[PDF] Add unpremultiply support and a GM.

This is a resubmit of https://codereview.chromium.org/22831039 which was
reverted because it causes issues on Windows.

BUG=chromium:175548
R=edisonn@google.com

Review URL: https://codereview.chromium.org/27518003

git-svn-id: http://skia.googlecode.com/svn/trunk/src@11857 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/pdf/SkPDFImage.cpp b/pdf/SkPDFImage.cpp
index 19ad79e..78f1f6d 100644
--- a/pdf/SkPDFImage.cpp
+++ b/pdf/SkPDFImage.cpp
@@ -336,6 +336,157 @@
     return result;
 }
 
+/**
+ * Removes the alpha component of an ARGB color (including unpremultiply) while
+ * keeping the output in the same format as the input.
+ */
+static uint32_t remove_alpha_argb8888(uint32_t pmColor) {
+    SkColor color = SkUnPreMultiply::PMColorToColor(pmColor);
+    return SkPackARGB32NoCheck(SK_AlphaOPAQUE,
+                               SkColorGetR(color),
+                               SkColorGetG(color),
+                               SkColorGetB(color));
+}
+
+static uint16_t remove_alpha_argb4444(uint16_t pmColor) {
+    return SkPixel32ToPixel4444(
+            remove_alpha_argb8888(SkPixel4444ToPixel32(pmColor)));
+}
+
+static uint32_t get_argb8888_neighbor_avg_color(const SkBitmap& bitmap,
+                                                int xOrig, int yOrig) {
+    uint8_t count = 0;
+    uint16_t r = 0;
+    uint16_t g = 0;
+    uint16_t b = 0;
+
+    for (int y = yOrig - 1; y <= yOrig + 1; y++) {
+        if (y < 0 || y >= bitmap.height()) {
+            continue;
+        }
+        uint32_t* src = bitmap.getAddr32(0, y);
+        for (int x = xOrig - 1; x <= xOrig + 1; x++) {
+            if (x < 0 || x >= bitmap.width()) {
+                continue;
+            }
+            if (SkGetPackedA32(src[x]) != SK_AlphaTRANSPARENT) {
+                uint32_t color = remove_alpha_argb8888(src[x]);
+                r += SkGetPackedR32(color);
+                g += SkGetPackedG32(color);
+                b += SkGetPackedB32(color);
+                count++;
+            }
+        }
+    }
+
+    if (count == 0) {
+        return SkPackARGB32NoCheck(SK_AlphaOPAQUE, 0, 0, 0);
+    } else {
+        return SkPackARGB32NoCheck(SK_AlphaOPAQUE,
+                                   r / count, g / count, b / count);
+    }
+}
+
+static uint16_t get_argb4444_neighbor_avg_color(const SkBitmap& bitmap,
+                                                int xOrig, int yOrig) {
+    uint8_t count = 0;
+    uint8_t r = 0;
+    uint8_t g = 0;
+    uint8_t b = 0;
+
+    for (int y = yOrig - 1; y <= yOrig + 1; y++) {
+        if (y < 0 || y >= bitmap.height()) {
+            continue;
+        }
+        uint16_t* src = bitmap.getAddr16(0, y);
+        for (int x = xOrig - 1; x <= xOrig + 1; x++) {
+            if (x < 0 || x >= bitmap.width()) {
+                continue;
+            }
+            if ((SkGetPackedA4444(src[x]) & 0x0F) != SK_AlphaTRANSPARENT) {
+                uint16_t color = remove_alpha_argb4444(src[x]);
+                r += SkGetPackedR4444(color);
+                g += SkGetPackedG4444(color);
+                b += SkGetPackedB4444(color);
+                count++;
+            }
+        }
+    }
+
+    if (count == 0) {
+        return SkPackARGB4444(SK_AlphaOPAQUE & 0x0F, 0, 0, 0);
+    } else {
+        return SkPackARGB4444(SK_AlphaOPAQUE & 0x0F,
+                                   r / count, g / count, b / count);
+    }
+}
+
+static SkBitmap unpremultiply_bitmap(const SkBitmap& bitmap,
+                                     const SkIRect& srcRect) {
+    SkBitmap outBitmap;
+    outBitmap.setConfig(bitmap.config(), srcRect.width(), srcRect.height());
+    SkASSERT(outBitmap.allocPixels());
+    size_t dstRow = 0;
+
+    outBitmap.lockPixels();
+    bitmap.lockPixels();
+    switch (bitmap.config()) {
+        case SkBitmap::kARGB_4444_Config: {
+            for (int y = srcRect.fTop; y < srcRect.fBottom; y++) {
+                uint16_t* dst = outBitmap.getAddr16(0, dstRow);
+                uint16_t* src = bitmap.getAddr16(0, y);
+                for (int x = srcRect.fLeft; x < srcRect.fRight; x++) {
+                    uint8_t a = SkGetPackedA4444(src[x]);
+                    // It is necessary to average the color component of
+                    // transparent pixels with their surrounding neighbors
+                    // since the PDF renderer may separately re-sample the
+                    // alpha and color channels when the image is not
+                    // displayed at its native resolution. Since an alpha of
+                    // zero gives no information about the color component,
+                    // the pathological case is a white image with sharp
+                    // transparency bounds - the color channel goes to black,
+                    // and the should-be-transparent pixels are rendered
+                    // as grey because of the separate soft mask and color
+                    // resizing.
+                    if (a == (SK_AlphaTRANSPARENT & 0x0F)) {
+                        *dst = get_argb4444_neighbor_avg_color(bitmap, x, y);
+                    } else {
+                        *dst = remove_alpha_argb4444(src[x]);
+                    }
+                    dst++;
+                }
+                dstRow++;
+            }
+            break;
+        }
+        case SkBitmap::kARGB_8888_Config: {
+            for (int y = srcRect.fTop; y < srcRect.fBottom; y++) {
+                uint32_t* dst = outBitmap.getAddr32(0, dstRow);
+                uint32_t* src = bitmap.getAddr32(0, y);
+                for (int x = srcRect.fLeft; x < srcRect.fRight; x++) {
+                    uint8_t a = SkGetPackedA32(src[x]);
+                    if (a == SK_AlphaTRANSPARENT) {
+                        *dst = get_argb8888_neighbor_avg_color(bitmap, x, y);
+                    } else {
+                        *dst = remove_alpha_argb8888(src[x]);
+                    }
+                    dst++;
+                }
+                dstRow++;
+            }
+            break;
+        }
+        default:
+            SkASSERT(false);
+    }
+    bitmap.unlockPixels();
+    outBitmap.unlockPixels();
+
+    outBitmap.setImmutable();
+
+    return outBitmap;
+}
+
 // static
 SkPDFImage* SkPDFImage::CreateImage(const SkBitmap& bitmap,
                                     const SkIRect& srcRect,
@@ -358,8 +509,16 @@
         return NULL;
     }
 
-    SkPDFImage* image = SkNEW_ARGS(SkPDFImage, (NULL, bitmap,
-                                                false, srcRect, encoder));
+    SkPDFImage* image;
+    SkBitmap::Config config = bitmap.config();
+    if (alphaData.get() != NULL && (config == SkBitmap::kARGB_8888_Config ||
+            config == SkBitmap::kARGB_4444_Config)) {
+        SkBitmap unpremulBitmap = unpremultiply_bitmap(bitmap, srcRect);
+        image = SkNEW_ARGS(SkPDFImage, (NULL, unpremulBitmap, false, NULL,
+                                        encoder));
+    } else {
+        image = SkNEW_ARGS(SkPDFImage, (NULL, bitmap, false, srcRect, encoder));
+    }
     if (alphaData.get() != NULL) {
         SkAutoTUnref<SkPDFImage> mask(
                 SkNEW_ARGS(SkPDFImage, (alphaData.get(), bitmap,