Question

我正在尝试访问用PDF写入的CGContext像素，但位图缓冲区似乎没有更新。任何帮助将不胜感激：

//Get the reference to our current page
pageRef = CGPDFDocumentGetPage(docRef, iCurrentPage);
//Start with a media crop, but see if we can shrink to smaller crop
CGRect pdfRect1 = CGRectIntegral(CGPDFPageGetBoxRect(pageRef, kCGPDFMediaBox));
CGRect r1 = CGRectIntegral(CGPDFPageGetBoxRect(pageRef, kCGPDFCropBox));
if (!CGRectIsEmpty(r1))
    pdfRect1 = r1;


    int wide = pdfRect1.size.width + pdfRect1.origin.x;
    int high = pdfRect1.size.height + pdfRect1.origin.y;    

    CGContextRef ctxBuffer = NULL;
    CGColorSpaceRef colorSpace;
    UInt8* bitmapData;
    int bitmapByteCount;
    int bitmapBytesPerRow;
    bitmapBytesPerRow = (wide * 4); 
    bitmapByteCount = (bitmapBytesPerRow * high);
    colorSpace = CGColorSpaceCreateDeviceRGB();
    bitmapData = malloc( bitmapByteCount );
    if (bitmapData == NULL)
    {
        DebugLog (@"Memory not allocated!");
        return;
    }
    ctxBuffer = CGBitmapContextCreate (bitmapData, 
                                     wide,
                                     high,
                                     8, // bits per component
                                     bitmapBytesPerRow,
                                     colorSpace,
                                     kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big); //
    if (ctxBuffer== NULL)
    {
        free (bitmapData); 
        DebugLog (@"Context not created!");
        return;
    }
    CGColorSpaceRelease( colorSpace ); 


    //White out the current context
    CGContextSetRGBFillColor(ctxBuffer, 1.0, 1.0, 1.0, 1.0);
    CGContextFillRect(ctxBuffer, CGContextGetClipBoundingBox(ctxBuffer));
    CGContextDrawPDFPage(ctxBuffer, pageRef);

//!!!This displays just fine to the context passed in from - (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx.  That is, I can see the PDf page rendered, so we know ctxBuffer was created correctly
//However, if I view bitmapData in memory, it only shows as 0xFF (or whatever fill color I use)
    CGImageRef img = CGBitmapContextCreateImage(ctxBuffer);     
    CGContextDrawImage(ctx, tiledLayer.frame, img); 


    for (int i = 0; i < wide; i++) 
    {

        for (int j = 0; j < high; j++) 
        {
            //All of the bytes show as 0xFF (or whatever fill color I test with)?!
            int byteIndex = (j * 4) + i * 4;
            UInt8 red = bitmapData[byteIndex];
            UInt8 green = bitmapData[byteIndex + 1];
            UInt8 blue = bitmapData[byteIndex + 2];
            UInt8 alpha = m_PixelBuf[byteIndex + 3];
        }           
    }

我也尝试过使用CGDataProviderCopyData(CGImageGetDataProvider(img))＆amp; CFDataGetBytePtr，但结果是一样的吗？

Answer 1

Bonehead奖励给我。循环索引不正确（j * 4）=＆gt; （j * bitmapBytesPerRow）

CGContextDrawPDFPage似乎不会在CGContext中持久存在

1 个答案: