Uniface Demystified: Harnessing the Power of the image Data Type for Binary Data

For Uniface developers, managing diverse data types is a daily task. When it comes to handling non-textual information, particularly visual assets, the image data type stands out as a fundamental tool. While its name suggests a singular purpose, it’s far more versatile, serving as a robust container for any form of binary data within your applications.

Understanding the image Data Type’s Core Function

At its heart, the image data type in Uniface is designed to store raw binary sequences. This means it’s not limited to photographs or graphics; it can effectively hold anything from embedded icons and user interface elements to files loaded from local storage, and even proprietary binary outputs from external systems. Its primary applications include:

• Storing visual content directly within your database schemas.
• Managing graphical assets like glyphs and icons for UI consistency.
• Loading and processing image files (e.g., JPEG, PNG) from disk.
• Integrating binary data streams from various third-party filters or components.

Implementing the image Data Type in Your Code

Incorporating the image data type into your Uniface projects is straightforward. You declare image variables or parameters within the variables or params sections of your ProcScript blocks.

Consider this practical example where an image file is loaded into an image variable:

variables
  image lv_userProfilePic ; Declaring an image variable
endvariables

; ProcScript to populate the variable with an image from a specified path
read_image lv_userProfilePic, "C:\app_data\profile.jpg"

; The loaded image can now be assigned to a visual widget,
; displayed, or processed further within the application.
$widget("PROFILE_DISPLAY") = lv_userProfilePic

In this snippet, lv_userProfilePic becomes the memory holder for the binary data of profile.jpg, ready for display or manipulation.

Crucial Considerations When Working with image Data

To avoid common pitfalls and ensure your Uniface applications function reliably, keep these essential rules in mind:

1. No Arithmetic Operations: The image data type is not designed for mathematical computations. Attempting to apply arithmetic operators (like addition or subtraction) to image variables will result in errors, as these operations are semantically meaningless for binary data.

2. The Peril of Direct Image Comparison: This is perhaps the most critical point for developers. You absolutely cannot directly compare two image variables using standard equality operators (e.g., ==) to determine if their contents are identical. A direct comparison will always evaluate to true, regardless of whether the images actually differ, leading to silent and potentially significant logical errors in your application.

   For example, this seemingly logical comparison is fundamentally flawed:

   if (img_varA == img_varB)
     ; This block will always execute! Do NOT use this for content comparison.
   endif
   

   The Correct Approach: Hashing for Content Verification

   To reliably ascertain if two image variables hold identical binary content, you must leverage cryptographic hashing. A hash function generates a unique, fixed-size string (a “fingerprint”) for any given input data. If the hashes of two images match, their underlying binary content is identical.

   Here’s how you would correctly compare images using hashing:

   variables
     string lv_hashImage1, lv_hashImage2
     image lv_firstImage, lv_secondImage
   endvariables
   
   ; ... assume lv_firstImage and lv_secondImage are populated ...
   
   ; Compute SHA256 hashes for both images
   lv_hashImage1 = $$hash(lv_firstImage, "SHA256")
   lv_hashImage2 = $$hash(lv_secondImage, "SHA256")
   
   ; Now, compare the resulting hash strings
   if (lv_hashImage1 == lv_hashImage2)
     message "The binary content of both images is identical."
   else
     message "The images contain different binary data."
   endif
   

   By comparing the string representations of their hashes, you gain a robust and accurate method for determining image content equality.

Conclusion

The image data type is an indispensable asset in the Uniface developer’s toolkit for managing binary data. While powerful, understanding its nuances—especially regarding declaration, appropriate use cases, and the critical importance of hashing for content comparison—is key to building stable and effective Uniface applications. Embrace these best practices, and your journey with Uniface’s image data type will be a smooth one!