Java AWT Native Interface

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Java AWT Native Interface (JAWT) is an interface for the Java programming language that enables rendering libraries compiled to native code to draw directly to a Java Abstract Window Toolkit (AWT) Canvas object drawing surface.

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The Java Native Interface (JNI) allows developers to add platform-dependent functionality to Java applications. The JNI enables developers to add time-critical operations like mathematical calculations and 3D rendering.

Previously, native 3D rendering was challenging because the native code did not have access to the graphic context. The AWT Native Interface is designed to give developers access to an AWT Canvas for direct drawing with native code. In fact, the Java 3D API extension to the standard Java SE JDK relies heavily on the AWT Native Interface to render 3D objects in Java.

The AWT Native Interface is very similar to the JNI and the steps are the same as those of the JNI. See the Java Native Interface article for an explanation of the JNI techniques employed by the AWT Native Interface. The AWT Native Interface was added to the Java platform with the J2SE 1.3 ("Kestrel") version.

AWT Native Interface steps

A complete walkthrough example of this technology is available on Wikibooks (see link below).

A comprehensive example demonstrating this technology is available on Wikibooks (refer to the link below).

To begin, a Java application is created. The utilization of the Java Native Interface is explained in the article. The native keyword and the loadLibrary() method are integral components, while the paint() method is invoked when the AWT event dispatching thread repaints the screen.

Following the creation of the Java application, a C++ header file is generated conventionally. Detailed explanations can be found in the Java Native Interface documentation.

Next, the C++ native code is implemented, typically in a file named "NativeSideCanvas.cpp," and compiled into a library. Further information on this process is provided in the Java Native Interface (JNI) documentation.

Once the program is constructed, it can be executed as per usual. Upon running the file, a window should appear, displaying, for example, a drawn rectangle. Detailed instructions can be found in the Java Native Interface documentation.

It's important to note that the AWT Native Interface necessitates the presence of the "jawt.dll" (or "jawt.so") file to run alongside the application. The simplest method to ensure this is by copying the "jawt.dll" file, typically found in the .../jre/bin directory within the JDK's installation path.

Native painting

One can paint as if it is a native application. In Windows, the JVM will pass a HWND and other window information to the native application so that the application will "know" where to draw. It could use GDI to draw a Rectangle. The window information the native side needs will be in a JAWT_Win32DrawingSurfaceInfo structure (depending on Operating System) which can be retrieved with this line: dsi_win=(JAWT_Win32DrawingSurfaceInfo*)dsi->platformInfo;

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