[ios] POC: implementation of a CoreText-based LocalGlyphRasterizer

include/mbgl/renderer/renderer.hpp

@@ -25,7 +25,8 @@ class Renderer {
 public:
     Renderer(RendererBackend&, float pixelRatio_, FileSource&, Scheduler&,
              GLContextMode = GLContextMode::Unique,
-             const optional<std::string> programCacheDir = {});
+             const optional<std::string> programCacheDir = {},
+             const optional<std::string> localFontFamily = {});
     ~Renderer();
 
     void markContextLost();

platform/darwin/src/CFHandle.hpp

@@ -0,0 +1,31 @@
+#pragma once
+
+/*
+  CFHandle is a minimal wrapper designed to hold and release CoreFoundation-style handles
+  It is non-transferrable: wrap it in something like a unique_ptr if you need to pass it around,
+  or just use unique_ptr with a custom deleter.
+  CFHandle has no special treatment for null handles -- be careful not to let it hold a null
+  handle if the behavior of the Releaser isn't defined for null.
+
+  ex:
+   using CFDataHandle = CFHandle<CFDataRef, CFTypeRef, CFRelease>;
+
+   CFDataHandle data(CFDataCreateWithBytesNoCopy(
+        kCFAllocatorDefault, reinterpret_cast<const unsigned char*>(source.data()), source.size(),
+        kCFAllocatorNull));
+*/
+
+namespace {
+
+template <typename HandleType, typename ReleaserArgumentType, void (*Releaser)(ReleaserArgumentType)>
+struct CFHandle {
+    CFHandle(HandleType handle_): handle(handle_) {}
+    ~CFHandle() { Releaser(handle); }
+    HandleType operator*() { return handle; }
+    operator bool() { return handle; }
+private:
+    HandleType handle;
+};
+
+} // namespace
+

platform/darwin/src/image.mm

@@ -2,19 +2,7 @@
 
 #import <ImageIO/ImageIO.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
+#import "CFHandle.hpp"
 
 using CGImageHandle = CFHandle<CGImageRef, CGImageRef, CGImageRelease>;
 using CFDataHandle = CFHandle<CFDataRef, CFTypeRef, CFRelease>;

platform/darwin/src/local_glyph_rasterizer.mm

@@ -0,0 +1,233 @@
+#include <mbgl/text/local_glyph_rasterizer.hpp>
+#include <mbgl/util/i18n.hpp>
+#include <mbgl/util/platform.hpp>
+
+#include <unordered_map>
+
+#import <Foundation/Foundation.h>
+#import <CoreText/CoreText.h>
+#import <ImageIO/ImageIO.h>
+
+#import "CFHandle.hpp"
+
+namespace mbgl {
+
+/*
+    Darwin implementation of LocalGlyphRasterizer:
+     Draws CJK glyphs using locally available fonts.
+
+    Mirrors GL JS implementation in that:
+     - Only CJK glyphs are drawn locally (because we can guess their metrics effectively)
+        * Render size/metrics determined experimentally by rendering a few different fonts
+     - Configuration is done at map creation time by setting a "font family"
+        * JS uses a CSS font-family, this uses kCTFontFamilyNameAttribute which has
+          somewhat different behavior.
+     - We use heuristics to extract a font-weight based on the incoming font stack
+
+    Further improvements are possible:
+     - If we could reliably extract glyph metrics, we wouldn't be limited to CJK glyphs
+     - We could push the font configuration down to individual style layers, which would
+        allow any current style to be reproducible using local fonts.
+     - Instead of just exposing "font family" as a configuration, we could expose a richer
+        CTFontDescriptor configuration option (although we'd have to override font size to
+        make sure it stayed at 24pt).
+     - Because Apple exposes glyph paths via `CTFontCreatePathForGlyph` we could potentially
+        render directly to SDF instead of going through TinySDF -- although it's not clear
+        how much of an improvement it would be.
+*/
+
+using CGColorSpaceHandle = CFHandle<CGColorSpaceRef, CGColorSpaceRef, CGColorSpaceRelease>;
+using CGContextHandle = CFHandle<CGContextRef, CGContextRef, CGContextRelease>;
+using CFStringRefHandle = CFHandle<CFStringRef, CFTypeRef, CFRelease>;
+using CFAttributedStringRefHandle = CFHandle<CFAttributedStringRef, CFTypeRef, CFRelease>;
+using CFDictionaryRefHandle = CFHandle<CFDictionaryRef, CFTypeRef, CFRelease>;
+using CTFontDescriptorRefHandle = CFHandle<CTFontDescriptorRef, CFTypeRef, CFRelease>;
+using CTLineRefHandle = CFHandle<CTLineRef, CFTypeRef, CFRelease>;
+
+class LocalGlyphRasterizer::Impl {
+public:
+    Impl(const optional<std::string> fontFamily_)
+        : fontFamily(fontFamily_)
+    {}
+
+    ~Impl() {
+        for (auto& pair : fontHandles) {
+            CFRelease(pair.second);
+        }
+    }
+
+
+    CTFontRef getFont(const FontStack& fontStack) {
+        if (!fontFamily) {
+            return NULL;
+        }
+
+        if (fontHandles.find(fontStack) == fontHandles.end()) {
+
+            NSDictionary* fontTraits = @{ (NSString *)kCTFontSymbolicTrait: [NSNumber numberWithFloat:getFontWeight(fontStack)] };
+
+            NSDictionary *fontAttributes = @{
+                (NSString *)kCTFontSizeAttribute: [NSNumber numberWithFloat:24.0],
+                (NSString *)kCTFontFamilyNameAttribute: [[NSString alloc] initWithCString:fontFamily->c_str() encoding:NSUTF8StringEncoding],
+                (NSString *)kCTFontTraitsAttribute: fontTraits
+                //(NSString *)kCTFontStyleNameAttribute: (getFontWeight(fontStack) > .3) ? @"Bold" : @"Regular"
+            };
+
+            CTFontDescriptorRefHandle descriptor(CTFontDescriptorCreateWithAttributes((CFDictionaryRef)fontAttributes));
+            CTFontRef font = CTFontCreateWithFontDescriptor(*descriptor, 0.0, NULL);
+            if (!font) {
+                throw std::runtime_error("CTFontCreateWithFontDescriptor failed");
+            }
+
+            fontHandles[fontStack] = font;
+        }
+        return fontHandles[fontStack];
+    }
+
+private:
+    float getFontWeight(const FontStack& fontStack) {
+        // Analog to logic in glyph_manager.js
+        // From NSFontDescriptor.h (macOS 10.11+) NSFontWeight*:
+        constexpr float light = -.4;
+        constexpr float regular = 0.0;
+        constexpr float medium = .23;
+        constexpr float bold = .4;
+
+        float fontWeight = regular;
+        for (auto font : fontStack) {
+            // Last font in the fontstack "wins"
+            std::string lowercaseFont = mbgl::platform::lowercase(font);
+            if (lowercaseFont.find("bold") != std::string::npos) {
+                fontWeight = bold;
+            } else if (lowercaseFont.find("medium") != std::string::npos) {
+                fontWeight = medium;
+            } else if (lowercaseFont.find("light") != std::string::npos) {
+                fontWeight = light;
+            }
+        }
+
+        return fontWeight;
+    }
+
+    std::unordered_map<FontStack, CTFontRef, FontStackHash> fontHandles;
+    optional<std::string> fontFamily;
+};
+
+LocalGlyphRasterizer::LocalGlyphRasterizer(const optional<std::string> fontFamily)
+    : impl(std::make_unique<Impl>(fontFamily))
+{}
+
+LocalGlyphRasterizer::~LocalGlyphRasterizer()
+{}
+
+bool LocalGlyphRasterizer::canRasterizeGlyph(const FontStack& fontStack, GlyphID glyphID) {
+    return util::i18n::allowsFixedWidthGlyphGeneration(glyphID) && impl->getFont(fontStack);
+}
+
+/*
+// TODO: In theory we should be able to transform user-coordinate bounding box and advance
+// values into pixel glyph metrics. This would remove the need to use fixed glyph metrics
+// (which will be slightly off depending on the font), and allow us to return non CJK glyphs
+// (which will have variable "advance" values).
+void extractGlyphMetrics(CTFontRef font, CTLineRef line) {
+    CFArrayRef glyphRuns = CTLineGetGlyphRuns(line);
+    CFIndex runCount = CFArrayGetCount(glyphRuns);
+    assert(runCount == 1);
+    CTRunRef run = (CTRunRef)CFArrayGetValueAtIndex(glyphRuns, 0);
+    CFIndex glyphCount = CTRunGetGlyphCount(run);
+    assert(glyphCount == 1);
+    const CGGlyph *glyphs = CTRunGetGlyphsPtr(run);
+
+    CGRect boundingRects[1];
+    boundingRects[0] = CGRectMake(0, 0, 0, 0);
+    CGSize advances[1];
+    advances[0] = CGSizeMake(0,0);
+    CGRect totalBoundingRect = CTFontGetBoundingRectsForGlyphs(font, kCTFontOrientationDefault, glyphs, boundingRects, 1);
+    double totalAdvance = CTFontGetAdvancesForGlyphs(font, kCTFontOrientationDefault, glyphs, advances, 1);
+
+    // Break in the debugger to see these values: translating from "user coordinates" to bitmap pixel coordinates
+    // should be OK, but a lot of glyphs seem to have empty bounding boxes...?
+    (void)totalBoundingRect;
+    (void)totalAdvance;
+}
+*/
+
+PremultipliedImage drawGlyphBitmap(GlyphID glyphID, CTFontRef font, Size size) {
+    PremultipliedImage rgbaBitmap(size);
+
+    CFStringRefHandle string(CFStringCreateWithCharacters(NULL, reinterpret_cast<UniChar*>(&glyphID), 1));
+
+    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 * size.width;
+
+    CGContextHandle context(CGBitmapContextCreate(
+        rgbaBitmap.data.get(),
+        size.width,
+        size.height,
+        bitsPerComponent,
+        bytesPerRow,
+        *colorSpace,
+        kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedLast));
+    if (!context) {
+        throw std::runtime_error("CGBitmapContextCreate failed");
+    }
+
+    CFStringRef keys[] = { kCTFontAttributeName };
+    CFTypeRef values[] = { font };
+
+    CFDictionaryRefHandle attributes(
+        CFDictionaryCreate(kCFAllocatorDefault, (const void**)&keys,
+            (const void**)&values, sizeof(keys) / sizeof(keys[0]),
+            &kCFTypeDictionaryKeyCallBacks,
+            &kCFTypeDictionaryValueCallBacks));
+
+    CFAttributedStringRefHandle attrString(CFAttributedStringCreate(kCFAllocatorDefault, *string, *attributes));
+
+    CTLineRefHandle line(CTLineCreateWithAttributedString(*attrString));
+
+    // For debugging only, doesn't get useful metrics yet
+    //extractGlyphMetrics(font, *line);
+
+    // Start drawing a little bit below the top of the bitmap
+    CGContextSetTextPosition(*context, 0.0, 5.0);
+    CTLineDraw(*line, *context);
+
+    return rgbaBitmap;
+}
+
+Glyph LocalGlyphRasterizer::rasterizeGlyph(const FontStack& fontStack, GlyphID glyphID) {
+    Glyph fixedMetrics;
+    CTFontRef font = impl->getFont(fontStack);
+    if (!font) {
+        return fixedMetrics;
+    }
+
+    fixedMetrics.id = glyphID;
+
+    Size size(35, 35);
+
+    fixedMetrics.metrics.width = size.width;
+    fixedMetrics.metrics.height = size.height;
+    fixedMetrics.metrics.left = 3;
+    fixedMetrics.metrics.top = -1;
+    fixedMetrics.metrics.advance = 24;
+
+    PremultipliedImage rgbaBitmap = drawGlyphBitmap(glyphID, font, size);
+
+    // Copy alpha values from RGBA bitmap into the AlphaImage output
+    fixedMetrics.bitmap = AlphaImage(size);
+    for (uint32_t i = 0; i < size.width * size.height; i++) {
+        fixedMetrics.bitmap.data[i] = rgbaBitmap.data[4 * i + 3];
+    }
+
+    return fixedMetrics;
+}
+
+} // namespace mbgl

platform/default/local_glyph_rasterizer.cpp

@@ -2,6 +2,15 @@
 
 namespace mbgl {
 
+class LocalGlyphRasterizer::Impl {
+};
+
+LocalGlyphRasterizer::LocalGlyphRasterizer(const optional<std::string>)
+{}
+
+LocalGlyphRasterizer::~LocalGlyphRasterizer()
+{}
+
 bool LocalGlyphRasterizer::canRasterizeGlyph(const FontStack&, GlyphID) {
     return false;
 }

platform/ios/config.cmake

@@ -28,11 +28,12 @@ macro(mbgl_platform_core)
         # Misc
         PRIVATE platform/darwin/mbgl/storage/reachability.h
         PRIVATE platform/darwin/mbgl/storage/reachability.m
+        PRIVATE platform/darwin/src/CFHandle.hpp
+        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
 
@@ -84,6 +85,7 @@ macro(mbgl_platform_core)
     target_link_libraries(mbgl-core
         PUBLIC "-lz"
         PUBLIC "-framework Foundation"
+        PUBLIC "-framework CoreText"
         PUBLIC "-framework CoreGraphics"
         PUBLIC "-framework OpenGLES"
         PUBLIC "-framework ImageIO"

platform/macos/config.cmake

@@ -14,11 +14,12 @@ macro(mbgl_platform_core)
         # Misc
         PRIVATE platform/darwin/mbgl/storage/reachability.h
         PRIVATE platform/darwin/mbgl/storage/reachability.m
+        PRIVATE platform/darwin/src/CFHandle.hpp
+        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
 
@@ -64,6 +65,7 @@ macro(mbgl_platform_core)
     target_link_libraries(mbgl-core
         PUBLIC "-lz"
         PUBLIC "-framework Foundation"
+        PUBLIC "-framework CoreText"
         PUBLIC "-framework CoreGraphics"
         PUBLIC "-framework OpenGL"
         PUBLIC "-framework ImageIO"