Need Help with a Skiko Issue (Incorrect Text Width) _Wasm/Js and Native Environments_ In the Skiko p...

# multiplatform

[Saivignesh S]

Need Help with a Skiko Issue (Incorrect Text Width) Wasm/Js and Native Environments
In the Skiko project, I’ve encountered a potential issue with text measurement and encoding. Here's the context:
• In Skiko Native.native.kt, Native.js.kt, and Native.wasm.kt, there is an actual implementation of the expect function toInterOp declared in Native.kt (CommonMain).
• The function uses convertToZeroTerminatedString() to convert a String to a ByteArray, encoding it to UTF-8.
However, in NativeJsMain/Cpp/Font.cc, the measureText function is configured as follows:

SKIKO_EXPORT KFloat org_jetbrains_skia_Font__1nMeasureTextWidth
  (KNativePointer ptr, char* str, KInt len, KNativePointer paintPtr) {
    SkFont* instance = reinterpret_cast<SkFont*>(ptr);
    SkPaint* paint = reinterpret_cast<SkPaint*>(paintPtr);
    return instance->measureText(str, len * sizeof(KChar), SkTextEncoding::kUTF16, nullptr, paint);
}

The problem: measureText expects a UTF-16 encoded string, but the input string is in UTF-8

Below Snippet is from jvmMain/cpp/Font.cc ,In this case, Text Measuring returns the correct width ( JVM Environment ), where the String's are processed as UTF-16.

extern "C" JNIEXPORT jfloat JNICALL Java_org_jetbrains_skia_FontKt__1nMeasureTextWidth
  (JNIEnv* env, jclass jclass, jlong ptr, jstring str, jint len, jlong paintPtr) {
    SkFont* instance = reinterpret_cast<SkFont*>(static_cast<uintptr_t>(ptr));
    SkPaint* paint = reinterpret_cast<SkPaint*>(static_cast<uintptr_t>(paintPtr));
    const jchar* chars = env->GetStringCritical(str, nullptr);
    jfloat result = instance->measureText(chars, len * sizeof(jchar), SkTextEncoding::kUTF16, nullptr, paint);
    env->ReleaseStringCritical(str, chars);
    return result;
}

Workaround:
Changing the encoding to UTF-8 in the measureText function gives the correct text width:

SKIKO_EXPORT KFloat org_jetbrains_skia_Font__1nMeasureTextWidth
  (KNativePointer ptr, char* str, KInt len, KNativePointer paintPtr) {
    SkFont* instance = reinterpret_cast<SkFont*>(ptr);
    SkPaint* paint = reinterpret_cast<SkPaint*>(paintPtr);
    return instance->measureText(str, len, SkTextEncoding::kUTF8, nullptr, paint);
}

Question:
Is this workaround correct, or am I addressing the issue incorrectly? If there’s a better way to ensure proper font measurement, I’d appreciate any guidance.
Thanks in advance for your help!

[Artem Kobzar]

@Oleksandr Karpovich [JB] ^^

[Oleksandr Karpovich [JB]]

I believe your workaround is rather correct.
Initially there were only the bindings for java. Then when the bindings were added for k/native and k/web, some code was migrated from the existing bindings. And probably it's a mistake of the copy/paste.

I see you've already reported this problem https://youtrack.jetbrains.com/issue/SKIKO-995/Skiko-Text-Measurement-Encoding-Issue-Font.measureTextWidth

Thank you 🙂

[Oleksandr Karpovich [JB]]

Do you use these methods directly?
I believe we missed the problem, because in Compose it's using Paragraph, which can return lineMetrics.

[Saivignesh S]

Yes, I'm using Font.measureTextWidth() directly in my code. I also tried using ParagraphBuilder, add text and retrieve the bounds, and it does return the correct text width. However, I needed a more straightforward approach, which is why I relied on Font.measureTextWidth().
Thanks again 😀

[Saivignesh S]

Hi @Oleksandr Karpovich [JB]
Any update 🙂

Thanks in advance.

[Oleksandr Karpovich [JB]]

Hey! No updates yet. Would you like to create a pull request + the tests?