Add an SkImageGeneratorCG

src/ports/SkImageGeneratorCG.cpp

Index: src/ports/SkImageGeneratorCG.cpp
diff --git a/src/ports/SkImageGeneratorCG.cpp b/src/ports/SkImageGeneratorCG.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..86c419d7205a31600677cac3ee18a7025ac2c8b3
--- /dev/null
+++ b/src/ports/SkImageGeneratorCG.cpp
@@ -0,0 +1,112 @@
+/*
+ * 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 "SkImageGeneratorCG.h"
+#include "SkUnpremultiply.h"
+
+#ifdef SK_BUILD_FOR_MAC
+#include <ApplicationServices/ApplicationServices.h>
+#endif
+
+#ifdef SK_BUILD_FOR_IOS
+#include <CoreGraphics/CoreGraphics.h>
+#include <ImageIO/ImageIO.h>
+#include <MobileCoreServices/MobileCoreServices.h>
+#endif
+
+static CGImageSourceRef data_to_CGImageSrc(SkData* data) {
+    CGDataProviderRef cgData = CGDataProviderCreateWithData(data, data->data(), data->size(),
+            nullptr);
+    if (!cgData) {
+        return nullptr;
+    }
+    CGImageSourceRef imageSrc = CGImageSourceCreateWithDataProvider(cgData, 0);
+    CGDataProviderRelease(cgData);
+    return imageSrc;
+}
+
+SkImageGenerator* SkImageGeneratorCG::NewFromEncodedCG(SkData* data) {
+    CGImageSourceRef imageSrc = data_to_CGImageSrc(data);
+    if (!imageSrc) {
+        return nullptr;
+    }
+    SkAutoTCallVProc<const void, CFRelease> autoImageSrc(imageSrc);

[scroggo, 2016/03/07 13:04:30]

Why do you treat this as a const void instead of a CGImageSourceRef?

[msarett, 2016/03/08 23:20:18]

CFRelease must be used to free the CGImageSrcRef, but CFRelease takes a const
void*.  So we must treat the imageSrc as a const void*.

I'll add a comment.

+
+    CFDictionaryRef properties = CGImageSourceCopyPropertiesAtIndex(imageSrc, 0, nullptr);
+    if (!properties) {
+        return nullptr;
+    }
+    
+    CFNumberRef widthRef = (CFNumberRef) (CFDictionaryGetValue(properties,
+            kCGImagePropertyPixelWidth));
+    CFNumberRef heightRef = (CFNumberRef) (CFDictionaryGetValue(properties,
+            kCGImagePropertyPixelHeight));
+    bool hasAlpha = (bool) (CFDictionaryGetValue(properties,
+            kCGImagePropertyHasAlpha));
+
+    int width, height;
+    CFNumberGetValue(widthRef, kCFNumberIntType, &width);

[scroggo, 2016/03/07 13:04:30]

It looks like these return whether or not they succeed (otherwise they would
just return the value you want, probably). We should probably check the return
value and exit early if they fail.

[msarett, 2016/03/08 23:20:17]

Done.

+    CFNumberGetValue(heightRef, kCFNumberIntType, &height);
+    
+    SkAlphaType alphaType = hasAlpha ? kPremul_SkAlphaType : kOpaque_SkAlphaType;
+    SkImageInfo info = SkImageInfo::Make(width, height, kN32_SkColorType, alphaType);
+
+    // FIXME: We have the opportunity to extract color space information here,
+    //        though I think it makes sense to wait until we understand how
+    //        we want to communicate it to the generator.
+
+    return new SkImageGeneratorCG(info, autoImageSrc.detach(), data);
+}
+
+SkImageGeneratorCG::SkImageGeneratorCG(const SkImageInfo& info, const void* imageSrc, SkData* data)
+    : INHERITED(info)
+    , fImageSrc(imageSrc)
+    , fData(SkRef(data))
+{}
+
+SkData* SkImageGeneratorCG::onRefEncodedData(SK_REFENCODEDDATA_CTXPARAM) {
+    return SkRef(fData.get());
+}
+
+bool SkImageGeneratorCG::onGetPixels(const SkImageInfo& info, void* pixels, size_t rowBytes,
+        SkPMColor ctable[], int* ctableCount) {
+    if (kN32_SkColorType != info.colorType()) {

[scroggo, 2016/03/07 13:04:30]

FIXME: Support other types?

[msarett, 2016/03/08 23:20:17]

Done.

+        return false;
+    }
+    
+    switch (info.alphaType()) {
+        case kOpaque_SkAlphaType:
+            if (kOpaque_SkAlphaType != this->getInfo().alphaType()) {
+                return false;
+            }
+            break;
+        case kPremul_SkAlphaType:
+            break;
+        default:
+            return false;
+    }
+    
+    CGImageRef image = CGImageSourceCreateImageAtIndex((CGImageSourceRef) fImageSrc.get(), 0,
+            nullptr);
+    if (!image) {
+        return false;
+    }
+    SkAutoTCallVProc<CGImage, CGImageRelease> autoImage(image);
+
+    // FIXME: Using this function (as opposed to swizzling ourselves) greatly
+    //        restricts the color and alpha types that we support.  If we

[scroggo, 2016/03/07 13:04:30]

I'd be curious about the performance difference, too, since we optimized the
swizzler with SIMD instructions.

[msarett, 2016/03/08 23:20:18]

Me too :).  Adding to the FIXME.

+    //        swizzle ourselves, we can add support for:
+    //            kUnpremul_SkAlphaType
+    //            16-bit per component RGBA
+    //            kGray_8_SkColorType
+    //            kIndex_8_SkColorType
+    if (!SkCopyPixelsFromCGImage(info, rowBytes, pixels, image)) {
+        return false;
+    }
+
+    return true;
+}