Calculate the DPI based on PDF mediaBox, support thumbnailPixelSize

Move the vector code from ImageIOAnimatedCoder to ImageIOCoder, since it's not animatable :)

SDWebImage/Core/SDImageIOAnimatedCoder.m

@@ -197,13 +197,6 @@ static NSString * kSDCGImageDestinationRequestedFileSize = @"kCGImageDestination
     if (!exifOrientation) {
         exifOrientation = kCGImagePropertyOrientationUp;
     }
-    
-    CFStringRef uttype = CGImageSourceGetType(source);
-    // Check vector format
-    BOOL isVector = NO;
-    if ([NSData sd_imageFormatFromUTType:uttype] == SDImageFormatPDF) {
-        isVector = YES;
-    }
 
     NSMutableDictionary *decodingOptions;
     if (options) {
@@ -214,11 +207,6 @@ static NSString * kSDCGImageDestinationRequestedFileSize = @"kCGImageDestination
     CGImageRef imageRef;
     BOOL createFullImage = thumbnailSize.width == 0 || thumbnailSize.height == 0 || pixelWidth == 0 || pixelHeight == 0 || (pixelWidth <= thumbnailSize.width && pixelHeight <= thumbnailSize.height);
     if (createFullImage) {
-        if (isVector) {
-            // Use 72 DPI by default, matching Apple's PDFKit behavior
-            NSUInteger rasterizationDPI = 72;
-            decodingOptions[kSDCGImageSourceRasterizationDPI] = @(rasterizationDPI);
-        }
         imageRef = CGImageSourceCreateImageAtIndex(source, index, (__bridge CFDictionaryRef)[decodingOptions copy]);
     } else {
         decodingOptions[(__bridge NSString *)kCGImageSourceCreateThumbnailWithTransform] = @(preserveAspectRatio);

SDWebImage/Core/SDImageIOCoder.m

@@ -13,6 +13,8 @@
 #import "UIImage+Metadata.h"
 #import "SDImageIOAnimatedCoderInternal.h"
 
+// Specify DPI for vector format in CGImageSource, like PDF
+static NSString * kSDCGImageSourceRasterizationDPI = @"kCGImageSourceRasterizationDPI";
 // Specify File Size for lossy format encoding, like JPEG
 static NSString * kSDCGImageDestinationRequestedFileSize = @"kCGImageDestinationRequestedFileSize";
 
@@ -52,6 +54,31 @@ static NSString * kSDCGImageDestinationRequestedFileSize = @"kCGImageDestination
     return coder;
 }
 
+#pragma mark - Utils
++ (CGRect)boxRectFromPDFFData:(nonnull NSData *)data {
+    CGDataProviderRef provider = CGDataProviderCreateWithCFData((__bridge CFDataRef)data);
+    if (!provider) {
+        return CGRectZero;
+    }
+    CGPDFDocumentRef document = CGPDFDocumentCreateWithProvider(provider);
+    CGDataProviderRelease(provider);
+    if (!document) {
+        return CGRectZero;
+    }
+    
+    // `CGPDFDocumentGetPage` page number is 1-indexed.
+    CGPDFPageRef page = CGPDFDocumentGetPage(document, 1);
+    if (!page) {
+        CGPDFDocumentRelease(document);
+        return CGRectZero;
+    }
+    
+    CGRect boxRect = CGPDFPageGetBoxRect(page, kCGPDFMediaBox);
+    CGPDFDocumentRelease(document);
+    
+    return boxRect;
+}
+
 #pragma mark - Decode
 - (BOOL)canDecodeFromData:(nullable NSData *)data {
     return YES;
@@ -88,13 +115,34 @@ static NSString * kSDCGImageDestinationRequestedFileSize = @"kCGImageDestination
         return nil;
     }
     
-    UIImage *image = [SDImageIOAnimatedCoder createFrameAtIndex:0 source:source scale:scale preserveAspectRatio:preserveAspectRatio thumbnailSize:thumbnailSize options:nil];
+    CFStringRef uttype = CGImageSourceGetType(source);
+    SDImageFormat imageFormat = [NSData sd_imageFormatFromUTType:uttype];
+    // Check vector format
+    NSDictionary *decodingOptions = nil;
+    if (imageFormat == SDImageFormatPDF) {
+        // Use 72 DPI (1:1 inch to pixel) by default, matching Apple's PDFKit behavior
+        NSUInteger rasterizationDPI = 72;
+        CGFloat maxPixelSize = MAX(thumbnailSize.width, thumbnailSize.height);
+        if (maxPixelSize > 0) {
+            // Calculate DPI based on PDF box and pixel size
+            CGRect boxRect = [self.class boxRectFromPDFFData:data];
+            CGFloat maxBoxSize = MAX(boxRect.size.width, boxRect.size.height);
+            if (maxBoxSize > 0) {
+                rasterizationDPI = rasterizationDPI * (maxPixelSize / maxBoxSize);
+            }
+        }
+        decodingOptions = @{
+            kSDCGImageSourceRasterizationDPI : @(rasterizationDPI),
+        };
+    }
+    
+    UIImage *image = [SDImageIOAnimatedCoder createFrameAtIndex:0 source:source scale:scale preserveAspectRatio:preserveAspectRatio thumbnailSize:thumbnailSize options:decodingOptions];
     CFRelease(source);
     if (!image) {
         return nil;
     }
     
-    image.sd_imageFormat = [NSData sd_imageFormatForImageData:data];
+    image.sd_imageFormat = imageFormat;
     return image;
 }
 

Tests/Tests/SDImageCoderTests.m

@@ -11,6 +11,12 @@
 #import "UIColor+SDHexString.h"
 #import <SDWebImageWebPCoder/SDWebImageWebPCoder.h>
 
+@interface SDImageIOCoder ()
+
++ (CGRect)boxRectFromPDFFData:(nonnull NSData *)data;
+
+@end
+
 @interface SDWebImageDecoderTests : SDTestCase
 
 @end
@@ -437,15 +443,14 @@ withLocalImageURL:(NSURL *)imageUrl
     CGFloat pixelHeight = inputImage.size.height;
     expect(pixelWidth).beGreaterThan(0);
     expect(pixelHeight).beGreaterThan(0);
-    // check vector format supports thumbnail with screen size
+    // check vector format should use 72 DPI
     if (isVector) {
-#if SD_UIKIT
-        CGFloat maxScreenSize = MAX(UIScreen.mainScreen.bounds.size.width, UIScreen.mainScreen.bounds.size.height);
-#else
-        CGFloat maxScreenSize = MAX(NSScreen.mainScreen.frame.size.width, NSScreen.mainScreen.frame.size.height);
-#endif
-        expect(pixelWidth).equal(maxScreenSize);
-        expect(pixelHeight).equal(maxScreenSize);
+        CGRect boxRect = [SDImageIOCoder boxRectFromPDFFData:inputImageData];
+        expect(boxRect.size.width).beGreaterThan(0);
+        expect(boxRect.size.height).beGreaterThan(0);
+        // Since 72 DPI is 1:1 from inch size to pixel size
+        expect(boxRect.size.width).equal(pixelWidth);
+        expect(boxRect.size.height).equal(pixelHeight);
     }
     
     // check thumbnail with scratch