Fix bindings for PixelRef (#1149)

This PR fixes https://youtrack.jetbrains.com/issue/SKIKO-996

The PixelRef bindings have two mistakes in them:

1. `rowBytes` is defined as a `NativePointer`, whereas it is actually an
integer with the number of bytes per row. This is the same as
`Bitmap::rowBytes`.
2. It is missing the `pixels` property that actually returns a pointer
to the pixel data.

See: https://api.skia.org/classSkPixelRef.html

Author: dsvdmeer

skiko/src/commonMain/kotlin/org/jetbrains/skia/PixelRef.kt

@@ -27,13 +27,20 @@ class PixelRef internal constructor(ptr: NativePointer) : RefCnt(ptr) {
         } finally {
             reachabilityBarrier(this)
         }
-    val rowBytes: NativePointer
+    val rowBytes: Int
         get() = try {
             Stats.onNativeCall()
             PixelRef_nGetRowBytes(_ptr)
         } finally {
             reachabilityBarrier(this)
         }
+    val pixels: NativePointer
+        get() = try {
+            Stats.onNativeCall()
+            PixelRef_nGetPixels(_ptr)
+        } finally {
+            reachabilityBarrier(this)
+        }
 
     /**
      * Returns a non-zero, unique value corresponding to the pixels in this
@@ -83,8 +90,11 @@ class PixelRef internal constructor(ptr: NativePointer) : RefCnt(ptr) {
     }
 }
 
+@ExternalSymbolName("org_jetbrains_skia_PixelRef__1nGetPixels")
+private external fun PixelRef_nGetPixels(ptr: NativePointer): NativePointer
+
 @ExternalSymbolName("org_jetbrains_skia_PixelRef__1nGetRowBytes")
-private external fun PixelRef_nGetRowBytes(ptr: NativePointer): NativePointer
+private external fun PixelRef_nGetRowBytes(ptr: NativePointer): Int
 
 @ExternalSymbolName("org_jetbrains_skia_PixelRef__1nGetGenerationId")
 private external fun PixelRef_nGetGenerationId(ptr: NativePointer): Int

skiko/src/commonTest/kotlin/org/jetbrains/skia/PixelRefTest.kt

@@ -0,0 +1,23 @@
+package org.jetbrains.skia
+
+import org.jetbrains.skia.util.assertIsNotNullPointer
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNotNull
+
+class PixelRefTest {
+
+    @Test
+    fun pixelRefTest() {
+        val bitmap = Bitmap()
+        bitmap.allocPixels(ImageInfo.makeS32(7, 3, ColorAlphaType.OPAQUE))
+
+        val pixelRef = bitmap.pixelRef
+        assertNotNull(pixelRef)
+        assertEquals(7, pixelRef.width)
+        assertEquals(3, pixelRef.height)
+        assertEquals(7 * 4, pixelRef.rowBytes)
+        assertIsNotNullPointer(pixelRef.pixels)
+    }
+
+}

skiko/src/commonTest/kotlin/org/jetbrains/skia/util/assertNativePointers.kt

@@ -0,0 +1,13 @@
+package org.jetbrains.skia.util
+
+import org.jetbrains.skia.impl.NativePointer
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+internal expect val NativePointer.isNullPointer: Boolean
+
+fun assertIsNullPointer(ptr: NativePointer) =
+    assertTrue(ptr.isNullPointer, message = "Expected a null pointer")
+
+fun assertIsNotNullPointer(ptr: NativePointer) =
+    assertFalse(ptr.isNullPointer, message = "Expected a non-null pointer")

skiko/src/jvmMain/cpp/common/PixelRef.cc

@@ -14,7 +14,13 @@ extern "C" JNIEXPORT jint JNICALL Java_org_jetbrains_skia_PixelRefKt__1nGetHeigh
     return instance->height();
 }
 
-extern "C" JNIEXPORT jlong JNICALL Java_org_jetbrains_skia_PixelRefKt_PixelRef_1nGetRowBytes
+extern "C" JNIEXPORT jlong JNICALL Java_org_jetbrains_skia_PixelRefKt_PixelRef_1nGetPixels
+  (JNIEnv* env, jclass jclass, jlong ptr) {
+    SkPixelRef* instance = reinterpret_cast<SkPixelRef*>(static_cast<uintptr_t>(ptr));
+    return reinterpret_cast<jlong>(instance->pixels());
+}
+
+extern "C" JNIEXPORT jint JNICALL Java_org_jetbrains_skia_PixelRefKt_PixelRef_1nGetRowBytes
   (JNIEnv* env, jclass jclass, jlong ptr) {
     SkPixelRef* instance = reinterpret_cast<SkPixelRef*>(static_cast<uintptr_t>(ptr));
     return instance->rowBytes();

skiko/src/jvmTest/kotlin/org/jetbrains/skia/util/assertNativePointers.jvm.kt.kt

@@ -0,0 +1,6 @@
+package org.jetbrains.skia.util
+
+import org.jetbrains.skia.impl.NativePointer
+
+internal actual val NativePointer.isNullPointer: Boolean
+    get() = this == 0L

skiko/src/nativeJsMain/cpp/PixelRef.cc

@@ -13,6 +13,12 @@ SKIKO_EXPORT KInt org_jetbrains_skia_PixelRef__1nGetHeight
     return instance->height();
 }
 
+SKIKO_EXPORT KNativePointer org_jetbrains_skia_PixelRef__1nGetPixels
+  (KNativePointer ptr) {
+    SkPixelRef* instance = reinterpret_cast<SkPixelRef*>((ptr));
+    return instance->pixels();
+}
+
 SKIKO_EXPORT KInt org_jetbrains_skia_PixelRef__1nGetRowBytes
   (KNativePointer ptr) {
     SkPixelRef* instance = reinterpret_cast<SkPixelRef*>((ptr));

skiko/src/nativeTest/kotlin/org/jetbrains/skia/util/assertNativePointers.native.kt

@@ -0,0 +1,8 @@
+package org.jetbrains.skia.util
+
+import kotlinx.cinterop.ExperimentalForeignApi
+import org.jetbrains.skia.impl.NativePointer
+
+@OptIn(ExperimentalForeignApi::class)
+internal actual val NativePointer.isNullPointer: Boolean
+    get() = this == NativePointer.NULL

skiko/src/webTest/kotlin/org/jetbrains/skia/util/assertNativePointers.js.kt

@@ -0,0 +1,6 @@
+package org.jetbrains.skia.util
+
+import org.jetbrains.skia.impl.NativePointer
+
+internal actual val NativePointer.isNullPointer: Boolean
+    get() = this == 0