Introduction to Photoshop filter development--Photoshop callback function-PS Tutorial-php.cn

In the previous article, we introduced some of the most basic concepts and foundations for developing Photoshop filter plug-ins. Ps In order to meet the application needs of the plug-in, it also provides a large number of callback functions (or services) for the plug-in. For example, a filter can save the parameters set by the latest user after a call and apply them to the next call or display of the UI. This is done through the callback function of Ps. In this article we will explain some of the most important PS callback functions. After understanding this article, we will be able to use callback functions to complete the necessary work such as storing our filter parameters. This article will be much more complex and in-depth than the first one, but at the same time, from this article we can also get a glimpse of the internal secrets of PS: careful system design, perfect interface and complex working mechanism.

(1) Classification of callback functions:
The callback functions of PS can be divided into two types according to the location of obtaining them:
(1) Direct Callback: (can Directly called callback functions)
These callback functions are direct members of FilterRecord and can be obtained directly from the FilterRecord parameters. For example, AdvanceStateProc (update data), TestAbortProc (test user cancels), etc., fall into this category.
(2) CallBack Suite: (Receiving function set)
The recovery function set provided by the transfer function according to the function classification is a set of a set of callback functions. It is a pointer, which contains a set of sets The structure (struct) of the callback function, we can get a certain callback function set from FilterRecord, and then call the function in it.

The main callback function sets currently provided are:
Buffer Suite: Cache memory management (application and release of cache space).
UI Hook Suite: A set of functions related to UI operations.
Channel Ports Suite: Channel port reading and writing, used to read and write the real selection data inside PS! Rather than a copy copy.
Descriptor Suite: Descriptor operation set, used for script recording systems, which itself contains two sub-suites (sub-function sets): "read" and "write".
Color Space Suite: Color space services (color conversion, etc.).
Handle Suite: Handle management (PS encapsulated handle and memory management, similar to Buffer suite).
Error Suite: Receive and display error messages to users (receives different types of error message strings).
GetFileList Suite: Get the file list (get files, call the browser to browse the web, etc.).
GetPath Suite: Get the path.
ZString Suite: Encapsulates string processing.

For example, UI Hook Suite provides a set of callback functions related to UI. Its first version was defined as:

UI Hooks Suite Version1

# Please note that some callback functions are direct callbacks and are stored in a suite , such as testAbout and displayPixels. I speculate that in the early days, these function pointers were added to FilterRecord, but with the upgrade, more and more callback functions were added, which would cause FilterRecord to continuously upgrade and add members, making maintenance difficult, so Adobe began to add callback functions Classification is divided into several suites, and only the suite is placed in FilterRecord. In this way, when adding a function, you only need to add it to the corresponding suite and upgrade the suite without affecting the FilterRecord. In this way, some early callback functions are located in two places at the same time, FilterRecord and the suite to which they belong, so that they can be called directly or through the corresponding suite.

(2) Suite PEA (Plug-in function set management module (layer), my translated name, to be discussed) Suite PEA is a plug-in system used by some Adobe series software. It provides a common plug-in management core layer for the host program and a standard interface for plug-ins.
It is slightly different from the direct call in that the function set should be acquired (Acquired) before use, and the suite should be released (release) after use.

# );

Therefore, a function in the callback function set is called, in the following form:

Suite的获取和释放

# (3) Part of the more important callback function profile

This Here we will introduce some recovery functions that I think are more important for the filter plug -in . Briefly introduce the location and use of these callback functions.
3.1 DisplayPixelsProc( )
Function: Output pixel data (draw a picture) at the specified position on the specified DC. (Of course, we can actually complete this function ourselves.)
Location: Direct Callback, UI Hook Suite;
Definition:
OSErr (*DisplayPixelsProc) (const PSPixelMap *source ,
CONST VRECT *SRCRECT, Int32 DStrow, Int32 DStcol,
UNSIGNED32 PlatformContext);
## Source Instructions: Source: The first parameter is a structure that describes pixel information (PSPIXELMAP). pointer, which is defined as follows:

PSPixelMap Struct Define

PIDescriptorParameters Struct Define

Get the "read" and "write" sub-suite

##Code highlighting produced by Actipro CodeHighlighter (freeware)http:// www.php.cn/

Reading and writing parameter examples:
Reading parameters from the script system: Suppose the key of our parameter is 'Pam1', we use a temporary variable param1 to receive it:

Read A Parameter Demo Codeif (descParams->descriptor != NULL)
{
//Open the "read" descriptor
## 1 readProcs->openReadDescriptorProc(descParams->descriptor, array);        if
(token != NULL)
##
while(readProcs->
getKeyProc(token, &key, &type, &#flags) && !err)                                                                                                                                                 ##             case 'Pam1
'
:/ /
Read our parameters
##                                                                                                                                                    >getFloatProc(token, &param1);                                                              #default:                                                                                                                                                                                                     Since #

            err = readProcs->closeReadDescriptorProc(token);
            //释放描述符
            gFilterRecord->handleProcs->disposeProc(descParams->descriptor);
            descParams->descriptor = NULL;
        }
   }

向脚本系统写入参数：同上面的例子：

Write Descriptor Demo Code

3.3 DescriptorRegistry suite: (Descriptor registration function set)
The descriptor registration function set is mainly used for the registration and acquisition of descriptors. This allows ps to be entrusted to save our parameters while the filter is called multiple times. It contains several key functions for registration, removal, and key acquisition.
      Register()
                                                                                                                                                                                                                                                                         .
                                                                                                                # or descriptor, //Descriptor handle
Remove a Key Definition:
OSErr (*Erase)
(
) /* IN */ const char* key // Unique string or ID
);
##Get()
Description: Returns a Key. The returned descriptor is a copy, so you must actively release it after use.
                                                                                                                                                         /* OUT */ PIActionDescriptor* descriptor / / Release him after use );

3.4 ActionDescriptor suite: (Action descriptor function set)

## Action Descriptor function set, is used to store keys (or objects) into descriptors, read them from descriptors, and other descriptor management. This function set contains both read and write functions, and the usage method is similar to the descriptor in the previous section. It is defined as follows:

PSActionDescriptorProcs Struct

Code highlighting produced by Actipro CodeHighlighter (freeware)http:// www.php.cn/-->typedef
struct
PSActionDescriptorProcs {

Reading registered parameters//Get the descriptor of the specified ID
## err = registryProcs->Get(plugInUniqueID, &descriptor);
//Read registered Parameter err
= descriptorProcs->GetFloat(descriptor, 'Pam1',&param1);
//Release descriptor
if (descriptor != NULL ) descriptorProcs
->Free(descriptor);
//Release descriptor registration function set
##        if (registryProcs != NULL)                                                                                                                #->
ReleaseSuite(kPSDescriptorRegistrySuite,
##                                                                                                                                                                                                                       ##->
ReleaseSuite(kPSActionDescriptorSuite, ## (4) Summary
This article, we introduced some photoshop to the plug -in (not just to the filter plug -in) recovery function. It is divided into two major categories, one is directly included in the plug-in parameter structure, called a direct callback function; the other is a callback function included in the callback function set. For the direct callback function, the text only explains that DisplayPixelsProc can be used to map on the device DC. Including AdvanceStateProc, TestAbortProc, and UpdateProgressProc mentioned in the first article, they are all direct callbacks, and some direct callback functions belong to a certain Suite.          but also for the callback function set (Callback Suite), we focused on the reading, writing, registration and other operations in the Descriptor Suite in the callback function set. This function set can enable PS to record our filter parameters into the action sequence, or it can Register our filter parameters to save and read them across multiple calls. Other callback function sets such as memory management, color space services and other function sets have not been covered yet due to space limitations. (--By hoodlum1980)For more introduction to Photoshop filter development--Photoshop callback function related articles, please pay attention to the PHP Chinese website!