Add index-8 sampler to the pipeline.

src/core/SkLinearBitmapPipeline.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkLinearBitmapPipeline.h"
 
 #include "SkPM4f.h"
@@ skipping 440 matching lines @@
                 sampleStage->Initialize<Sampler<Pixel8888LRGB, Placer>>(next, srcPixmap);
             }
             break;
         case kBGRA_8888_SkColorType:
             if (imageInfo.profileType() == kSRGB_SkColorProfileType) {
                 sampleStage->Initialize<Sampler<Pixel8888SBGR, Placer>>(next, srcPixmap);
             } else {
                 sampleStage->Initialize<Sampler<Pixel8888LBGR, Placer>>(next, srcPixmap);
             }
             break;
+        case kIndex_8_SkColorType:
+            if (imageInfo.profileType() == kSRGB_SkColorProfileType) {
+                sampleStage->Initialize<Sampler<PixelIndex8SRGB, Placer>>(next, srcPixmap);
+            } else {
+                sampleStage->Initialize<Sampler<PixelIndex8LRGB, Placer>>(next, srcPixmap);
+            }
+            break;
         default:
             SkFAIL("Not implemented. Unsupported src");
             break;
     }
     return sampleStage->get();
 }
 
 SkLinearBitmapPipeline::BilerpProcessorInterface* choose_pixel_sampler(
     Placer* next,
     SkFilterQuality filterQuality,
@@ skipping 79 matching lines @@
         if (inverse.getScaleX() >= 0.0f) {
             adjustedInverse.setTranslateX(
                 nextafterf(inverse.getTranslateX(), std::floor(inverse.getTranslateX())));
         }
         if (inverse.getScaleY() >= 0.0f) {
             adjustedInverse.setTranslateY(
                 nextafterf(inverse.getTranslateY(), std::floor(inverse.getTranslateY())));
         }
     }
 
+    // If it is an index 8 color type, the sampler converts to unpremul for better fidelity.
+    SkAlphaType alphaType = srcImageInfo.alphaType();
+    if (srcPixmap.colorType() == kIndex_8_SkColorType) {
+        alphaType = kUnpremul_SkAlphaType;
+    }
+
     // As the stages are built, the chooser function may skip a stage. For example, with the
     // identity matrix, the matrix stage is skipped, and the tilerStage is the first stage.
-    auto placementStage = choose_pixel_placer(srcImageInfo.alphaType(), postAlpha, &fPixelStage);
+    auto placementStage = choose_pixel_placer(alphaType, postAlpha, &fPixelStage);
     auto samplerStage   = choose_pixel_sampler(placementStage,
                                                filterQuality, srcPixmap, &fSampleStage);
     auto tilerStage     = choose_tiler(samplerStage,
                                        dimensions, xTile, yTile, filterQuality, &fTiler);
     fFirstStage         = choose_matrix(tilerStage, adjustedInverse, &fMatrixStage);
 }
 
 void SkLinearBitmapPipeline::shadeSpan4f(int x, int y, SkPM4f* dst, int count) {
     SkASSERT(count > 0);
     fPixelStage->setDestination(dst);
     // The count and length arguments start out in a precise relation in order to keep the
     // math correct through the different stages. Count is the number of pixel to produce.
     // Since the code samples at pixel centers, length is the distance from the center of the
     // first pixel to the center of the last pixel. This implies that length is count-1.
     fFirstStage->pointSpan(Span{{x + 0.5f, y + 0.5f}, count - 1.0f, count});
 }