[ios, macos] possibility to set custom images to style (#6637)

* [ios, macos] possibility to set custom images to style

* [ios, macos] setImage:forName now supports MGLImage (UIImage/NSImage)

* [ios, macos] update documentation for setImage:forName: and removeImageForName:

* [ios, macos] rename method and fix prefix

* [ios, macos] change header visibility to project

* [ios, macos] update header imports

* [ios, macos] delete unnecessary whitespaces

* [ios, macos] remove unnecessary nil checks

* [ios, macos] delete unnecessary whitespaces

* [ios, macos] update documentation

* [ios, macos] make mgl_spriteImage a parameter-less instance method

* [ios, macos] add asserts

1 files changed, 27 insertions, 0 deletions

diff --git a/platform/ios/src/UIImage+MGLAdditions.mm b/platform/ios/src/UIImage+MGLAdditions.mm
new file mode 100644
index 0000000000..8ec8f9e15f
--- /dev/null
+++ b/platform/ios/src/UIImage+MGLAdditions.mm
@@ -0,0 +1,27 @@
+#import "UIImage+MGLAdditions.h"
+
+@implementation UIImage (MGLAdditions)
+
+- (std::unique_ptr<mbgl::SpriteImage>)mgl_spriteImage
+{
+    CGImageRef cgImage = self.CGImage;
+    size_t width = CGImageGetWidth(cgImage);
+    size_t height = CGImageGetHeight(cgImage);
+    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
+    mbgl::PremultipliedImage cPremultipliedImage(width, height);
+    size_t bytesPerPixel = 4;
+    size_t bytesPerRow = bytesPerPixel * width;
+    size_t bitsPerComponent = 8;
+
+    CGContextRef context = CGBitmapContextCreate(cPremultipliedImage.data.get(),
+      width, height, bitsPerComponent, bytesPerRow,
+      colorSpace, kCGImageAlphaPremultipliedLast);
+
+    CGContextDrawImage(context, CGRectMake(0, 0, width, height), cgImage);
+    CGContextRelease(context);
+    CGColorSpaceRelease(colorSpace);
+
+    return std::make_unique<mbgl::SpriteImage>(std::move(cPremultipliedImage), float(self.scale));
+}
+
+@end