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CIContext Class Reference

Inherits from
Conforms to
Framework
Library/Frameworks/QuartzCore.framework
Availability
Mac OS X v10.4 and later
Declared in
CIContext.h
Companion guides
Related sample code

Overview

The CIContext class provides an evaluation context for rendering a CIImage object through Quartz 2D or OpenGL. You use CIContext objects in conjunction with other Core Image classes, such as CIFilter, CIImage, and CIColor, to take advantage of the built-in Core Image filters when processing images.

Tasks

Creating a Context

Rendering Images

Managing Resources

Class Methods

contextWithCGContext:options:

Creates a Core Image context from a Quartz context, using the specified options.

+ (CIContext *)contextWithCGContext:(CGContextRef)ctx options:(NSDictionary *)dict

Parameters
ctx

A Quartz graphics context (CGContextRef object) either obtained from the system or created using a Quartz function such as CGBitmapContextCreate. See Quartz 2D Programming Guide for information on creating Quartz graphics contexts.

dict

A dictionary that contains color space information. You can provide the keys kCIContextOutputColorSpace or kCIContextWorkingColorSpace along with a CGColorSpaceRefobject for each color space.

Discussion

After calling this method, Core Image draws content to the specified Quartz graphics context.

When you create a CIContext object using a Quartz graphics context, any transformations that are already set on the Quartz graphics context affect drawing to that context.

Availability
See Also
Related Sample Code
Declared In
CIContext.h

contextWithCGLContext:pixelFormat:options:

Creates a Core Image context from a CGL context, using the specified options and pixel format object.

+ (CIContext *)contextWithCGLContext:(CGLContextObj)ctx pixelFormat:(CGLPixelFormatObj)pf options:(NSDictionary *)dict

Parameters
ctx

A CGL context (CGLContextObj object) obtain by calling the CGL function CGLCreateContext.

pf

A CGL pixel format object (CGLPixelFormatObj object) created by calling the CGL function CGLChoosePixelFormat. This argument must be the same pixel format object used to create the CGL context. The pixel format object must be valid for the lifetime of the Core Image context. Don’t release the pixel format object until after you release the Core Image context.

options

A dictionary that contains color space information. You can provide the keys kCIContextOutputColorSpace or kCIContextWorkingColorSpace along with a CGColorSpaceRef object for each color space.

Discussion

After calling this method, Core Image draws content into the surface (drawable object) attached to the CGL context. A CGL context is an Mac OS X OpenGL context. For more information, see OpenGL Programming Guide for Mac OS X.

When you create a CIContext object using a CGL context, all OpenGL states set for the CGL context affect rendering to that context. That means that coordinate and viewport transformations set on the CGL context as well as the vertex color.

For best results, follow these guidelines when you use Core Image to render into an OpenGL context:

Some typical initialization code for a view with width W and height H is:

    glViewport (0, 0, W, H);
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ();
    glOrtho (0, W, 0, H, -1, 1);
    glMatrixMode (GL_MODELVIEW);
    glLoadIdentity ();
    glBlendFunc (GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
    glEnable (GL_BLEND);
Availability
See Also
Related Sample Code
Declared In
CIContext.h

Instance Methods

clearCaches

Frees any cached data, such as temporary images, associated with the context and runs the garbage collector.

- (void)clearCaches

Discussion

You can use this method to remove textures from the texture cache that reference deleted images.

Availability
See Also
Declared In
CIContext.h

createCGImage:fromRect:

Creates a Quartz 2D image from a region of a CIImage object.

- (CGImageRef)createCGImage:(CIImage *)im fromRect:(CGRect)r

Parameters
im

A CIImage object.

r

The region of the image to render.

Return Value

A Quartz 2D (CGImageRef) image. You are responsible for releasing the returned image when you no longer need it.

Discussion

Renders a region of an image into a temporary buffer using the context, then creates and returns a Quartz 2D image with the results.

Availability
See Also
Related Sample Code
Declared In
CIContext.h

createCGImage:fromRect:format:colorSpace:

Creates a Quartz 2D image from a region of a CIImage object.

- (CGImageRef)createCGImage:(CIImage *)im fromRect:(CGRect)r format:(CIFormat)f colorSpace:(CGColorSpaceRef)cs

Parameters
im

A CIImage object.

r

The region of the image to render.

f

The format of the image.

cs

The color space of the image.

Return Value

A Quartz 2D (CGImageRef) image. You are responsible for releasing the returned image when you no longer need it.

Discussion

Renders a region of an image into a temporary buffer using the context, then creates and returns a Quartz 2D image with the results.

Availability
See Also
Declared In
CIContext.h

createCGLayerWithSize:info:

Creates a CGLayer object from the provided parameters.

- (CGLayerRef)createCGLayerWithSize:(CGSize)size info:(CFDictionaryRef)d

Parameters
size

The size, in default user space units, of the layer relative to the graphics context.

d

A dictionary, which is passed to CGLayerCreateWithContext as the auxiliaryInfo parameter. Pass NULL as this parameter is reserved for future use.

Return Value

A CGLayer (CGLayerRef) object.

Discussion

After calling this method, Core Image draws content into the CGLayer object. Core Image creates a CGLayer object by calling the Quartz 2D function CGLayerCreateWithContext, whose prototype is:

CGLayerRef CGLayerCreateWithContext (
   CGContextRef context,
   CGSize size,
   CFDictionaryRef auxiliaryInfo
);

Core Image passes the CIContext object as the context parameter, the size as the size parameter, and the dictionary as the auxiliaryInfo parameter. For more information on CGLayer objects, see Quartz 2D Programming Guide and CGLayer Reference.

Availability
See Also
Related Sample Code
Declared In
CIContext.h

drawImage:atPoint:fromRect:

Renders a region of an image to a point in the context destination.

- (void)drawImage:(CIImage *)im atPoint:(CGPoint)p fromRect:(CGRect)src

Parameters
im

A CIImage object.

p

The point in the context destination to draw to.

src

The region of the image to draw.

Discussion

You can call this method to force evaluation of the result after you apply a filter using one of the methods of the CIFilter class, such as apply:, apply:arguments:options:, and apply:k, . . ..

Availability
See Also
Related Sample Code
Declared In
CIContext.h

drawImage:inRect:fromRect:

Renders a region of an image to a rectangle in the context destination.

- (void)drawImage:(CIImage *)im inRect:(CGRect)dest fromRect:(CGRect)src

Parameters
im

A CIImage object.

dest

The rectangle in the context destination to draw into.

src

The subregion of the image that you want to draw into the context, with the origin and target size defined by the dest parameter.

Discussion

You can call this method to force evaluation of the result after you you apply a filter using one of the methods of the CIFilter class, such as apply:, apply:arguments:options:, and apply:k, . . ..

Availability
See Also
Related Sample Code
Declared In
CIContext.h

reclaimResources

Runs the garbage collector to reclaim any resources that the context no longer requires.

- (void)reclaimResources

Discussion

The system calls this method automatically after every rendering operation. You can use this method to remove textures from the texture cache that reference deleted images.

Availability
See Also
Declared In
CIContext.h

render:toBitmap:rowBytes:bounds:format:colorSpace:

Renders to the given bitmap.

- (void)render:(CIImage *)im toBitmap:(void *)data rowBytes:(ptrdiff_t)rb bounds:(CGRect)r format:(CIFormat)f colorSpace:(CGColorSpaceRef)cs

Parameters
im

A CIImage object.

data

Storage for the bitmap data.

rb

The bytes per row.

r

The bounds of the bitmap data.

f

The format of the bitmap data.

cs

The color space for the data. Pass NULL if you want to use the output color space of the context.

Availability
Declared In
CIContext.h

Constants

Context Options

Keys in the options dictionary for a CIContext object.

extern NSString *kCIContextOutputColorSpace;
extern NSString *kCIContextWorkingColorSpace;
extern NSString *kCIContextUseSoftwareRenderer;

Constants
kCIContextOutputColorSpace

A key for the color space to use for images before they are rendered to the context. By default, Core Image uses the GenericRGB color space, which leaves color matching to the system. You can specify a different output color space by providing a Quartz 2D CGColorSpace object (CGColorSpaceRef). (See Quartz 2D Programming Guide for information on creating and using CGColorSpace objects.)

kCIContextWorkingColorSpace

A key for the color space to use for image operations. By default, Core Image assumes that processing nodes are 128 bits-per-pixel, linear light, premultiplied RGBA floating-point values that use the GenericRGB color space. You can specify a different working color space by providing a Quartz 2D CGColorSpace object (CGColorSpaceRef). Note that the working color space must be RGB-based. If you have YUV data as input (or other data that is not RGB-based), you can use ColorSync functions to convert to the working color space. (See Quartz 2D Programming Guide for information on creating and using CGColorSpace objects.)

kCIContextUseSoftwareRenderer

A key for enabling software renderer use. If the associated NSNumber object is YES, then the software renderer is required.

Declared In
CIContext.h

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© 2007 Apple Inc. All Rights Reserved. (Last updated: 2007-03-16)

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