From 0588c50b0923653cd6a19895a34cebb6aa8d91e7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Minh=20Nguye=CC=82=CC=83n?= <mxn@1ec5.org>
Date: Thu, 19 Mar 2020 17:46:13 -0700
Subject: [ios, macos] Get glyph metrics from font

Get glyph metrics from the font in the process of drawing each glyph into a bitmap context. These metrics result in more accurate kerning and better aligned baselines than the previous hard-coded values.

Align iOS/macOS local glyph rasterization test fixture to Qt.
---
 platform/darwin/src/local_glyph_rasterizer.mm | 89 +++++++++++++++++----------
 1 file changed, 56 insertions(+), 33 deletions(-)

(limited to 'platform')

diff --git a/platform/darwin/src/local_glyph_rasterizer.mm b/platform/darwin/src/local_glyph_rasterizer.mm
index d34dbc1167..b324184ba1 100644
--- a/platform/darwin/src/local_glyph_rasterizer.mm
+++ b/platform/darwin/src/local_glyph_rasterizer.mm
@@ -148,11 +148,39 @@ bool LocalGlyphRasterizer::canRasterizeGlyph(const FontStack&, GlyphID glyphID)
     return util::i18n::allowsFixedWidthGlyphGeneration(glyphID) && impl->isEnabled();
 }
 
-PremultipliedImage drawGlyphBitmap(GlyphID glyphID, CTFontRef font, Size size) {
-    PremultipliedImage rgbaBitmap(size);
-    
+PremultipliedImage drawGlyphBitmap(GlyphID glyphID, CTFontRef font, GlyphMetrics& metrics) {
     CFStringRefHandle string(CFStringCreateWithCharacters(NULL, reinterpret_cast<UniChar*>(&glyphID), 1));
+    if (!string) {
+        throw std::runtime_error("Unable to create string from codepoint");
+    }
+
+    CFStringRef keys[] = { kCTFontAttributeName };
+    CFTypeRef values[] = { font };
 
+    CFDictionaryRefHandle attributes(
+        CFDictionaryCreate(kCFAllocatorDefault, (const void**)&keys,
+            (const void**)&values, sizeof(keys) / sizeof(keys[0]),
+            &kCFTypeDictionaryKeyCallBacks,
+            &kCFTypeDictionaryValueCallBacks));
+    if (!attributes) {
+        throw std::runtime_error("Unable to create attributed string attributes dictionary");
+    }
+
+    CFAttributedStringRefHandle attrString(CFAttributedStringCreate(kCFAllocatorDefault, *string, *attributes));
+    if (!attrString) {
+        throw std::runtime_error("Unable to create attributed string");
+    }
+    CTLineRefHandle line(CTLineCreateWithAttributedString(*attrString));
+    if (!line) {
+        throw std::runtime_error("Unable to create line from attributed string");
+    }
+    
+    Size size(35, 35);
+    metrics.width = size.width;
+    metrics.height = size.height;
+    
+    PremultipliedImage rgbaBitmap(size);
+    
     CGColorSpaceHandle colorSpace(CGColorSpaceCreateDeviceRGB());
     if (!colorSpace) {
         throw std::runtime_error("CGColorSpaceCreateDeviceRGB failed");
@@ -173,52 +201,47 @@ PremultipliedImage drawGlyphBitmap(GlyphID glyphID, CTFontRef font, Size size) {
     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));
     
-    // Start drawing a little bit below the top of the bitmap
-    CGContextSetTextPosition(*context, 0.0, 5.0);
+    CFArrayRef glyphRuns = CTLineGetGlyphRuns(*line);
+    CTRunRef glyphRun = (CTRunRef)CFArrayGetValueAtIndex(glyphRuns, 0);
+    CFRange wholeRunRange = CFRangeMake(0, CTRunGetGlyphCount(glyphRun));
+    CGSize advances[wholeRunRange.length];
+    CTRunGetAdvances(glyphRun, wholeRunRange, advances);
+    metrics.advance = std::round(advances[0].width);
+    
+    // Mimic glyph PBF metrics.
+    metrics.left = Glyph::borderSize;
+    metrics.top = -1;
+    
+    // Move the text upward to avoid clipping off descenders.
+    CGFloat descent;
+    CTRunGetTypographicBounds(glyphRun, wholeRunRange, NULL, &descent, NULL);
+    CGContextSetTextPosition(*context, 0.0, descent);
+    
     CTLineDraw(*line, *context);
     
     return rgbaBitmap;
 }
 
 Glyph LocalGlyphRasterizer::rasterizeGlyph(const FontStack& fontStack, GlyphID glyphID) {
-    Glyph fixedMetrics;
-    CTFontRef font = impl->createFont(fontStack);
+    Glyph manufacturedGlyph;
+    CTFontRefHandle font(impl->createFont(fontStack));
     if (!font) {
-        return fixedMetrics;
+        return manufacturedGlyph;
     }
     
-    fixedMetrics.id = glyphID;
+    manufacturedGlyph.id = glyphID;
 
-    Size size(35, 35);
+    PremultipliedImage rgbaBitmap = drawGlyphBitmap(glyphID, *font, manufacturedGlyph.metrics);
     
-    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);
-   
+    Size size(manufacturedGlyph.metrics.width, manufacturedGlyph.metrics.height);
     // Copy alpha values from RGBA bitmap into the AlphaImage output
-    fixedMetrics.bitmap = AlphaImage(size);
+    manufacturedGlyph.bitmap = AlphaImage(size);
     for (uint32_t i = 0; i < size.width * size.height; i++) {
-        fixedMetrics.bitmap.data[i] = rgbaBitmap.data[4 * i + 3];
+        manufacturedGlyph.bitmap.data[i] = rgbaBitmap.data[4 * i + 3];
     }
 
-    return fixedMetrics;
+    return manufacturedGlyph;
 }
 
 } // namespace mbgl
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