Color,
+
+        // JPEG, WEBP
+        kYUV_Color,
+
+        // WEBP
+        kYUVA_Color,
+
+        // JPEG
+        // Photoshop actually writes inverted CMYK data into JPEGs, where zero
+        // represents 100% ink coverage.  For this reason, we treat CMYK JPEGs
+        // as having inverted CMYK.  libjpeg-turbo warns that this may break
+        // other applications, but the CMYK JPEGs we see on the web expect to
+        // be treated as inverted CMYK.
+        kInvertedCMYK_Color,
+        kYCCK_Color,
+
+        // Allows us to have a default constructor.  Should be treated as
+        // invalid.
+        kUnknown_Color,
+    };
+
+    static SkEncodedInfo Make(const SkISize& size, Color color, Alpha alpha, int bitsPerComponent) {
+        return SkEncodedInfo::Make(size.width(), size.height(), color, alpha, bitsPerComponent);
+    }
+
+    static SkEncodedInfo Make(int width, int height, Color color, Alpha alpha,
+            int bitsPerComponent) {
+        SkASSERT(width > 0 && height > 0);
+
+        SkASSERT(1 == bitsPerComponent ||
+                 2 == bitsPerComponent ||
+                 4 == bitsPerComponent ||
+                 8 == bitsPerComponent ||
+                 16 == bitsPerComponent);
+
+        switch (color) {
+            case kGray_Color:
+                SkASSERT(kOpaque_Alpha == alpha);
+                break;
+            case kGrayAlpha_Color:
+                SkASSERT(kOpaque_Alpha != alpha);
+                break;
+            case kPalette_Color:
+                SkASSERT(16 != bitsPerComponent);
+                break;
+            case kRGB_Color:
+            case kBGR_Color:
+            case kBGRX_Color:
+                SkASSERT(kOpaque_Alpha == alpha);
+                SkASSERT(bitsPerComponent >= 8);
+                break;
+            case kYUV_Color:
+            case kInvertedCMYK_Color:
+            case kYCCK_Color:
+                SkASSERT(kOpaque_Alpha == alpha);
+                SkASSERT(8 == bitsPerComponent);
+                break;
+            case kRGBA_Color:
+                SkASSERT(kOpaque_Alpha != alpha);
+                SkASSERT(bitsPerComponent >= 8);
+                break;
+            case kBGRA_Color:
+            case kYUVA_Color:
+                SkASSERT(kOpaque_Alpha != alpha);
+                SkASSERT(8 == bitsPerComponent);
+                break;
+            default:
+                SkASSERT(false);
+                break;
+        }
+
+        return SkEncodedInfo(width, height, color, alpha, bitsPerComponent);
+    }
+
+    /*
+     * Returns an SkImageInfo with Skia color and alpha types that are the
+     * closest possible match to the encoded info.
+     */
+    SkImageInfo makeImageInfo() const {
+        switch (fColor) {
+            case kGray_Color:
+                SkASSERT(kOpaque_Alpha == fAlpha);
+                return SkImageInfo::Make(fWidth, fHeight, kGray_8_SkColorType, kOpaque_SkAlphaType);
+            case kGrayAlpha_Color:
+                SkASSERT(kOpaque_Alpha != fAlpha);
+                return SkImageInfo::Make(fWidth, fHeight, kGray_8_SkColorType,
+                        kUnpremul_SkAlphaType);
+            case kPalette_Color: {
+                SkAlphaType alphaType = (kOpaque_Alpha == fAlpha) ? kOpaque_SkAlphaType :
+                        kUnpremul_SkAlphaType;
+                return SkImageInfo::Make(fWidth, fHeight, kIndex_8_SkColorType, alphaType);
+            }
+            case kRGB_Color:
+            case kBGR_Color:
+            case kBGRX_Color:
+            case kYUV_Color:
+            case kInvertedCMYK_Color:
+            case kYCCK_Color:
+                SkASSERT(kOpaque_Alpha == fAlpha);
+                return SkImageInfo::Make(fWidth, fHeight, kN32_SkColorType, kOpaque_SkAlphaType);
+            case kRGBA_Color:
+            case kBGRA_Color:
+            case kYUVA_Color:
+                SkASSERT(kOpaque_Alpha != fAlpha);
+                return SkImageInfo::Make(fWidth, fHeight, kN32_SkColorType, kUnpremul_SkAlphaType);
+            default:
+                SkASSERT(false);
+                return SkImageInfo::MakeUnknown();
+        }
+    }
+
+    int width() const { return fWidth; }
+    int height() const { return fHeight; }
+
+    SkEncodedInfo()
+        : fWidth(0)
+        , fHeight(0)
+        , fColor(kUnknown_Color)
+        , fAlpha(kUnknown_Alpha)
+        , fBitsPerComponent(0)
+    {}
+
+private:
+
+    SkEncodedInfo(int width, int height, Color color, Alpha alpha, uint8_t bitsPerComponent)
+        : fWidth(width)
+        , fHeight(height)
+        , fColor(color)
+        , fAlpha(alpha)
+        , fBitsPerComponent(bitsPerComponent)
+    {}
+
+    int     fWidth;
+    int     fHeight;
+    Color   fColor;
+    Alpha   fAlpha;
+    uint8_t fBitsPerComponent;
+};
+
+#endif