adding code to get windows dpi

build/windows/fenster/Fenster.java

@@ -0,0 +1,33 @@
+package processing.core.platform;
+
+public class Fenster {
+  static void load() {
+    System.out.println("about to load");
+    System.loadLibrary("fenster");
+    System.out.println("loaded");
+  }
+
+  static void info() {
+    System.out.println("about to init");
+    Fenster f = new Fenster();
+    // f.sayHello();
+    System.out.println("about to call");
+    int ppi = f.getLogPixels();
+    System.out.println("getLogPixels = " + ppi);
+    System.out.println("aka " + (ppi / 96f));
+    System.out.println("done");
+  }
+
+  public static void main(String[] args) {
+    new Thread(() -> {
+    // java.awt.EventQueue.invokeLater(() -> {
+      load();
+      info();
+    // });
+    }).start();
+  }
+
+  private native void sayHello();
+
+  private native int getLogPixels();
+}

build/windows/fenster/Makefile

@@ -0,0 +1,26 @@
+JAVA_HOME=/c/Program\ Files/Eclipse\ Adoptium/jdk-17.0.1.12-hotspot
+
+headers:
+	${JAVA_HOME}/bin/javac -h . -d . Fenster.java
+	#rm Fenster.class
+
+default:
+	#ls ${JAVA_HOME}
+	g++ -c \
+		-I${JAVA_HOME}/include \
+	    -I${JAVA_HOME}/include/win32 \
+	    processing_core_platform_Fenster.cpp \
+	    -o processing_core_platform_Fenster.o
+	#-mwindows -lmingw64 -lgdi64 \
+	g++ -shared -o fenster.dll \
+		processing_core_platform_Fenster.o \
+		-lgdi32 \
+        -Wl,--add-stdcall-alias
+
+run:
+	#${JAVA_HOME}/bin/javac -d . Fenster.java
+	${JAVA_HOME}/bin/java -cp . processing.core.platform.Fenster
+# 	java -cp . -Djava\.library\.path=/NATIVE_SHARED_LIB_FOLDER processing.core.platform.Fenster
+
+fest:
+	g++ fester.cpp -o fenster -lgdi32

build/windows/fenster/fenster.cpp

@@ -0,0 +1,26 @@
+#include <stdio.h>
+#include <windows.h>
+
+
+int main() {
+  // MinGW could not find this variant. There's probably a #define or
+  // another arg to make it work, but the Vista-era version is working fine.
+  //SetProcessDpiAwareness(PROCESS_SYSTEM_DPI_AWARE);  // Windows 8.1 and later
+
+  // https://docs.microsoft.com/en-us/windows/win32/hidpi/setting-the-default-dpi-awareness-for-a-process
+  SetProcessDPIAware();  // Windows Vista and later
+
+  // https://docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/dpi-related-apis-and-registry-settings
+  // also done in the JDK https://hg.openjdk.java.net/jdk/jdk/rev/b7a958df3992
+  HDC hdc = GetDC(NULL);
+  if (hdc) {
+    INT horizontalDPI = GetDeviceCaps(hdc, LOGPIXELSX);
+    INT verticalDPI = GetDeviceCaps(hdc, LOGPIXELSY);
+    //printf("%d %d", horizontalDPI, verticalDPI);
+    // god help us if horizontal != vertical
+    printf("%d", horizontalDPI);
+    ReleaseDC(NULL, hdc);
+    return 0;
+  }
+  return 1;
+}

build/windows/fenster/processing_core_platform_Fenster.cpp

@@ -0,0 +1,32 @@
+#include "processing_core_platform_Fenster.h"
+
+// only for the std::cout debugging stuff / remove later
+//#include <ostream>
+//#include <iostream>
+
+#include <windows.h>
+
+// had to manually modify JDK_HOME/include/win32/jni_md.h to change
+// typedef __int64 jlong -> __int64_t
+// was also necessary to modify the permissions of the file in Windows
+
+
+JNIEXPORT void JNICALL Java_processing_core_platform_Fenster_sayHello
+  (JNIEnv *, jobject) {
+    //std::cout << "Well at least this part is working" << std::endl;
+  }
+
+JNIEXPORT jint JNICALL Java_processing_core_platform_Fenster_getLogPixels
+  (JNIEnv *, jobject) {
+    // https://docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/dpi-related-apis-and-registry-settings
+    // also done in the JDK https://hg.openjdk.java.net/jdk/jdk/rev/b7a958df3992
+    HDC hdc = GetDC(NULL);
+    if (hdc) {
+      INT horizontalDPI = GetDeviceCaps(hdc, LOGPIXELSX);
+      ReleaseDC(NULL, hdc);
+      // INT verticalDPI = GetDeviceCaps(desktopDc, LOGPIXELSY);
+      // god help us if horizontal != vertical
+      return (jint) horizontalDPI;
+    }
+    return 0;
+  }

build/windows/fenster/processing_core_platform_Fenster.h

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+/* DO NOT EDIT THIS FILE - it is machine generated */
+#include <jni.h>
+/* Header for class processing_core_platform_Fenster */
+
+#ifndef _Included_processing_core_platform_Fenster
+#define _Included_processing_core_platform_Fenster
+#ifdef __cplusplus
+extern "C" {
+#endif
+/*
+ * Class:     processing_core_platform_Fenster
+ * Method:    sayHello
+ * Signature: ()V
+ */
+JNIEXPORT void JNICALL Java_processing_core_platform_Fenster_sayHello
+  (JNIEnv *, jobject);
+
+/*
+ * Class:     processing_core_platform_Fenster
+ * Method:    getLogPixels
+ * Signature: ()I
+ */
+JNIEXPORT jint JNICALL Java_processing_core_platform_Fenster_getLogPixels
+  (JNIEnv *, jobject);
+
+#ifdef __cplusplus
+}
+#endif
+#endif