Refactory thumbnail decoding, use a transformed CGContext instead of full context and re-scale after decode finished

This can help to avoid memory allocation

For encoding, avoid using vImageConvert_AnyToAny and just use it convenience method instead

Author: dreampiggy

SDWebImageWebPCoder/Classes/SDImageWebPCoder.m

@@ -68,12 +68,24 @@
 #endif
 #endif
 
-static inline CGImageRef __nullable CGBitmapContextCreateScaledImage(cg_nullable CGContextRef canvas, CGSize scaledSize) CF_RETURNS_RETAINED {
-    if (!canvas) return NULL;
-    CGContextSaveGState(canvas);
-    CGContextScaleCTM(canvas, scaledSize.width, scaledSize.height);
-    CGContextRestoreGState(canvas);
-    return CGBitmapContextCreateImage(canvas);
+/// Used for animated WebP, which need a canvas for decoding (rendering), possible apply a scale transform for thumbnail decoding (avoiding post-rescale using vImage)
+/// See more in #73
+static inline CGContextRef _Nullable CreateWebPCanvas(BOOL hasAlpha, CGSize canvasSize, CGSize thumbnailSize, BOOL preserveAspectRatio) {
+    CGBitmapInfo bitmapInfo = kCGBitmapByteOrder32Host;
+    bitmapInfo |= hasAlpha ? kCGImageAlphaPremultipliedFirst : kCGImageAlphaNoneSkipFirst;
+    // Check whether we need to use thumbnail
+    CGSize scaledSize = [SDImageCoderHelper scaledSizeWithImageSize:CGSizeMake(canvasSize.width, canvasSize.height) scaleSize:thumbnailSize preserveAspectRatio:preserveAspectRatio shouldScaleUp:NO];
+    CGContextRef canvas = CGBitmapContextCreate(NULL, scaledSize.width, scaledSize.height, 8, 0, [SDImageCoderHelper colorSpaceGetDeviceRGB], bitmapInfo);
+    if (!canvas) {
+        return nil;
+    }
+    // Check whether we need to use thumbnail
+    if (!CGSizeEqualToSize(canvasSize, scaledSize)) {
+        CGFloat sx = scaledSize.width / canvasSize.width;
+        CGFloat sy = scaledSize.height / canvasSize.height;
+        CGContextScaleCTM(canvas, sx, sy);
+    }
+    return canvas;
 }
 
 @interface SDWebPCoderFrame : NSObject
@@ -226,9 +238,7 @@ - (UIImage *)decodedImageWithData:(NSData *)data options:(nullable SDImageCoderO
     }
 
     BOOL hasAlpha = flags & ALPHA_FLAG;
-    CGBitmapInfo bitmapInfo = kCGBitmapByteOrder32Host;
-    bitmapInfo |= hasAlpha ? kCGImageAlphaPremultipliedFirst : kCGImageAlphaNoneSkipFirst;
-    CGContextRef canvas = CGBitmapContextCreate(NULL, canvasWidth, canvasHeight, 8, 0, [SDImageCoderHelper colorSpaceGetDeviceRGB], bitmapInfo);
+    CGContextRef canvas = CreateWebPCanvas(hasAlpha, CGSizeMake(canvasWidth, canvasHeight), thumbnailSize, preserveAspectRatio);
     if (!canvas) {
         WebPDemuxDelete(demuxer);
         CGColorSpaceRelease(colorSpace);
@@ -240,7 +250,7 @@ - (UIImage *)decodedImageWithData:(NSData *)data options:(nullable SDImageCoderO
 
     do {
         @autoreleasepool {
-            CGImageRef imageRef = [self sd_drawnWebpImageWithCanvas:canvas iterator:iter colorSpace:colorSpace scaledSize:scaledSize];
+            CGImageRef imageRef = [self sd_drawnWebpImageWithCanvas:canvas demuxer:demuxer iterator:iter colorSpace:colorSpace];
             if (!imageRef) {
                 continue;
             }
@@ -389,22 +399,15 @@ - (UIImage *)incrementalDecodedImageWithOptions:(SDImageCoderOptions *)options {
             return nil;
         }
 
-        CGContextRef canvas = CGBitmapContextCreate(NULL, width, height, 8, 0, [SDImageCoderHelper colorSpaceGetDeviceRGB], bitmapInfo);
+        CGContextRef canvas = CreateWebPCanvas(YES, CGSizeMake(width, height), _thumbnailSize, _preserveAspectRatio);
         if (!canvas) {
             CGImageRelease(imageRef);
             return nil;
         }
 
         // Only draw the last_y image height, keep remains transparent, in Core Graphics coordinate system
         CGContextDrawImage(canvas, CGRectMake(0, height - last_y, width, last_y), imageRef);
-        // Check whether we need to use thumbnail
-        CGImageRef newImageRef;
-        CGSize scaledSize = [SDImageCoderHelper scaledSizeWithImageSize:CGSizeMake(width, height) scaleSize:_thumbnailSize preserveAspectRatio:_preserveAspectRatio shouldScaleUp:NO];
-        if (!CGSizeEqualToSize(CGSizeMake(width, height), scaledSize)) {
-            newImageRef = CGBitmapContextCreateScaledImage(canvas, scaledSize);
-        } else {
-            newImageRef = CGBitmapContextCreateImage(canvas);
-        }
+        CGImageRef newImageRef = CGBitmapContextCreateImage(canvas);
         CGImageRelease(imageRef);
         if (!newImageRef) {
             CGContextRelease(canvas);
@@ -433,8 +436,8 @@ - (UIImage *)incrementalDecodedImageWithOptions:(SDImageCoderOptions *)options {
     return image;
 }
 
-- (void)sd_blendWebpImageWithCanvas:(CGContextRef)canvas iterator:(WebPIterator)iter colorSpace:(nonnull CGColorSpaceRef)colorSpaceRef {
-    size_t canvasHeight = CGBitmapContextGetHeight(canvas);
+- (void)sd_blendWebpImageWithCanvas:(CGContextRef)canvas demuxer:(nonnull WebPDemuxer *)demuxer iterator:(WebPIterator)iter colorSpace:(nonnull CGColorSpaceRef)colorSpaceRef {
+    int canvasHeight = WebPDemuxGetI(demuxer, WEBP_FF_CANVAS_HEIGHT);
     CGFloat tmpX = iter.x_offset;
     CGFloat tmpY = canvasHeight - iter.height - iter.y_offset;
     CGRect imageRect = CGRectMake(tmpX, tmpY, iter.width, iter.height);
@@ -456,14 +459,13 @@ - (void)sd_blendWebpImageWithCanvas:(CGContextRef)canvas iterator:(WebPIterator)
     }
 }
 
-- (nullable CGImageRef)sd_drawnWebpImageWithCanvas:(CGContextRef)canvas iterator:(WebPIterator)iter colorSpace:(nonnull CGColorSpaceRef)colorSpaceRef scaledSize:(CGSize)scaledSize CF_RETURNS_RETAINED {
+- (nullable CGImageRef)sd_drawnWebpImageWithCanvas:(CGContextRef)canvas demuxer:(nonnull WebPDemuxer *)demuxer iterator:(WebPIterator)iter colorSpace:(nonnull CGColorSpaceRef)colorSpaceRef CF_RETURNS_RETAINED {
     CGImageRef imageRef = [self sd_createWebpImageWithData:iter.fragment colorSpace:colorSpaceRef scaledSize:CGSizeZero];
     if (!imageRef) {
         return nil;
     }
 
-    size_t canvasWidth = CGBitmapContextGetWidth(canvas);
-    size_t canvasHeight = CGBitmapContextGetHeight(canvas);
+    int canvasHeight = WebPDemuxGetI(demuxer, WEBP_FF_CANVAS_HEIGHT);
     CGFloat tmpX = iter.x_offset;
     CGFloat tmpY = canvasHeight - iter.height - iter.y_offset;
     CGRect imageRect = CGRectMake(tmpX, tmpY, iter.width, iter.height);
@@ -474,17 +476,9 @@ - (nullable CGImageRef)sd_drawnWebpImageWithCanvas:(CGContextRef)canvas iterator
     if (!shouldBlend) {
         CGContextClearRect(canvas, imageRect);
     }
-    CGContextDrawImage(canvas, imageRect, imageRef);
-    
-    CGImageRef newImageRef;
-    // Check whether we need to use thumbnail
-    if (!CGSizeEqualToSize(CGSizeMake(canvasWidth, canvasHeight), scaledSize)) {
-        // Use CoreGraphics canvas to scale down, no need extra allocation
-        newImageRef = CGBitmapContextCreateScaledImage(canvas, scaledSize);
-    } else {
-        newImageRef = CGBitmapContextCreateImage(canvas);
-    }
 
+    CGContextDrawImage(canvas, imageRect, imageRef);
+    CGImageRef newImageRef = CGBitmapContextCreateImage(canvas);
     CGImageRelease(imageRef);
 
     if (iter.dispose_method == WEBP_MUX_DISPOSE_BACKGROUND) {
@@ -741,74 +735,22 @@ - (nullable NSData *)sd_encodedWebpDataWithImage:(nullable CGImageRef)imageRef
     if (!dataProvider) {
         return nil;
     }
-    // Check colorSpace is RGB/RGBA
-    CGColorSpaceRef colorSpace = CGImageGetColorSpace(imageRef);
-    BOOL isRGB = CGColorSpaceGetModel(colorSpace) == kCGColorSpaceModelRGB;
 
-    CFDataRef dataRef;
     uint8_t *rgba = NULL; // RGBA Buffer managed by CFData, don't call `free` on it, instead call `CFRelease` on `dataRef`
     // We could not assume that input CGImage's color mode is always RGB888/RGBA8888. Convert all other cases to target color mode using vImage
-    BOOL isRGB888 = isRGB && byteOrderNormal && alphaInfo == kCGImageAlphaNone && components == 3;
-    BOOL isRGBA8888 = isRGB && byteOrderNormal && alphaInfo == kCGImageAlphaLast && components == 4;
-    if (isRGB888 || isRGBA8888) {
-        // If the input CGImage is already RGB888/RGBA8888
-        dataRef = CGDataProviderCopyData(dataProvider);
-        if (!dataRef) {
-            return nil;
-        }
-        rgba = (uint8_t *)CFDataGetBytePtr(dataRef);
-    } else {
-        // Convert all other cases to target color mode using vImage
-        vImageConverterRef convertor = NULL;
-        vImage_Error error = kvImageNoError;
-        
-        vImage_CGImageFormat srcFormat = {
-            .bitsPerComponent = (uint32_t)bitsPerComponent,
-            .bitsPerPixel = (uint32_t)bitsPerPixel,
-            .colorSpace = colorSpace,
-            .bitmapInfo = bitmapInfo,
-            .renderingIntent = CGImageGetRenderingIntent(imageRef)
-        };
-        vImage_CGImageFormat destFormat = {
-            .bitsPerComponent = 8,
-            .bitsPerPixel = hasAlpha ? 32 : 24,
-            .colorSpace = [SDImageCoderHelper colorSpaceGetDeviceRGB],
-            .bitmapInfo = hasAlpha ? kCGImageAlphaLast | kCGBitmapByteOrderDefault : kCGImageAlphaNone | kCGBitmapByteOrderDefault // RGB888/RGBA8888 (Non-premultiplied to works for libwebp)
-        };
-        
-        convertor = vImageConverter_CreateWithCGImageFormat(&srcFormat, &destFormat, NULL, kvImageNoFlags, &error);
-        if (error != kvImageNoError) {
-            return nil;
-        }
-        
-        vImage_Buffer src;
-        error = vImageBuffer_InitWithCGImage(&src, &srcFormat, nil, imageRef, kvImageNoAllocate);
-        if (error != kvImageNoError) {
-            vImageConverter_Release(convertor);
-            return nil;
-        }
-        
-        vImage_Buffer dest;
-        error = vImageBuffer_Init(&dest, height, width, destFormat.bitsPerPixel, kvImageNoFlags);
-        if (error != kvImageNoError) {
-            vImageConverter_Release(convertor);
-            return nil;
-        }
-        
-        // Convert input color mode to RGB888/RGBA8888
-        error = vImageConvert_AnyToAny(convertor, &src, &dest, NULL, kvImageNoFlags);
-        
-        // Free the buffer
-        vImageConverter_Release(convertor);
-        if (error != kvImageNoError) {
-            free(dest.data);
-            return nil;
-        }
-        
-        rgba = dest.data; // Converted buffer
-        bytesPerRow = dest.rowBytes; // Converted bytePerRow
-        dataRef = CFDataCreateWithBytesNoCopy(kCFAllocatorDefault, rgba, bytesPerRow * height, kCFAllocatorDefault);
+    vImage_CGImageFormat destFormat = {
+        .bitsPerComponent = 8,
+        .bitsPerPixel = hasAlpha ? 32 : 24,
+        .colorSpace = [SDImageCoderHelper colorSpaceGetDeviceRGB],
+        .bitmapInfo = hasAlpha ? kCGImageAlphaLast | kCGBitmapByteOrderDefault : kCGImageAlphaNone | kCGBitmapByteOrderDefault // RGB888/RGBA8888 (Non-premultiplied to works for libwebp)
+    };
+    vImage_Buffer dest;
+    vImage_Error error = vImageBuffer_InitWithCGImage(&dest, &destFormat, NULL, imageRef, kvImageNoFlags);
+    if (error != kvImageNoError) {
+        return nil;
     }
+    rgba = dest.data;
+    bytesPerRow = dest.rowBytes;
 
     float qualityFactor = quality * 100; // WebP quality is 0-100
     // Encode RGB888/RGBA8888 buffer to WebP data
@@ -820,7 +762,8 @@ - (nullable NSData *)sd_encodedWebpDataWithImage:(nullable CGImageRef)imageRef
     if (!WebPConfigPreset(&config, WEBP_PRESET_DEFAULT, qualityFactor) ||
         !WebPPictureInit(&picture)) {
         // shouldn't happen, except if system installation is broken
-        CFRelease(dataRef);
+        free(dest.data);
+//        CFRelease(dataRef);
         return nil;
     }
 
@@ -840,7 +783,7 @@ - (nullable NSData *)sd_encodedWebpDataWithImage:(nullable CGImageRef)imageRef
     }
     if (!result) {
         WebPMemoryWriterClear(&writer);
-        CFRelease(dataRef);
+        free(dest.data);
         return nil;
     }
 
@@ -851,14 +794,14 @@ - (nullable NSData *)sd_encodedWebpDataWithImage:(nullable CGImageRef)imageRef
         if (!result) {
             WebPMemoryWriterClear(&writer);
             WebPPictureFree(&picture);
-            CFRelease(dataRef);
+            free(dest.data);
             return nil;
         }
     }
 
     result = WebPEncode(&config, &picture);
     WebPPictureFree(&picture);
-    CFRelease(dataRef); // Free bitmap buffer
+    free(dest.data);
 
     if (result) {
         // success
@@ -1140,16 +1083,13 @@ - (UIImage *)safeStaticImageFrame {
     if (_hasAnimation) {
         // If have animation, we still need to allocate a CGContext, because the poster frame may be smaller than canvas
         if (!_canvas) {
-            CGBitmapInfo bitmapInfo = kCGBitmapByteOrder32Host;
-            bitmapInfo |= _hasAlpha ? kCGImageAlphaPremultipliedFirst : kCGImageAlphaNoneSkipFirst;
-            CGContextRef canvas = CGBitmapContextCreate(NULL, _canvasWidth, _canvasHeight, 8, 0, [SDImageCoderHelper colorSpaceGetDeviceRGB], bitmapInfo);
+            CGContextRef canvas = CreateWebPCanvas(_hasAlpha, CGSizeMake(_canvasWidth, _canvasHeight), _thumbnailSize, _preserveAspectRatio);
             if (!canvas) {
                 return nil;
             }
             _canvas = canvas;
         }
-        CGSize scaledSize = [SDImageCoderHelper scaledSizeWithImageSize:CGSizeMake(_canvasWidth, _canvasHeight) scaleSize:_thumbnailSize preserveAspectRatio:_preserveAspectRatio shouldScaleUp:NO];
-        imageRef = [self sd_drawnWebpImageWithCanvas:_canvas iterator:iter colorSpace:_colorSpace scaledSize:scaledSize];
+        imageRef = [self sd_drawnWebpImageWithCanvas:_canvas demuxer:_demux iterator:iter colorSpace:_colorSpace];
     } else {
         CGSize scaledSize = [SDImageCoderHelper scaledSizeWithImageSize:CGSizeMake(iter.width, iter.height) scaleSize:_thumbnailSize preserveAspectRatio:_preserveAspectRatio shouldScaleUp:NO];
         imageRef = [self sd_createWebpImageWithData:iter.fragment colorSpace:_colorSpace scaledSize:scaledSize];
@@ -1169,9 +1109,7 @@ - (UIImage *)safeStaticImageFrame {
 
 - (UIImage *)safeAnimatedImageFrameAtIndex:(NSUInteger)index {
     if (!_canvas) {
-        CGBitmapInfo bitmapInfo = kCGBitmapByteOrder32Host;
-        bitmapInfo |= _hasAlpha ? kCGImageAlphaPremultipliedFirst : kCGImageAlphaNoneSkipFirst;
-        CGContextRef canvas = CGBitmapContextCreate(NULL, _canvasWidth, _canvasHeight, 8, 0, [SDImageCoderHelper colorSpaceGetDeviceRGB], bitmapInfo);
+        CGContextRef canvas = CreateWebPCanvas(_hasAlpha, CGSizeMake(_canvasWidth, _canvasHeight), _thumbnailSize, _preserveAspectRatio);
         if (!canvas) {
             return nil;
         }
@@ -1215,7 +1153,7 @@ - (UIImage *)safeAnimatedImageFrameAtIndex:(NSUInteger)index {
         if (endIndex > startIndex) {
             do {
                 @autoreleasepool {
-                    [self sd_blendWebpImageWithCanvas:_canvas iterator:iter colorSpace:_colorSpace];
+                    [self sd_blendWebpImageWithCanvas:_canvas demuxer:_demux iterator:iter colorSpace:_colorSpace];
                 }
             } while ((size_t)iter.frame_num < endIndex && WebPDemuxNextFrame(&iter));
         }
@@ -1228,9 +1166,7 @@ - (UIImage *)safeAnimatedImageFrameAtIndex:(NSUInteger)index {
     _currentBlendIndex = index;
 
     // Now the canvas is ready, which respects of dispose method behavior. Just do normal decoding and produce image.
-    // Check whether we need to use thumbnail
-    CGSize scaledSize = [SDImageCoderHelper scaledSizeWithImageSize:CGSizeMake(_canvasWidth, _canvasHeight) scaleSize:_thumbnailSize preserveAspectRatio:_preserveAspectRatio shouldScaleUp:NO];
-    CGImageRef imageRef = [self sd_drawnWebpImageWithCanvas:_canvas iterator:iter colorSpace:_colorSpace scaledSize:scaledSize];
+    CGImageRef imageRef = [self sd_drawnWebpImageWithCanvas:_canvas demuxer:_demux iterator:iter colorSpace:_colorSpace];
     if (!imageRef) {
         return nil;
     }