Reading and Writing Picture Data

This section provides examples of how you can read and write picture data for the purpose of converting it to PDF or another Quartz-compatible format. Some general strategies include the following:

• As you convert data, you may find that some PICTs don’t convert well. In these cases, you’ll want to first convert the PICT to a pixel picture first. See Avoiding PICT Wrappers for Bitmap Images.

• For PICTs that are wrappers for JPEG data, use the function CGImageCreateWithJPEGDataProvider for the JPEG data rather than working with the PICT.

• If your application uses predefined PICT files or resources that are drawn repeatedly, you can convert them into PDF and place them in the Resources folder inside the application bundle. See Converting QDPict Pictures Into PDF Documents.

• Use Quartz data providers to work with QDPict data. See Creating a QDPict Picture From Data in Memory and Creating a QDPict Picture From a PICT File.

• If you need to draw PICT data scaled, evaluate which type of scaling is best for your purposes. See Scaling QDPict Pictures.

QDPictRef MyCreateQDPictWithData (void *data, size_t size)

{

    QDPictRef picture = NULL;

    CGDataProviderRef provider =

    CGDataProviderCreateWithData (NULL, data, size, MyReleaseProc);// 1

    if (provider != NULL)

    {

        picture = QDPictCreateWithProvider (provider);// 2

        CFRelease (provider);

    }

    return picture;

}

void MyReleaseProc (void *info, const void *data, size_t size)// 3

{

    if (info != NULL) {

        /* release private information here */

    };

    if (data != NULL) {

        /* release picture data here */

    };

}

QDPictRef MyCreateQDPictWithFSRef (const FSRef *file)

{

    QDPictRef picture = NULL;

    CFURLRef url = CFURLCreateFromFSRef (NULL, file);

    if (url != NULL)

    {

        picture = QDPictCreateWithURL (url);

        CFRelease(url);

    }

    return picture;

}

void MyConvertQDPict (QDPictRef picture, CFURLRef url,

                        CFDictionaryRef dict)

{

    CGContextRef context = NULL;

    CGRect bounds = QDPictGetBounds (picture);

    bounds.origin.x = 0;

    bounds.origin.y = 0;

    context = CGPDFContextCreateWithURL (url, &bounds, dict);// 1

    if (context != NULL)

    {

        CGContextBeginPage (context, &bounds);// 2

        (void) QDPictDrawToCGContext (context, bounds, picture);// 3

        CGContextEndPage (context);// 4

        CGContextRelease (context);// 5

    }

}

Scaling QDPict Pictures

When drawing a picture in a Quartz context, you have two ways to change the horizontal or vertical scale of the picture:

• Create a drawing rectangle by applying the change of scale to the bounds rectangle returned by QDPictGetBounds and pass this drawing rectangle to QDPictDrawToCGContext. When the picture is rendered, patterns are not scaled along with other graphic elements. This is the same behavior as that of the DrawPicture function. For example, compare the original picture in Figure 4-1 with the scaled picture in Figure 4-2.

• Before drawing the picture, apply the appropriate affine transformation—for example, by calling CGContextScaleCTM. When the picture is rendered, the entire picture is scaled, including patterns. The effect is equivalent to viewing the picture with the Preview application and clicking the Zoom In button. Compare the original in Figure 4-1 with the scaled picture in Figure 4-3 to see how this looks.

Listing 4-4 shows how to implement both types of scaling. A detailed explanation of each numbered line of code follows the listing.

Listing 4-4  A routine that uses two ways to scale a QDPict picture

void MyScaleQDPict (QDPictRef picture, CFURLRef url)

{

float scaleXY = 2.0;

CGRect bounds = QDPictGetBounds (picture);// 1

float w = (bounds.size.width) * scaleXY;

float h = (bounds.size.height) * scaleXY;

CGRect scaledBounds = CGRectMake (0, 0, w, h);

bounds.origin.x = 0;

bounds.origin.y = 0;

CGContextRef context = CGPDFContextCreateWithURL (url, NULL, NULL);// 2

if (context != NULL)

{

/* page 1: scale without affecting patterns */

CGContextBeginPage (context, &scaledBounds);

(void) QDPictDrawToCGContext (context, scaledBounds, picture);// 3

CGContextEndPage (context);

/* page 2: scale everything */

CGContextBeginPage (context, &scaledBounds);

CGContextScaleCTM (context, scaleXY, scaleXY);// 4

(void) QDPictDrawToCGContext (context, bounds, picture);// 5

CGContextEndPage (context);

CGContextRelease (context);

}

}

Here’s what the code does:

1. Creates a Quartz rectangle that represents the origin and size of the picture in user space. The resolution is 72 units per inch and the origin is (0,0).

2. Creates a PDF context that renders into a file. The choice of PDF is arbitrary—you can draw QDPict pictures in any type of Quartz graphics context.

3. Draws the picture into a scaled drawing rectangle. Patterns are not scaled along with the other graphic elements in the picture.

4. Applies the scaling transform to the current transformation matrix (CTM) in the graphics context. This scaling affects all subsequent drawing.

5. Draws the picture into a drawing rectangle with the same dimensions. This time the picture is scaled by the CTM, including patterns.

Working With PICT Data on the Clipboard (Pasteboard)

In Mac OS X, the Clipboard supports a rich set of data formats, including PDF. Beginning in Mac OS X version 10.3 (Panther), Carbon applications can use the Pasteboard Manager to exchange PDF data using the Clipboard or any other pasteboard. The Pasteboard Manager provides a robust data transport mechanism for user interface services such as copying, cutting, pasting, and dragging data of various flavors, and for generic interprocess communication.

A pasteboard is a global resource that uses Core Foundation data types to exchange information. Data formats called flavors are specified using uniform type identifiers. Supported flavors include plain text, rich text, PICT, and PDF. For a more detailed description of pasteboards, see Pasteboard Manager Programming Guide. For more information about uniform type identifiers, see Uniform Type Identifiers Overview.

To draw a PDF version of a QuickDraw picture and copy the PDF data to the Clipboard using the Pasteboard Manager, you need to do the following:

1. Create a Quartz data consumer to transfer the rendered output from a PDF context into a CFData object for the Pasteboard Manager.

2. Create a PDF context using your data consumer, draw content in this context, and release the context.

3. Create a PasteboardRef representation of the Clipboard, clear the current contents, and write your PDF data to it.

Listing 4-5 shows how to implement this procedure. A detailed explanation of each numbered line of code follows the listing. (To simplify this listing, OSStatus result codes are cast to void. If you use this sample code in an actual application, you should remove the casts and add the necessary error handling.)

Listing 4-5  Code that pastes the PDF representation of a picture to the Clipboard

size_t MyPutBytes (void* info, const void* buffer, size_t count)// 1

{

    CFDataAppendBytes ((CFMutableDataRef) info, buffer, count);

    return count;

}

void MyCopyQDPictToClipboard (QDPictRef picture)

{

    static CGDataConsumerCallbacks callbacks = { MyPutBytes, NULL };

    CFDataRef data = CFDataCreateMutable (kCFAllocatorDefault, 0);// 2

    if (data != NULL)

    {

        CGDataConsumerRef consumer = NULL;

        consumer = CGDataConsumerCreate ((void*) data, &callbacks);// 3

        if (consumer != NULL)

        {

            CGContextRef context = NULL;

            CGRect bounds = QDPictGetBounds (picture);

            bounds.origin.x = 0;

            bounds.origin.y = 0;

            context = CGPDFContextCreate (consumer, &bounds, NULL);// 4

            CGDataConsumerRelease (consumer);

            if (context != NULL)

            {

                /* convert PICT to PDF */

                CGContextBeginPage (context, &bounds);

                (void) QDPictDrawToCGContext (context, bounds, picture);// 5

                CGContextEndPage (context);

                CGContextRelease (context);// 6

                /* copy PDF to clipboard */

                PasteboardRef clipboard = NULL;

                (void) PasteboardCreate (kPasteboardClipboard, &clipboard);// 7

                (void) PasteboardClear (clipboard);// 8

                (void) PasteboardPutItemFlavor (clipboard, // 9

                        (PasteboardItemID) 1, kUTTypePDF,

                        data, kPasteboardFlavorNoFlags);

                CFRelease (clipboard);

            }

        }

    CFRelease (data); // You should ensure that data is not NULL.

    }

}

Here’s what the code does:

1. Implements a custom callback function to handle the PDF content stream coming from a Quartz PDF context. This function copies the PDF bytes from a Quartz-supplied buffer into a mutable CFDataRef object.

2. Creates a mutable CFDataRef object for the PDF data.

3. Creates a Quartz data consumer that uses the custom callback.

4. Creates a PDF context to draw the picture, using the data consumer.

5. Draws the QDPict picture in the PDF context.

6. Releases the PDF context, which “finalizes” the PDF data.

7. Creates an object of type PasteboardRef that serves as a data transport channel for a new or existing pasteboard—in this case, the Clipboard.

8. Clears the Clipboard of its current contents and makes it mutable.

9. Adds the PDF data to the Clipboard. Since there’s only one data item, the item identifier is 1. The uniform type identifier for PDF is declared in the interface file UTCoreTypes.h inside the Application Services framework.

Now that you’ve seen how to copy PICT data to the pasteboard, see Listing 4-6, which contains a routine that you can use to copy any Quartz drawing to the pasteboard. This routine is from the CarbonSketch sample application. The routine AddWindowContextToPasteboardAsPDF takes two parameters: a pasteboard reference and an application-defined data type that tracks various attributes of the drawing document, such as its size and content.

Listing 4-6  A routine that copies window content to the pasteboard (Clipboard)

static OSStatus AddWindowContentToPasteboardAsPDF (

                        PasteboardRef pasteboard, const DocStorage *docStP)

{

    OSStatus    err     = noErr;

    CGRect  docRect = CGRectMake (0, 0, docStP->docSize.h,

                                    docStP->docSize.v);

    CFDataRef       pdfData = CFDataCreateMutable (kCFAllocatorDefault, 0);

    CGContextRef            pdfContext;

    CGDataConsumerRef       consumer;

    CGDataConsumerCallbacks cfDataCallbacks = {MyCFDataPutBytes,

                                         MyCFDataRelease };

    err = PasteboardClear (pasteboard);// 1

    require_noerr err, PasteboardClear_FAILED);

    consumer = CGDataConsumerCreate ((void*)pdfData, &cfDataCallbacks);// 2

    pdfContext = CGPDFContextCreate (consumer, &docRect, NULL);// 3

    require(pdfContext != NULL, CGPDFContextCreate_FAILED);

    MyDrawIntoPDFPage (pdfContext, docRect, docStP, 1);// 4

    CGContextRelease (pdfContext);// 5

    err = PasteboardPutItemFlavor( pasteboard, (PasteboardItemID)1,// 6

                        kUTTypePDF, pdfData, kPasteboardFlavorNoFlags );

    require_noerr( err, PasteboardPutItemFlavor_FAILED );

CGPDFContextCreate_FAILED:

PasteboardPutItemFlavor_FAILED:

    CGDataConsumerRelease (consumer);   // 7

PasteboardClear_FAILED:

    return err;

}

Here’s what the code does:

1. Clears the pasteboard of its contents so that this application can own it and add its own data.

2. Creates a data consumer to receive the data from the application.

3. Creates a PDF graphics context, providing the data consumer, the rectangle that defines the size and location of the PDF page, and NULL for the auxiliary dictionary. The entire PDF page is supplied here, but in your application you restrict the data you paste to the contents of the selection made by the user. In this example, there isn’t any additional information to be used by the PDF context when generating the PDF, so the auxiliary dictionary is NULL.

4. Calls an application-defined function to draw the actual data into the PDF graphics context. You need to supply your own drawing function here.

5. Releases the PDF graphics context, which finalizes the PDF data.

6. Puts the PDF data (supplied by the data consumer) on the pasteboard. The PasteboardPutItemFlavor function takes the pasteboard cleared earlier, the identifier for the item to add flavor data for, a flavor type, the data to add, and a bit field of flags for the specified flavor.

7. Releases the data consumer.

Copying PDF Data From the Clipboard (Pasteboard)

To bring PDF data back into your application you retrieve the PDF data from the pasteboard, create a Quartz data provider that copies the PDF data into a Quartz buffer, and use the provider to create a CGPDFDocumentRef object. You can call CGContextDrawPDFDocument to draw the PDF version of your picture in any graphics context. The PasteboardContainsPDF routine in Listing 4-7 is taken from the CarbonSketch sample application.

The routine checks whether the pasteboard provided to it contains PDF data. If it does, the PDF data is returned as CFData in the pdfData parameter. A detailed explanation for each numbered line of code appears following the listing.

Listing 4-7  A routine that gets PDF data from the pasteboard (Clipboard)

static Boolean PasteboardContainsPDF (PasteboardRef inPasteboard,

                                 CFDataRef* pdfData)

{

    Boolean             gotPDF      = false;

    OSStatus            err         = noErr;

    ItemCount           itemCount;

    UInt32              itemIndex;

    err = PasteboardGetItemCount (inPasteboard, &itemCount);// 1

    require_noerr(err, PasteboardGetItemCount_FAILED);

    for (itemIndex = 1; itemIndex <= itemCount; ++itemIndex)// 2

    {

        PasteboardItemID    itemID;

        CFArrayRef          flavorTypeArray;

        CFIndex             flavorCount;

        CFIndex             flavorIndex;

        err = PasteboardGetItemIdentifier (inPasteboard, // 3

                            itemIndex, &itemID );

        require_noerr( err, PasteboardGetItemIdentifier_FAILED );

        err = PasteboardCopyItemFlavors (inPasteboard, itemID,// 4

                                 &flavorTypeArray );

        require_noerr( err, PasteboardCopyItemFlavors_FAILED );

        flavorCount = CFArrayGetCount( flavorTypeArray );// 5

        for (flavorIndex = 0; flavorIndex < flavorCount; ++flavorIndex)

        {

            CFStringRef             flavorType;

            CFComparisonResult      comparisonResult;

            flavorType = (CFStringRef)CFArrayGetValueAtIndex (// 6

                                         flavorTypeArray, flavorIndex );

            comparisonResult = CFStringCompare(flavorType,// 7

                                        kUTTypePDF, 0);

            if (comparisonResult == kCFCompareEqualTo)

            {

                if (pdfData != NULL)

                {

                    err = PasteboardCopyItemFlavorData( inPasteboard,// 8

                                 itemID, flavorType, pdfData );

                    require_noerr (err,

                            PasteboardCopyItemFlavorData_FAILED );

                }

                gotPDF = true;// 9

                break;

            }

PasteboardCopyItemFlavorData_FAILED:

PasteboardGetItemFlavorFlags_FAILED:

        }

        CFRelease(flavorTypeArray);// 10

PasteboardCopyItemFlavors_FAILED:

PasteboardGetItemIdentifier_FAILED:

        ;

    }

PasteboardGetItemCount_FAILED:

    return gotPDF;// 11

}

Here’s what that code does:

1. Gets the number of items on the pasteboard.

2. Iterates through each item on the pasteboard.

3. Gets the unique identifier for this pasteboard item.

4. Copies the flavor types for that item ID into an array. Note that the flavor type array is a CFArrayType that you need to release later.

5. Gets a count of the flavor types in the array. You need to iterate through these to find the PDF flavor.

6. Gets the flavor type stored in a specific location in the array.

7. Checks for the PDF flavor type. Note that in Mac OS X v10.4 you should use the universal type kUTTypePDF, as shown here, instead of CFSTR('com.adobe.pdf').

8. Copies the PDF data, if any is found.

9. Sets the gotPDF flag to true.

10. Releases the array.

11. Returns true if successful.

After you get the PDF data from the pasteboard, you can draw it in your application, using a routine similar to the DrawPDFData routine shown in Listing 4-8. The routine takes a CFDataRef data type (which is what you get from the routine in Listing 4-7 when you copy data from the pasteboard), a graphics context, and a destination rectangle. A detailed explanation for each numbered line of code appears following the listing.

Listing 4-8  A routine that draws PDF data

static void MyPDFDataRelease (void *info, const void *data, size_t size)

{

    if(info != NULL)

        CFRelease((CFDataRef)info);

}

static void DrawPDFData (CGContextRef ctx, CFDataRef pdfData,

                            CGRect dstRect)

{

    CGDataProviderRef   provider;

    CGPDFDocumentRef    document;

    CGPDFPageRef        page;

    CGRect              pageSize;

    CFRetain (pdfData);

    provider = CGDataProviderCreateWithData (pdfData, // 1

                        CFDataGetBytePtr(pdfData),

                        CFDataGetLength(pdfData), MyPDFDataRelease);

    document = CGPDFDocumentCreateWithProvider (provider);// 2

    CFRelease(provider);// 3

    page = CGPDFDocumentGetPage (document, 1);// 4

    pageSize = CGPDFPageGetBoxRect (page, kCGPDFMediaBox);// 5

    CGContextSaveGState(ctx);// 6

    MySetupTransform(ctx, pageSize, dstRect); // 7

// Scale pdf page into dstRect, if the pdf is too big

    CGContextDrawPDFPage (ctx, page);// 8

    CGContextRestoreGState(ctx);// 9

    CFRelease(document);// 10

}

Here’s what the code does:

1. Creates a data provider to read PDF data provided to your application from a CGDataRef data source. Note that you need to supply a release function for Quartz to call when it frees the data provider.

2. Creates a CGPDFDocument object using data supplied by the data provider you just created.

3. Releases the data provider. You should release a data provider immediately after using it to create the CGPDFDocument object.

4. Gets the first page of the newly created document.

5. Gets the media box rectangle for the PDF. You need this to determine how to scale the content later.

6. Saves the graphics state so that you can later restore it.

7. Calls an application-defined routine to set a transform, if necessary. This routine (which you would need to write) determines whether the PDF is too big to fit in the destination rectangle, and transforms the context appropriately.

8. Draws the PDF document into the graphics context that is passed to the DrawPDFData routine.

9. Restores the graphics state.

10. Releases the PDF document object.

Relevant Resources

See these reference documents:

• CGContext Reference

• CGImage Reference

• CGPDFDocument Reference

• Pasteboard Manager Reference

• QuickDraw Reference, describes the QDPictRef data type that represents a QuickDraw picture in the Quartz graphics environment.

For comprehensive information about using pasteboards in Carbon applications, see Pasteboard Manager Programming Guide.

For more information about uniform type identifiers, see the document Uniform Type Identifiers Overview.

To learn more about drawing QDPict pictures in a Carbon application, see the project example CGDrawPicture in the Graphics & Imaging Quartz Sample Code Library.