Add SDL_GetDisplayDPI implementation on Android. (thanks Rachel!)

android-project/app/src/main/java/org/libsdl/app/SDLActivity.java

@@ -18,6 +18,7 @@ import android.widget.Button;
 import android.widget.LinearLayout;
 import android.widget.TextView;
 import android.os.*;
+import android.util.DisplayMetrics;
 import android.util.Log;
 import android.util.SparseArray;
 import android.graphics.*;
@@ -613,6 +614,10 @@ public class SDLActivity extends Activity {
         return SDL.getContext();
     }
 
+    public static DisplayMetrics getDisplayDPI() {
+        return getContext().getResources().getDisplayMetrics();
+    }
+
     /**
      * This method is called by SDL using JNI.
      */

src/core/android/SDL_android.c

@@ -214,6 +214,7 @@ static jmethodID midClipboardGetText;
 static jmethodID midClipboardHasText;
 static jmethodID midOpenAPKExpansionInputStream;
 static jmethodID midGetManifestEnvironmentVariable;
+static jmethodID midGetDisplayDPI;
 
 /* audio manager */
 static jclass mAudioManagerClass;
@@ -316,11 +317,13 @@ JNIEXPORT void JNICALL SDL_JAVA_INTERFACE(nativeSetupJNI)(JNIEnv* mEnv, jclass c
     midGetManifestEnvironmentVariable = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                 "getManifestEnvironmentVariable", "(Ljava/lang/String;)Ljava/lang/String;");
 
+    midGetDisplayDPI = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass, "getDisplayDPI", "()Landroid/util/DisplayMetrics;");
+
     if (!midGetNativeSurface ||
        !midSetActivityTitle || !midSetOrientation || !midGetContext || !midInputGetInputDeviceIds ||
        !midSendMessage || !midShowTextInput || !midIsScreenKeyboardShown || 
        !midClipboardSetText || !midClipboardGetText || !midClipboardHasText ||
-       !midOpenAPKExpansionInputStream || !midGetManifestEnvironmentVariable) {
+       !midOpenAPKExpansionInputStream || !midGetManifestEnvironmentVariable || !midGetDisplayDPI) {
         __android_log_print(ANDROID_LOG_WARN, "SDL", "Missing some Java callbacks, do you have the latest version of SDLActivity.java?");
     }
 
@@ -1047,6 +1050,28 @@ int Android_JNI_OpenAudioDevice(int iscapture, int sampleRate, int is16Bit, int
     return audioBufferFrames;
 }
 
+int Android_JNI_GetDisplayDPI(float *ddpi, float *xdpi, float *ydpi)
+{
+    JNIEnv *env = Android_JNI_GetEnv();
+
+    jobject jDisplayObj = (*env)->CallStaticObjectMethod(env, mActivityClass, midGetDisplayDPI);
+    jclass jDisplayClass = (*env)->GetObjectClass(env, jDisplayObj);
+
+    jfieldID fidXdpi = (*env)->GetFieldID(env, jDisplayClass, "xdpi", "F");
+    jfieldID fidYdpi = (*env)->GetFieldID(env, jDisplayClass, "ydpi", "F");
+    jfieldID fidDdpi = (*env)->GetFieldID(env, jDisplayClass, "densityDpi", "I");
+
+    float nativeXdpi = (*env)->GetFloatField(env, jDisplayObj, fidXdpi);
+    float nativeYdpi = (*env)->GetFloatField(env, jDisplayObj, fidYdpi);
+    int nativeDdpi = (*env)->GetIntField(env, jDisplayObj, fidDdpi);
+
+    *ddpi = (float)nativeDdpi;
+    *xdpi = nativeXdpi;
+    *ydpi = nativeYdpi;
+
+    return 0;
+}
+
 void * Android_JNI_GetAudioBuffer(void)
 {
     return audioBufferPinned;

src/core/android/SDL_android.h

@@ -42,6 +42,8 @@ extern void Android_JNI_HideTextInput(void);
 extern SDL_bool Android_JNI_IsScreenKeyboardShown(void);
 extern ANativeWindow* Android_JNI_GetNativeWindow(void);
 
+extern int Android_JNI_GetDisplayDPI(float *ddpi, float *xdpi, float *ydpi);
+
 /* Audio support */
 extern int Android_JNI_OpenAudioDevice(int iscapture, int sampleRate, int is16Bit, int channelCount, int desiredBufferFrames);
 extern void* Android_JNI_GetAudioBuffer(void);

src/video/android/SDL_androidvideo.c

@@ -47,6 +47,7 @@
 /* Initialization/Query functions */
 static int Android_VideoInit(_THIS);
 static void Android_VideoQuit(_THIS);
+int Android_GetDisplayDPI(_THIS, SDL_VideoDisplay * display, float * ddpi, float * hdpi, float * vdpi);
 
 #include "../SDL_egl_c.h"
 #define Android_GLES_GetProcAddress SDL_EGL_GetProcAddress
@@ -115,6 +116,8 @@ Android_CreateDevice(int devindex)
     device->VideoQuit = Android_VideoQuit;
     device->PumpEvents = Android_PumpEvents;
 
+    device->GetDisplayDPI = Android_GetDisplayDPI;
+
     device->CreateSDLWindow = Android_CreateWindow;
     device->SetWindowTitle = Android_SetWindowTitle;
     device->DestroyWindow = Android_DestroyWindow;
@@ -198,6 +201,12 @@ Android_VideoQuit(_THIS)
     Android_QuitTouch();
 }
 
+int
+Android_GetDisplayDPI(_THIS, SDL_VideoDisplay * display, float * ddpi, float * hdpi, float * vdpi)
+{
+    return Android_JNI_GetDisplayDPI(ddpi, hdpi, vdpi);
+}
+
 void
 Android_SetScreenResolution(int width, int height, Uint32 format, float rate)
 {