POC implementation of a CoreText-based LocalGlyphRasterizer.

3 files changed, 131 insertions, 2 deletions

diff --git a/platform/darwin/src/local_glyph_rasterizer.mm b/platform/darwin/src/local_glyph_rasterizer.mm
new file mode 100644
index 0000000000..085774f75b
--- /dev/null
+++ b/platform/darwin/src/local_glyph_rasterizer.mm
@@ -0,0 +1,129 @@
+#include <mbgl/text/local_glyph_rasterizer.hpp>
+#include <mbgl/util/i18n.hpp>
+
+#import <Foundation/Foundation.h>
+
+namespace {
+
+template <typename T, typename S, void (*Releaser)(S)>
+struct CFHandle {
+    CFHandle(T t_): t(t_) {}
+    ~CFHandle() { Releaser(t); }
+    T operator*() { return t; }
+    operator bool() { return t; }
+private:
+    T t;
+};
+
+} // namespace
+
+
+namespace mbgl {
+
+/*
+    Initial implementation of darwin TinySDF support:
+    Draw any CJK glyphs using a default system font
+ 
+    Where to take this:
+     - Configure whether to use local fonts, and which fonts to use,
+       based on map or even style layer options
+     - Build heuristics for choosing fonts based on input FontStack
+       (maybe a globally configurable FontStack -> UIFontDescriptor map would make sense?
+     - Extract glyph metrics so that this can be used with more than just fixed width glyphs
+*/
+
+bool LocalGlyphRasterizer::canRasterizeGlyph(const FontStack&, GlyphID glyphID) {
+    // TODO: This is a rough approximation of the set of glyphs that will work with fixed glyph metrics
+    // Either narrow this down to be conservative, or actually extract glyph metrics in rasterizeGlyph
+    return util::i18n::allowsIdeographicBreaking(glyphID);
+}
+
+using CGContextHandle = CFHandle<CGContextRef, CGContextRef, CGContextRelease>;
+using CGColorSpaceHandle = CFHandle<CGColorSpaceRef, CGColorSpaceRef, CGColorSpaceRelease>;
+
+Glyph LocalGlyphRasterizer::rasterizeGlyph(const FontStack&, GlyphID glyphID) {
+    Glyph fixedMetrics;
+    fixedMetrics.id = glyphID;
+
+    fixedMetrics.metrics.width = 24;
+    fixedMetrics.metrics.height = 24;
+    fixedMetrics.metrics.left = 0;
+    fixedMetrics.metrics.top = -8;
+    fixedMetrics.metrics.advance = 24;
+
+    uint32_t width = 30;
+    uint32_t height = 30;
+    Size size(width, height);
+
+    fixedMetrics.bitmap = AlphaImage(size);
+    
+    NSDictionary *fontAttributes =
+              [NSDictionary dictionaryWithObjectsAndKeys:
+                      [NSNumber numberWithFloat:24.0], (NSString *)kCTFontSizeAttribute,
+                      nil];
+    // Create a descriptor.
+    CTFontDescriptorRef descriptor =
+              CTFontDescriptorCreateWithAttributes((CFDictionaryRef)fontAttributes);
+
+    // Create a font using the descriptor.
+    CTFontRef font = CTFontCreateWithFontDescriptor(descriptor, 0.0, NULL);
+    CFRelease(descriptor);
+
+
+    CFStringRef string = CFStringCreateWithCharacters(NULL, (UniChar*)&glyphID, 1);
+
+    PremultipliedImage image(size);
+
+    CGColorSpaceHandle colorSpace(CGColorSpaceCreateDeviceRGB());
+    // TODO: Is there a way to just draw a single alpha channel instead of copying it out of an RGB image? Doesn't seem like the grayscale colorspace is what I'm looking for...
+    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 | kCGImageAlphaPremultipliedLast));
+    if (!context) {
+        throw std::runtime_error("CGBitmapContextCreate failed");
+    }
+
+    CFStringRef keys[] = { kCTFontAttributeName };
+    CFTypeRef values[] = { font };
+
+    CFDictionaryRef attributes =
+        CFDictionaryCreate(kCFAllocatorDefault, (const void**)&keys,
+            (const void**)&values, sizeof(keys) / sizeof(keys[0]),
+            &kCFTypeDictionaryKeyCallBacks,
+            &kCFTypeDictionaryValueCallBacks);
+
+    CFAttributedStringRef attrString =
+        CFAttributedStringCreate(kCFAllocatorDefault, string, attributes);
+    CFRelease(string);
+    CFRelease(attributes);
+
+    CTLineRef line = CTLineCreateWithAttributedString(attrString); // TODO: Get glyph runs (for metric extraction) and use showGlyphs API instead?
+
+    // Set text position and draw the line into the graphics context
+    CGContextSetTextPosition(*context, 0.0, 0.0);
+    CTLineDraw(line, *context);
+    CFRelease(line);
+    CFRelease(font);
+    CFRelease(string); // TODO: Surely leaking something here, wrap these up!
+    
+    for (uint32_t i = 0; i < width * height; i++) {
+        fixedMetrics.bitmap.data[i] = image.data[4 * i + 3]; // alpha value
+    }
+
+    return fixedMetrics;
+}
+
+} // namespace mbgl
diff --git a/platform/ios/config.cmake b/platform/ios/config.cmake
index 3b99211299..2cc16bbbc2 100644
--- a/platform/ios/config.cmake
+++ b/platform/ios/config.cmake
@@ -28,11 +28,11 @@ macro(mbgl_platform_core)
         # Misc
         PRIVATE platform/darwin/mbgl/storage/reachability.h
         PRIVATE platform/darwin/mbgl/storage/reachability.m
+        PRIVATE platform/darwin/src/local_glyph_rasterizer.mm
         PRIVATE platform/darwin/src/logging_nslog.mm
         PRIVATE platform/darwin/src/nsthread.mm
         PRIVATE platform/darwin/src/string_nsstring.mm
         PRIVATE platform/default/bidi.cpp
-        PRIVATE platform/default/local_glyph_rasterizer.cpp
         PRIVATE platform/default/thread_local.cpp
         PRIVATE platform/default/utf.cpp
 
diff --git a/platform/macos/config.cmake b/platform/macos/config.cmake
index 677c2c5fd5..21663885d4 100644
--- a/platform/macos/config.cmake
+++ b/platform/macos/config.cmake
@@ -14,11 +14,11 @@ macro(mbgl_platform_core)
         # Misc
         PRIVATE platform/darwin/mbgl/storage/reachability.h
         PRIVATE platform/darwin/mbgl/storage/reachability.m
+        PRIVATE platform/darwin/src/local_glyph_rasterizer.mm
         PRIVATE platform/darwin/src/logging_nslog.mm
         PRIVATE platform/darwin/src/nsthread.mm
         PRIVATE platform/darwin/src/string_nsstring.mm
         PRIVATE platform/default/bidi.cpp
-        PRIVATE platform/default/local_glyph_rasterizer.cpp
         PRIVATE platform/default/thread_local.cpp
         PRIVATE platform/default/utf.cpp