[ios][macos] Directly decode image files to non-premultiplied alpha images. Use [NSImage CGImageForProposedRect:context:hints:] instead of drawing into a bitmap representation

7 files changed, 49 insertions, 12 deletions

diff --git a/platform/darwin/mbgl/util/image+MGLAdditions.hpp b/platform/darwin/mbgl/util/image+MGLAdditions.hpp
index c738b4523d..df962cf76d 100644
--- a/platform/darwin/mbgl/util/image+MGLAdditions.hpp
+++ b/platform/darwin/mbgl/util/image+MGLAdditions.hpp
@@ -10,3 +10,7 @@ CGImageRef CGImageFromMGLPremultipliedImage(mbgl::PremultipliedImage&&);
 // Creates a PremultipliedImage by copying the pixels of the CGImage.
 // Does not alter the retain count of the supplied CGImage.
 mbgl::PremultipliedImage MGLPremultipliedImageFromCGImage(CGImageRef);
+
+// Creates an UnassociatedImage by copying the pixels of the CGImage.
+// Does not alter the retain count of the supplied CGImage.
+mbgl::UnassociatedImage MGLUnassociatedImageFromCGImage(CGImageRef src);
diff --git a/platform/darwin/src/MGLImageSource.mm b/platform/darwin/src/MGLImageSource.mm
index 0a2dc2713f..5e56e84220 100644
--- a/platform/darwin/src/MGLImageSource.mm
+++ b/platform/darwin/src/MGLImageSource.mm
@@ -60,8 +60,7 @@
 
 - (void)setImage:(MGLImage *)image {
     if (image != nullptr) {
-        mbgl::UnassociatedImage unassociatedImage = mbgl::util::unpremultiply(image.mgl_premultipliedImage);
-        self.rawSource->setImage(std::move(unassociatedImage));
+        self.rawSource->setImage(image.mgl_unassociatedImage);        
     } else {
         self.rawSource->setImage(mbgl::UnassociatedImage({0,0}));
     }
diff --git a/platform/darwin/src/image.mm b/platform/darwin/src/image.mm
index 57b680fbdb..72499b6fb6 100644
--- a/platform/darwin/src/image.mm
+++ b/platform/darwin/src/image.mm
@@ -81,6 +81,34 @@ mbgl::PremultipliedImage MGLPremultipliedImageFromCGImage(CGImageRef src) {
     return image;
 }
 
+mbgl::UnassociatedImage MGLUnassociatedImageFromCGImage(CGImageRef src) {
+    const size_t width = CGImageGetWidth(src);
+    const size_t height = CGImageGetHeight(src);
+
+    mbgl::UnassociatedImage image({ static_cast<uint32_t>(width), static_cast<uint32_t>(height) });
+
+    CGColorSpaceHandle colorSpace(CGColorSpaceCreateDeviceRGB());
+    if (!colorSpace) {
+        throw std::runtime_error("CGColorSpaceCreateDeviceRGB failed");
+    }
+
+    constexpr const size_t bitsPerComponent = 8;
+    constexpr const size_t bytesPerPixel = 4;
+    const size_t bytesPerRow = bytesPerPixel * width;
+
+    CGContextHandle context(CGBitmapContextCreate(
+        image.data.get(), width, height, bitsPerComponent, bytesPerRow, *colorSpace,
+        kCGBitmapByteOrderDefault | kCGImageAlphaNoneSkipLast));
+    if (!context) {
+        throw std::runtime_error("CGBitmapContextCreate failed");
+    }
+
+    CGContextSetBlendMode(*context, kCGBlendModeCopy);
+    CGContextDrawImage(*context, CGRectMake(0, 0, width, height), src);
+
+    return image;
+}
+
 namespace mbgl {
 
 PremultipliedImage decodeImage(const std::string& source) {
diff --git a/platform/ios/src/UIImage+MGLAdditions.h b/platform/ios/src/UIImage+MGLAdditions.h
index 6e15e07cb5..aeaf0f226f 100644
--- a/platform/ios/src/UIImage+MGLAdditions.h
+++ b/platform/ios/src/UIImage+MGLAdditions.h
@@ -12,6 +12,8 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (mbgl::PremultipliedImage)mgl_premultipliedImage;
 
+- (mbgl::UnassociatedImage)mgl_unassociatedImage;
+
 @end
 
 NS_ASSUME_NONNULL_END
diff --git a/platform/ios/src/UIImage+MGLAdditions.mm b/platform/ios/src/UIImage+MGLAdditions.mm
index 5e28d18190..80e6373eaa 100644
--- a/platform/ios/src/UIImage+MGLAdditions.mm
+++ b/platform/ios/src/UIImage+MGLAdditions.mm
@@ -32,4 +32,8 @@
 -(mbgl::PremultipliedImage)mgl_premultipliedImage {
     return MGLPremultipliedImageFromCGImage(self.CGImage);
 }
+
+- (mbgl::UnassociatedImage)mgl_unassociatedImage {
+    return MGLUnassociatedImageFromCGImage(self.CGImage);
+}
 @end
diff --git a/platform/macos/src/NSImage+MGLAdditions.h b/platform/macos/src/NSImage+MGLAdditions.h
index c08fc57bea..b997531c34 100644
--- a/platform/macos/src/NSImage+MGLAdditions.h
+++ b/platform/macos/src/NSImage+MGLAdditions.h
@@ -14,6 +14,8 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (mbgl::PremultipliedImage) mgl_premultipliedImage;
 
+- (mbgl::UnassociatedImage) mgl_unassociatedImage;
+
 @end
 
 NS_ASSUME_NONNULL_END
diff --git a/platform/macos/src/NSImage+MGLAdditions.mm b/platform/macos/src/NSImage+MGLAdditions.mm
index 6abe53e9ae..bfda98bc39 100644
--- a/platform/macos/src/NSImage+MGLAdditions.mm
+++ b/platform/macos/src/NSImage+MGLAdditions.mm
@@ -42,15 +42,13 @@
 }
 
 - (mbgl::PremultipliedImage)mgl_premultipliedImage {
-    // Create a bitmap image representation from the image, respecting backing
-    // scale factor and any resizing done on the image at runtime.
-    // http://www.cocoabuilder.com/archive/cocoa/82430-nsimage-getting-raw-bitmap-data.html#82431
-    [self lockFocus];
-    NSBitmapImageRep *rep = [[NSBitmapImageRep alloc] initWithFocusedViewRect:{ NSZeroPoint, self.size }];
-    [self unlockFocus];
-
-    mbgl::PremultipliedImage cPremultipliedImage({ static_cast<uint32_t>(rep.pixelsWide), static_cast<uint32_t>(rep.pixelsHigh) });
-    std::copy(rep.bitmapData, rep.bitmapData + cPremultipliedImage.bytes(), cPremultipliedImage.data.get());
-    return cPremultipliedImage;
+    CGImageRef ref = [self CGImageForProposedRect:nullptr context:nullptr hints:nullptr];
+    return MGLPremultipliedImageFromCGImage(ref);
 }
+
+- (mbgl::UnassociatedImage)mgl_unassociatedImage {
+    CGImageRef ref = [self CGImageForProposedRect:nullptr context:nullptr hints:nullptr];
+    return MGLUnassociatedImageFromCGImage(ref);
+}
+
 @end