opal/bridge: implement bridge between GUI and Opal types

Implement a bridge between NSColor and CGColorRef and a stub for a
bridge between NSImage and CGImageRef. This improves compatibility with
Quartz.

Source/opal/GNUmakefile

@@ -37,6 +37,7 @@ opal_OBJC_FILES = OpalSurface.m \
   OpalFaceInfo.m \
   OpalPSSurface.m \
   OpalPDFSurface.m \
+  OpalBridge.m \
   ../fontconfig/FCFaceInfo.m \
   ../fontconfig/FCFontEnumerator.m \
   ../fontconfig/FCFontInfo.m \

Source/opal/OpalBridge.m

@@ -0,0 +1,116 @@
+/*
+   OpalBridge.m
+
+   Copyright (C) 2017 Free Software Foundation, Inc.
+
+   Author: Daniel Ferreira <dtf@stanford.edu>
+   Date: July 2017
+
+   This file is part of GNUstep.
+
+   This library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2 of the License, or (at your option) any later version.
+
+   This library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with this library; see the file COPYING.LIB.
+   If not, see <http://www.gnu.org/licenses/> or write to the
+   Free Software Foundation, 51 Franklin Street, Fifth Floor,
+   Boston, MA 02110-1301, USA.
+*/
+
+#import <AppKit/NSColor.h>
+#import <AppKit/NSImage.h>
+#import <AppKit/NSColorSpace.h>
+#import <AppKit/NSGraphics.h>
+#import <CoreGraphics/CGColor.h>
+#import <CoreGraphics/CGImage.h>
+#import <objc/runtime.h>
+
+@implementation NSColor (GSQuartz)
+/*
+ * FIXME:
+ * NOTE 1: GNUstep-GUI does not allow an NSColor to be created with a custom
+ * NSColorSpace. If this were allowed, we'd have to:
+ *   1) implement a bridge for -[NSColorSpace CGColorSpace]
+ *   2) for each color, extract that color space and generate a CGColorRef.
+ * NOTE 2: GNUstep-GUI makes no distinction of device and generic color spaces.
+ * If this ever ceases to be the case, some adjustment might be necessary here.
+ */
+- (CGColorRef)CGColor
+{
+  NSString *name = [self colorSpaceName];
+  
+  // FIXME: we should handle black color spaces here, which we currently
+  // ignore in the implementation.
+  CFStringRef cgColorSpaceName = NULL;
+  if ([name isEqualToString: NSCalibratedRGBColorSpace]
+    || [name isEqualToString: NSDeviceRGBColorSpace])
+    cgColorSpaceName = kCGColorSpaceSRGB;
+  else if ([name isEqualToString: NSCalibratedBlackColorSpace]
+    || [name isEqualToString: NSCalibratedWhiteColorSpace]
+    || [name isEqualToString: NSDeviceBlackColorSpace]
+    || [name isEqualToString: NSDeviceWhiteColorSpace])
+    cgColorSpaceName = kCGColorSpaceGenericGray;
+  else if ([name isEqualToString: NSDeviceCMYKColorSpace])
+    cgColorSpaceName = kCGColorSpaceGenericCMYK;
+  else if ([name isEqualToString: NSNamedColorSpace])
+    return [[self colorUsingColorSpaceName: NSDeviceRGBColorSpace] CGColor];
+
+  if (cgColorSpaceName == NULL)
+    return NULL;
+
+  CGColorSpaceRef colorSpace = CGColorSpaceCreateWithName(cgColorSpaceName);
+  CGFloat values[10];
+  [self getComponents: values];
+
+  CGColorRef color = CGColorCreate(colorSpace, values);
+  CFRelease(colorSpace);
+
+  return (CGColorRef)[(id)color autorelease];
+}
+@end
+
+@implementation NSImageRep (GSQuartz)
+- (CGImageRef)CGImageForProposedRect: (NSRect *)proposedDestRect 
+                             context: (NSGraphicsContext *)referenceContext 
+                               hints: (NSDictionary *)hints
+{
+  /*
+   * FIXME Must implement this.
+   * A note for future implementors:
+    > Apparently each NSImageRep subclass implements this method, with the
+    > base implementation being[1], as I understand it (which may be wrong):
+    > i. create a new blank context with *proposedDestRect.size and set it
+    > as the current context. This context should theoretically be
+    > constructed with properties extracted from `referenceContext` and/or
+    > `hints`, although I suppose our first implementation can go without
+    > that.
+    > ii. call [self draw];
+    > iii. adjust *proposedDestRect to round half-pixels
+    > iv. extract a CGImage from the bitmap context
+    > If NSImage.size == *proposedDestRect.size, we should just CGImageCreate
+    > directly from our representation data.
+   */
+
+  return NULL;
+}
+@end
+
+@implementation NSImage (GSQuartz)
+- (CGImageRef)CGImageForProposedRect: (NSRect *)proposedDestRect 
+                             context: (NSGraphicsContext *)referenceContext 
+                               hints: (NSDictionary *)hints
+{
+  // FIXME: Must implement this.
+  // This should pick the best NSImageRep for this NSImage and call
+  // -[NSImageRep CGImageForProposedRect:...].
+  return NULL;
+}
+@end