Improvements to readpixels GM

We don't support unpremultiplied images. Therefore:
- Don't test unpremul source images.
- After doing an unpremultiplying read, make sure to premul before drawing

For this to work with F16, add support for F16 sources to
SkColorSpaceXform.

Public API change is comments-only.
TBR=reed@google.com

BUG=skia:

Change-Id: Ie05b58231e99ca88cd7792b65ffbb4f390b01726
Reviewed-on: https://skia-review.googlesource.com/9900
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Matt Sarett <msarett@google.com>

gm/readpixels.cpp

@@ -10,6 +10,8 @@
 #include "SkCodec.h"
 #include "SkColorSpace.h"
 #include "SkColorSpace_Base.h"
+#include "SkColorSpaceXform.h"
+#include "SkColorSpaceXformPriv.h"
 #include "SkHalf.h"
 #include "SkImage.h"
 #include "SkPictureRecorder.h"
@@ -48,14 +50,14 @@ sk_sp<SkColorSpace> fix_for_colortype(SkColorSpace* colorSpace, SkColorType colo
 static const int kWidth = 64;
 static const int kHeight = 64;
 
-static sk_sp<SkImage> make_raster_image(SkColorType colorType, SkAlphaType alphaType) {
+static sk_sp<SkImage> make_raster_image(SkColorType colorType) {
     std::unique_ptr<SkStream> stream(GetResourceAsStream("google_chrome.ico"));
     std::unique_ptr<SkCodec> codec(SkCodec::NewFromStream(stream.release()));
 
     SkBitmap bitmap;
     SkImageInfo info = codec->getInfo().makeWH(kWidth, kHeight)
                                        .makeColorType(colorType)
-                                       .makeAlphaType(alphaType)
+                                       .makeAlphaType(kPremul_SkAlphaType)
             .makeColorSpace(fix_for_colortype(codec->getInfo().colorSpace(), colorType));
     bitmap.allocPixels(info);
     codec->getPixels(info, bitmap.getPixels(), bitmap.rowBytes());
@@ -132,6 +134,17 @@ static void draw_image(SkCanvas* canvas, SkImage* image, SkColorType dstColorTyp
                                             dstAlphaType, dstColorSpace);
     image->readPixels(dstInfo, data->writable_data(), rowBytes, 0, 0, hint);
 
+    // SkImage must be premul, so manually premul the data if we unpremul'd during readPixels
+    if (kUnpremul_SkAlphaType == dstAlphaType) {
+        auto xform = SkColorSpaceXform::New(dstColorSpace.get(), dstColorSpace.get());
+        if (!xform->apply(select_xform_format(dstColorType), data->writable_data(),
+                          select_xform_format(dstColorType), data->data(),
+                          image->width() * image->height(), kPremul_SkAlphaType)) {
+            memset(data->writable_data(), 0, rowBytes * image->height());
+        }
+        dstInfo = dstInfo.makeAlphaType(kPremul_SkAlphaType);
+    }
+
     // readPixels() does not always clamp F16.  The drawing code expects pixels in the 0-1 range.
     clamp_if_necessary(dstInfo, data->writable_data());
 
@@ -152,7 +165,7 @@ protected:
     }
 
     SkISize onISize() override {
-        return SkISize::Make(6 * kWidth, 18 * kHeight);
+        return SkISize::Make(6 * kWidth, 9 * kHeight);
     }
 
     void onDraw(SkCanvas* canvas) override {
@@ -178,19 +191,17 @@ protected:
 
         for (sk_sp<SkColorSpace> dstColorSpace : colorSpaces) {
             for (SkColorType srcColorType : colorTypes) {
-                for (SkAlphaType srcAlphaType : alphaTypes) {
-                    canvas->save();
-                    sk_sp<SkImage> image = make_raster_image(srcColorType, srcAlphaType);
-                    for (SkColorType dstColorType : colorTypes) {
-                        for (SkAlphaType dstAlphaType : alphaTypes) {
-                            draw_image(canvas, image.get(), dstColorType, dstAlphaType,
-                                       dstColorSpace, SkImage::kAllow_CachingHint);
-                            canvas->translate((float) kWidth, 0.0f);
-                        }
+                canvas->save();
+                sk_sp<SkImage> image = make_raster_image(srcColorType);
+                for (SkColorType dstColorType : colorTypes) {
+                    for (SkAlphaType dstAlphaType : alphaTypes) {
+                        draw_image(canvas, image.get(), dstColorType, dstAlphaType,
+                                   dstColorSpace, SkImage::kAllow_CachingHint);
+                        canvas->translate((float) kWidth, 0.0f);
                     }
-                    canvas->restore();
-                    canvas->translate(0.0f, (float) kHeight);
                 }
+                canvas->restore();
+                canvas->translate(0.0f, (float) kHeight);
             }
         }
     }

include/core/SkColorSpaceXform.h

@@ -32,15 +32,15 @@ public:
         kRGB_U16_BE_ColorFormat,   // Src only
         kRGBA_U16_BE_ColorFormat,  // Src only
 
-        kRGBA_F16_ColorFormat,     // Dst only
+        kRGBA_F16_ColorFormat,
         kRGBA_F32_ColorFormat,     // Dst only
     };
 
     /**
      *  Apply the color conversion to a |src| buffer, storing the output in the |dst| buffer.
      *
-     *  F16 and F32 are only supported as dst color formats, and only when the dst color space
-     *  is linear.  This function will return false in unsupported cases.
+     *  F32 is only supported as a dst color format. F16 and F32 are only supported when the color
+     *  space is linear. This function will return false in unsupported cases.
      *
      *  @param dst            Stored in the format described by |dstColorFormat|
      *  @param src            Stored in the format described by |srcColorFormat|

src/core/SkColorSpaceXform.cpp

@@ -1061,6 +1061,7 @@ bool SkColorSpaceXform_XYZ<kCSM>
     }
 
     if (kRGBA_F32_ColorFormat == dstColorFormat ||
+        kRGBA_F16_ColorFormat == srcColorFormat ||
         kRGBA_U16_BE_ColorFormat == srcColorFormat ||
         kRGB_U16_BE_ColorFormat == srcColorFormat ||
         kPremul_SkAlphaType == alphaType)
@@ -1163,6 +1164,12 @@ bool SkColorSpaceXform_XYZ<kCSM>
 
             pipeline.append(SkRasterPipeline::swap_rb);
             break;
+        case kRGBA_F16_ColorFormat:
+            if (kLinear_SrcGamma != fSrcGamma) {
+                return false;
+            }
+            pipeline.append(SkRasterPipeline::load_f16, &src);
+            break;
         case kRGBA_U16_BE_ColorFormat:
             switch (fSrcGamma) {
                 case kLinear_SrcGamma: