When minimum contrast is 0, don't break ligatures that have different background colors. Issue 5947

sources/NSArray+iTerm.h

@@ -17,6 +17,8 @@
 - (NSArray *)mapWithBlock:(id (^)(ObjectType anObject))block;
 - (NSArray *)flatMapWithBlock:(NSArray *(^)(ObjectType anObject))block;
+- (id)reduceWithBlock:(id (^)(ObjectType first, ObjectType second))block;
+
 // Returns those elements of the array for which block(element) returns YES.
 // block is called on every element in order.
 - (NSArray *)filteredArrayUsingBlock:(BOOL (^)(ObjectType anObject))block;

sources/iTermBackgroundColorRun.h

@@ -65,5 +65,8 @@ NS_INLINE BOOL iTermBackgroundColorRunsEqual(iTermBackgroundColorRun *a,
 @property(nonatomic, readonly) iTermBackgroundColorRun *valuePointer;
 @property(nonatomic, retain) NSColor *backgroundColor;
 @property(nonatomic, retain) NSColor *unprocessedBackgroundColor;
+
++ (instancetype)boxedBackgroundColorRunWithValue:(iTermBackgroundColorRun)value;
+
 @end

sources/iTermBackgroundColorRun.m

@@ -125,6 +125,14 @@ static void iTermMakeBackgroundColorRun(iTermBackgroundColorRun *run,
     iTermBackgroundColorRun _value;
 }
++ (instancetype)boxedBackgroundColorRunWithValue:(iTermBackgroundColorRun)value {
+    iTermBoxedBackgroundColorRun *run = [[[self alloc] init] autorelease];
+    if (run) {
+        run->_value = value;
+    }
+    return run;
+}
+
 - (void)dealloc {
     [_backgroundColor release];
     [_unprocessedBackgroundColor release];

sources/iTermTextDrawingHelper.m

@@ -388,27 +388,12 @@ typedef struct iTermTextColorContext {
     // Now iterate over the lines and paint the characters.
     CGContextRef ctx = (CGContextRef)[[NSGraphicsContext currentContext] graphicsPort];
-    iTermBackgroundColorRunsInLine *representativeRunArray = nil;
-    NSInteger count = 0;
-    for (iTermBackgroundColorRunsInLine *runArray in backgroundRunArrays) {
-        if (count == 0) {
-            representativeRunArray = runArray;
-            count = runArray.numberOfEquivalentRows;
-        }
-        count--;
-        [self drawCharactersForLine:runArray.line
-                                atY:runArray.y
-                     backgroundRuns:representativeRunArray.array
-                            context:ctx];
-        [self drawNoteRangesOnLine:runArray.line];
-
-        if (_debug) {
-            NSString *s = [NSString stringWithFormat:@"%d", runArray.line];
-            [s drawAtPoint:NSMakePoint(0, runArray.y)
-                withAttributes:@{ NSForegroundColorAttributeName: [NSColor blackColor],
-                                  NSBackgroundColorAttributeName: [NSColor whiteColor],
-                                  NSFontAttributeName: [NSFont systemFontOfSize:8] }];
-        }
+    if (self.minimumContrast > 0) {
+        [self drawForegroundForBackgroundRunArrays:backgroundRunArrays
+                                               ctx:ctx];
+    } else {
+        [self drawNoMinimumContrastContrastForegroundWithBackgroundRunArrays:backgroundRunArrays
+                                                                         ctx:ctx];
     }
     [self drawTopMargin];
@@ -940,6 +925,82 @@ typedef struct iTermTextColorContext {
     }
 }
+#pragma mark - Drawing: Foreground
+
+// Draw assuming no minimum contrast. Keeps glyphs together in a single background color run across different background colors.
+- (void)drawNoMinimumContrastContrastForegroundWithBackgroundRunArrays:(NSArray<iTermBackgroundColorRunsInLine *> *)backgroundRunArrays
+                                                                   ctx:(CGContextRef)ctx {
+    // Combine runs on each line, except those with different values of
+    // `selected` or `match`. Those properties affect foreground color and must
+    // split ligatures up.
+    NSArray<iTermBackgroundColorRunsInLine *> *fakeRunArrays = [backgroundRunArrays mapWithBlock:^id(iTermBackgroundColorRunsInLine *runs) {
+        NSMutableArray<iTermBoxedBackgroundColorRun *> *combinedRuns = [NSMutableArray array];
+        iTermBackgroundColorRun previousRun = { {0} };
+        BOOL havePreviousRun = NO;
+        for (iTermBoxedBackgroundColorRun *run in runs.array) {
+            if (!havePreviousRun) {
+                havePreviousRun = YES;
+                previousRun = *run.valuePointer;
+            } else if (run.valuePointer->selected == previousRun.selected &&
+                       run.valuePointer->isMatch == previousRun.isMatch) {
+                previousRun.range = NSUnionRange(previousRun.range, run.valuePointer->range);
+            } else {
+                [combinedRuns addObject:[iTermBoxedBackgroundColorRun boxedBackgroundColorRunWithValue:previousRun]];
+                previousRun = *run.valuePointer;
+            }
+        }
+        if (havePreviousRun) {
+            [combinedRuns addObject:[iTermBoxedBackgroundColorRun boxedBackgroundColorRunWithValue:previousRun]];
+        }
+
+        iTermBackgroundColorRunsInLine *fakeRuns = [[[iTermBackgroundColorRunsInLine alloc] init] autorelease];
+        fakeRuns.line = runs.line;
+        fakeRuns.y = runs.y;
+        fakeRuns.numberOfEquivalentRows = fakeRuns.numberOfEquivalentRows;
+        fakeRuns.array = combinedRuns;
+        return fakeRuns;
+    }];
+    [self drawForegroundForBackgroundRunArrays:fakeRunArrays
+                                           ctx:ctx];
+}
+
+// Draws 
+- (void)drawForegroundForBackgroundRunArrays:(NSArray<iTermBackgroundColorRunsInLine *> *)backgroundRunArrays
+                                         ctx:(CGContextRef)ctx {
+    iTermBackgroundColorRunsInLine *representativeRunArray = nil;
+    NSInteger count = 0;
+    for (iTermBackgroundColorRunsInLine *runArray in backgroundRunArrays) {
+        if (count == 0) {
+            representativeRunArray = runArray;
+            count = runArray.numberOfEquivalentRows;
+        }
+        count--;
+        [self drawForegroundForLineNumber:runArray.line
+                                        y:runArray.y
+                           backgroundRuns:representativeRunArray.array
+                                  context:ctx];
+    }
+}
+
+- (void)drawForegroundForLineNumber:(int)line
+                                  y:(CGFloat)y
+                     backgroundRuns:(NSArray<iTermBoxedBackgroundColorRun *> *)backgroundRuns
+                            context:(CGContextRef)ctx {
+    [self drawCharactersForLine:line
+                            atY:y
+                 backgroundRuns:backgroundRuns
+                        context:ctx];
+    [self drawNoteRangesOnLine:line];
+
+    if (_debug) {
+        NSString *s = [NSString stringWithFormat:@"%d", line];
+        [s drawAtPoint:NSMakePoint(0, y)
+        withAttributes:@{ NSForegroundColorAttributeName: [NSColor blackColor],
+                          NSBackgroundColorAttributeName: [NSColor whiteColor],
+                          NSFontAttributeName: [NSFont systemFontOfSize:8] }];
+    }
+}
+
 #pragma mark - Drawing: Text
 - (void)drawCharactersForLine:(int)line