Fix linux dpi (#128)

* Fix dpi scaling issue on Linux.

samples/SkijaInjectSample/build.gradle.kts

@@ -52,6 +52,7 @@ val additionalArguments = mutableMapOf<String, String>()
 
 val casualRun = tasks.named<JavaExec>("run") {
     systemProperty("skiko.fps.enabled", "true")
+    systemProperty("skiko.linux.autodpi", "true")
     systemProperty("skiko.hardwareInfo.enabled", "true")
     jvmArgs?.add("-ea")
     // Use systemProperty("skiko.library.path", "/tmp") to test loader.

skiko/src/jvmMain/cpp/linux/drawlayer.cc

@@ -55,6 +55,17 @@ extern "C"
         return 1;
     }
 
+    double getDpiScale() {
+        Display *display = XOpenDisplay(nullptr);
+        if (display != nullptr) {
+            double result = getDpiScaleByDisplay(display);
+            XCloseDisplay(display);
+            return result;
+        } else {
+            return 1;
+        }
+    }
+
     JNIEXPORT jfloat JNICALL Java_org_jetbrains_skiko_PlatformOperationsKt_linuxGetDpiScaleNative(JNIEnv *env, jobject properties, jlong platformInfoPtr)
     {
         JAWT_X11DrawingSurfaceInfo *dsi_x11 = fromJavaPointer<JAWT_X11DrawingSurfaceInfo *>(platformInfoPtr);
@@ -67,4 +78,10 @@ extern "C"
        return 2;
     }
 
+
+    JNIEXPORT jfloat JNICALL Java_org_jetbrains_skiko_SetupKt_linuxGetSystemDpiScale(JNIEnv *env, jobject layer)
+    {
+        return (float) getDpiScale();
+    }
+
 } // extern "C"
\ No newline at end of file

skiko/src/jvmMain/kotlin/org/jetbrains/skiko/Library.kt

@@ -79,11 +79,7 @@ object Library {
         }
 
         // TODO move properties to SkikoProperties
-        Setup.init(
-            System.getProperty("skiko.rendering.noerasebackground") != "false",
-            System.getProperty("skiko.rendering.laf.global") == "true",
-            System.getProperty("skiko.rendering.useScreenMenuBar") != "false"
-        )
+        Setup.init()
 
         try {
             // Init code executed after library was loaded.

skiko/src/jvmMain/kotlin/org/jetbrains/skiko/PlatformOperations.kt

@@ -110,18 +110,6 @@ internal val platformOperations: PlatformOperations by lazy {
 
                 override fun getDpiScale(component: Component): Float {
                     return component.graphicsConfiguration.defaultTransform.scaleX.toFloat()
-                    // TODO doesn't work well because java doesn't scale windows (content has offset with 200% scale)
-                    //
-                    // Two solutions:
-                    // 1. dynamically change sun.java2d.uiScale (it is global property,
-                    // so we have to be careful) and update all windows
-                    //
-                    // 2. apply contentScale manually to all windows
-                    // (it is not good, because on different platform windows will have different size.
-                    // Maybe we will apply contentScale manually on all platforms?)
-
-                    // see also comment for HardwareLayer.checkContentScale
-                    // return component.useDrawingSurfacePlatformInfo(::linuxGetDpiScaleNative)
                 }
 
                 override fun createRedrawer(

skiko/src/jvmMain/kotlin/org/jetbrains/skiko/Setup.kt

@@ -4,10 +4,16 @@ import javax.swing.UIManager
 
 object Setup {
     fun init(
-        noEraseBackground: Boolean = true,
-        globalLAF: Boolean = false,
-        useScreenMenuBar: Boolean = true
+        noEraseBackground: Boolean = System.getProperty("skiko.rendering.noerasebackground") != "false",
+        globalLAF: Boolean = System.getProperty("skiko.rendering.laf.global") == "true",
+        useScreenMenuBar: Boolean = System.getProperty("skiko.rendering.useScreenMenuBar") != "false",
+        autoLinuxDpi: Boolean = System.getProperty("skiko.linux.autodpi") == "true"
     ) {
+        if (hostOs == OS.Linux && autoLinuxDpi) {
+            val scale = linuxGetSystemDpiScale()
+            System.setProperty("sun.java2d.uiScale.enabled", "true")
+            System.setProperty("sun.java2d.uiScale", "$scale")
+        }
         if (noEraseBackground) {
             // we have to set this property to avoid render flickering.
             System.setProperty("sun.awt.noerasebackground", "true")
@@ -25,3 +31,5 @@ object Setup {
         }
     }
 }
+
+private external fun linuxGetSystemDpiScale(): Float