Construct arbitrarily tall glyphs.

Fix the descent for glyphs in large operators. This fixes placement of limits
for the XITS font.

Fixes tophatmonocle#9.

iosMath/render/MTMathListDisplay.m

@@ -440,14 +440,16 @@ @implementation MTGlyphDisplay {
     MTFont* _font;
 }
 
-- (instancetype)initWithGlpyh:(CGGlyph) glyph  position:(CGPoint) position range:(NSRange) range font:(MTFont*) font
+@synthesize shiftDown;
+
+- (instancetype)initWithGlpyh:(CGGlyph) glyph range:(NSRange) range font:(MTFont*) font
 {
     self = [super init];
     if (self) {
         _font = font;
         _glyph = glyph;
 
-        self.position = position;
+        self.position = CGPointZero;
         self.range = range;
     }
     return self;
@@ -460,16 +462,87 @@ - (void)draw:(CGContextRef)context
     [self.textColor setFill];
 
     // Make the current position the origin as all the positions of the sub atoms are relative to the origin.
-    CGContextTranslateCTM(context, self.position.x, self.position.y);
+    CGContextTranslateCTM(context, self.position.x, self.position.y - self.shiftDown);
     CGContextSetTextPosition(context, 0, 0);
 
-    // Draw the glyph.
-    CGPoint glyphPosition = CGPointMake(0, -self.shiftDown);
-    CTFontDrawGlyphs(_font.ctFont, &_glyph, &glyphPosition, 1, context);
+    CTFontDrawGlyphs(_font.ctFont, &_glyph, &CGPointZero, 1, context);
 
     CGContextRestoreGState(context);
 }
 
+- (CGFloat)ascent
+{
+    return super.ascent - self.shiftDown;
+}
+
+- (CGFloat)descent
+{
+    return super.descent + self.shiftDown;
+}
+
+@end
+
+#pragma mark - MTGlyphConstructionDisplay
+
+@implementation MTGlyphConstructionDisplay {
+    CGGlyph *_glyphs;
+    CGPoint *_positions;
+    MTFont* _font;
+    int _numGlyphs;
+}
+
+@synthesize shiftDown;
+
+- (instancetype)initWithGlyphs:(NSArray<NSNumber *> *)glyphs offsets:(NSArray<NSNumber *> *)offsets font:(MTFont *)font
+{
+    self = [super init];
+    if (self) {
+        NSAssert(glyphs.count == offsets.count, @"Glyphs and offsets need to match");
+        _numGlyphs = glyphs.count;
+        _glyphs = malloc(sizeof(CGGlyph) * _numGlyphs);
+        _positions = malloc(sizeof(CGPoint) * _numGlyphs);
+        for (int i = 0; i < _numGlyphs; i++) {
+            _glyphs[i] = glyphs[i].shortValue;
+            _positions[i] = CGPointMake(0, offsets[i].floatValue);
+        }
+        _font = font;
+        self.position = CGPointZero;
+    }
+    return self;
+}
+
+- (void)draw:(CGContextRef)context
+{
+    CGContextSaveGState(context);
+
+    [self.textColor setFill];
+
+    // Make the current position the origin as all the positions of the sub atoms are relative to the origin.
+    CGContextTranslateCTM(context, self.position.x, self.position.y - self.shiftDown);
+    CGContextSetTextPosition(context, 0, 0);
+
+    // Draw the glyphs.
+    CTFontDrawGlyphs(_font.ctFont, _glyphs, _positions, _numGlyphs, context);
+
+    CGContextRestoreGState(context);
+}
+
+- (CGFloat)ascent
+{
+    return super.ascent - self.shiftDown;
+}
+
+- (CGFloat)descent
+{
+    return super.descent + self.shiftDown;
+}
+
+- (void)dealloc
+{
+    free(_glyphs);
+    free(_positions);
+}
+
 @end
 
 #pragma mark - MTLargeOpLimitsDisplay

iosMath/render/internal/MTFontMathTable.h

@@ -14,6 +14,27 @@
 
 @class MTFont;
 
+/** MTGlyphPart represents a part of a glyph used for assembling a large vertical or horizontal
+ glyph. */
+@interface MTGlyphPart : NSObject
+
+/// The glyph that represents this part
+@property (nonatomic, readonly) CGGlyph glyph;
+
+/// Full advance width/height for this part, in the direction of the extension in points.
+@property (nonatomic, readonly) CGFloat fullAdvance;
+
+/// Advance width/ height of the straight bar connector material at the beginning of the glyph in points.
+@property (nonatomic, readonly) CGFloat startConnectorLength;
+
+/// Advance width/ height of the straight bar connector material at the end of the glyph in points.
+@property (nonatomic, readonly) CGFloat endConnectorLength;
+
+/// If this part is an extender. If set, the part can be skipped or repeated.
+@property (nonatomic, readonly) BOOL isExtender;
+
+@end
+
 /** This class represents the Math table of an open type font.
  
  The math table is documented here: https://www.microsoft.com/typography/otspec/math.htm
@@ -135,4 +156,13 @@
  If there isn't any this returns -1. */
 - (CGFloat) getTopAccentAdjustment:(CGGlyph) glyph;
 
+#pragma mark Glyph Construction
+
+/** Minimum overlap of connecting glyphs during glyph construction */
+@property (nonatomic, readonly) CGFloat minConnectorOverlap;
+
+/** Returns an array of the glyph parts to be used for constructing vertical variants
+ of this glyph. If there is no glyph assembly defined, returns nil. */
+- (nullable NSArray<MTGlyphPart*>*) getVerticalGlyphAssemblyForGlyph:(CGGlyph) glyph;
+
 @end

iosMath/render/internal/MTFontMathTable.m

@@ -13,6 +13,21 @@
 #import "MTFont.h"
 #import "MTFont+Internal.h"
 
+
+@interface MTGlyphPart ()
+
+@property (nonatomic) CGGlyph glyph;
+@property (nonatomic) CGFloat fullAdvance;
+@property (nonatomic) CGFloat startConnectorLength;
+@property (nonatomic) CGFloat endConnectorLength;
+@property (nonatomic) BOOL isExtender;
+
+@end
+
+@implementation MTGlyphPart
+
+@end
+
 @interface MTFontMathTable ()
 
 // The font for this math table.
@@ -476,4 +491,47 @@ - (CGFloat) getTopAccentAdjustment:(CGGlyph) glyph
     }
 }
 
+#pragma mark - Glyph Assembly
+
+- (CGFloat)minConnectorOverlap
+{
+    return [self constantFromTable:@"MinConnectorOverlap"];
+}
+
+static NSString* const kVertAssembly = @"v_assembly";
+static NSString* const kAssemblyParts = @"parts";
+
+- (NSArray<MTGlyphPart *> *)getVerticalGlyphAssemblyForGlyph:(CGGlyph)glyph
+{
+    NSDictionary* assemblyTable = (NSDictionary*) _mathTable[kVertAssembly];
+    NSString* glyphName = [self.font getGlyphName:glyph];
+    NSDictionary* assemblyInfo = (NSDictionary*) assemblyTable[glyphName];
+    if (!assemblyInfo) {
+        // No vertical assembly defined for glyph
+        return nil;
+    }
+    NSArray* parts = (NSArray*) assemblyInfo[kAssemblyParts];
+    if (!parts) {
+        // parts should always have been defined, but if it isn't return nil
+        return nil;
+    }
+    NSMutableArray<MTGlyphPart*>* rv = [NSMutableArray array];
+    for (NSDictionary* partInfo in parts) {
+        MTGlyphPart* part = [[MTGlyphPart alloc] init];
+        NSNumber* adv = (NSNumber*) partInfo[@"advance"];
+        part.fullAdvance = [self fontUnitsToPt:adv.intValue];
+        NSNumber* end = (NSNumber*) partInfo[@"endConnector"];
+        part.endConnectorLength = [self fontUnitsToPt:end.intValue];
+        NSNumber* start = (NSNumber*) partInfo[@"startConnector"];
+        part.startConnectorLength = [self fontUnitsToPt:start.intValue];
+        NSNumber* ext = (NSNumber*) partInfo[@"extender"];
+        part.isExtender = ext.boolValue;
+        NSString* glyphName = (NSString*) partInfo[@"glyph"];
+        part.glyph = [self.font getGlyphWithName:glyphName];
+
+        [rv addObject:part];
+    }
+    return rv;
+}
+
 @end

iosMath/render/internal/MTMathListDisplayInternal.h

@@ -20,6 +20,13 @@
 
 @end
 
+// The Downshift protocol allows an MTDisplay to be shifted down by a given amount.
+@protocol DownShift <NSObject>
+
+@property (nonatomic) CGFloat shiftDown;
+
+@end
+
 @interface MTMathListDisplay ()
 
 - (instancetype)init NS_UNAVAILABLE;
@@ -64,12 +71,17 @@
 @end
 
 // Rendering of an large glyph as an MTDisplay
-@interface MTGlyphDisplay()
+@interface MTGlyphDisplay() <DownShift>
 
-- (instancetype)initWithGlpyh:(CGGlyph) glyph  position:(CGPoint) position range:(NSRange) range font:(MTFont*) font NS_DESIGNATED_INITIALIZER;
+- (instancetype)initWithGlpyh:(CGGlyph) glyph range:(NSRange) range font:(MTFont*) font NS_DESIGNATED_INITIALIZER;
 
-// Shift the glyph down by the given amount.
-@property (nonatomic) CGFloat shiftDown;
+@end
+
+// Rendering of a constructed glyph as an MTDisplay
+@interface MTGlyphConstructionDisplay : MTDisplay<DownShift>
+
+- (instancetype) init NS_UNAVAILABLE;
+- (instancetype) initWithGlyphs:(NSArray<NSNumber*>*) glyphs offsets:(NSArray<NSNumber*>*) offsets font:(MTFont*) font NS_DESIGNATED_INITIALIZER;
 
 @end