Add LineHeightSpan, RelativeLineHeightSpan and LetterSpacingSpan. Add few examples to example app.

Author: arthufimtcev

app/build.gradle

@@ -4,7 +4,7 @@ android {
 	compileSdkVersion 26
 	defaultConfig {
 		applicationId "io.supernova.supernovauitoolkit"
-		minSdkVersion 16
+		minSdkVersion 21
 		targetSdkVersion 26
 		versionCode 1
 		versionName "1.0"

app/src/androidTest/java/io/supernova/supernovauitoolkit/ExampleInstrumentedTest.java

@@ -1,19 +1,22 @@
 package io.supernova.toolkit.example;
 
-import android.support.v7.app.AppCompatActivity;
 import android.os.Bundle;
+import android.support.v7.app.AppCompatActivity;
 import android.text.SpannableString;
 import android.text.Spanned;
-import android.text.style.LineHeightSpan;
 import android.widget.TextView;
 
 import io.supernova.supernovauitoolkit.R;
-import io.supernova.uitoolkit.text.LineSpacingSpan;
+import io.supernova.uitoolkit.text.LetterSpacingSpan;
+import io.supernova.uitoolkit.text.LineHeightSpan;
+import io.supernova.uitoolkit.text.RelativeLineHeightSpan;
 
 
 public class MainActivity extends AppCompatActivity {
 
 	private TextView exampleTextView;
+	private TextView exampleTextView2;
+
 
 	@Override
 	protected void onCreate(Bundle savedInstanceState) {
@@ -26,11 +29,41 @@ protected void onCreate(Bundle savedInstanceState) {
 
 	private void init() {
 		this.exampleTextView = findViewById(R.id.exampleTextView);
+		this.exampleTextView2 = findViewById(R.id.exampleTextView2);
 
-		SpannableString spannableString = new SpannableString("Example String\nShowcasing line spacing span\nIt's great, trust me");
+		this.setupLineSpacingExample();
+		this.setupLetterSpacingExample();
+	}
 
-		LineHeightSpan lineHeightSpan = new LineSpacingSpan();
+	private void setupLineSpacingExample() {
+
+		SpannableString spannableString = new SpannableString("Example String\nShowcasing line spacing span\nIt's awesome, trust me");
+
+		// Setup line height span
+		LineHeightSpan lineHeightSpan = new LineHeightSpan(40);
 		spannableString.setSpan(lineHeightSpan, 15, 42, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
+
+		// Setup relative line height span
+		RelativeLineHeightSpan relativeLineHeightSpan = new RelativeLineHeightSpan(0.7f);
+		spannableString.setSpan(relativeLineHeightSpan, 44, spannableString.length() - 1, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
+
+		// Pass spannable text to the view
 		this.exampleTextView.setText(spannableString);
 	}
+
+	private void setupLetterSpacingExample() {
+
+		SpannableString spannableString = new SpannableString("Example String\nShowcasing letter spacing span\nIt's awesome, trust me");
+
+		// Setup stretch line height span
+		LetterSpacingSpan stretchingSpan = new LetterSpacingSpan(0.2f);
+		spannableString.setSpan(stretchingSpan, 0, 24, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
+
+		// Setup shrink letter spacing span
+		LetterSpacingSpan shrinkingSpan = new LetterSpacingSpan(-0.1f);
+		spannableString.setSpan(shrinkingSpan, 30, spannableString.length() - 1, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
+
+		// Pass spannable text to the view
+		this.exampleTextView2.setText(spannableString);
+	}
 }

app/src/main/java/io/supernova/toolkit/example/MainActivity.java

@@ -9,19 +9,35 @@
 
 
 	<TextView
-		android:id="@+id/exampleTextView"
+		android:id="@+id/exampleTextView2"
 		android:layout_width="wrap_content"
 		android:layout_height="wrap_content"
-		android:layout_marginBottom="8dp"
 		android:layout_marginEnd="8dp"
 		android:layout_marginLeft="8dp"
 		android:layout_marginRight="8dp"
 		android:layout_marginStart="8dp"
-		android:layout_marginTop="8dp"
 		android:gravity="center"
-		android:text="TextView"
+		android:textSize="14sp"
 		app:layout_constraintBottom_toBottomOf="parent"
 		app:layout_constraintEnd_toEndOf="parent"
 		app:layout_constraintStart_toStartOf="parent"
-		app:layout_constraintTop_toTopOf="parent"/>
+		app:layout_constraintTop_toBottomOf="@+id/exampleTextView"
+		tools:text="TextView"/>
+
+
+	<TextView
+		android:id="@+id/exampleTextView"
+		android:layout_width="wrap_content"
+		android:layout_height="wrap_content"
+		android:layout_marginEnd="8dp"
+		android:layout_marginLeft="8dp"
+		android:layout_marginRight="8dp"
+		android:layout_marginStart="8dp"
+		android:gravity="center"
+		app:layout_constraintBottom_toTopOf="@+id/exampleTextView2"
+		app:layout_constraintEnd_toEndOf="parent"
+		app:layout_constraintStart_toStartOf="parent"
+		app:layout_constraintTop_toTopOf="parent"
+		app:layout_constraintVertical_chainStyle="spread"
+		tools:text="TextView"/>
 </android.support.constraint.ConstraintLayout>

app/src/main/res/layout/activity_main.xml

@@ -0,0 +1,31 @@
+package io.supernova.uitoolkit.text;
+
+import android.os.Build;
+import android.support.annotation.RequiresApi;
+import android.text.TextPaint;
+import android.text.style.MetricAffectingSpan;
+
+
+@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
+public class LetterSpacingSpan extends MetricAffectingSpan {
+
+	private float letterSpacing;
+
+
+	public LetterSpacingSpan(float letterSpacing) {
+		this.letterSpacing = letterSpacing;
+	}
+
+
+
+	@Override
+	public void updateMeasureState(TextPaint p) {
+		p.setLetterSpacing(this.letterSpacing);
+	}
+
+
+	@Override
+	public void updateDrawState(TextPaint tp) {
+		tp.setLetterSpacing(this.letterSpacing);
+	}
+}

app/src/test/java/io/supernova/supernovauitoolkit/ExampleUnitTest.java

@@ -0,0 +1,40 @@
+package io.supernova.uitoolkit.text;
+
+import android.graphics.Paint;
+import android.support.annotation.Nullable;
+import android.text.TextPaint;
+
+
+public class LineHeightSpan implements android.text.style.LineHeightSpan.WithDensity {
+
+	private final int height;
+
+
+	public LineHeightSpan(int height) {
+		this.height = height;
+	}
+
+
+	@Override
+	public void chooseHeight(CharSequence text, int start, int end, int spanstartv, int v, Paint.FontMetricsInt fm) {
+		// Should not get called, at least not by StaticLayout.
+		this.chooseHeight(text, start, end, spanstartv, v, fm, null);
+	}
+
+	@Override
+	public void chooseHeight(CharSequence text, int start, int end, int spanstartv, int v, Paint.FontMetricsInt fm, @Nullable TextPaint paint) {
+		int size = height;
+
+		// Apply density if provided.
+		if (paint != null) {
+			size *= paint.density;
+		}
+
+		this.applyLineHeight(size, fm);
+	}
+
+	private void applyLineHeight(int newHeight, Paint.FontMetricsInt fm) {
+		fm.top = fm.bottom - newHeight;
+		fm.ascent = fm.descent - newHeight;
+	}
+}

lib/src/main/java/io/supernova/uitoolkit/text/LetterSpacingSpan.java

@@ -0,0 +1,44 @@
+package io.supernova.uitoolkit.text;
+
+import android.graphics.Paint;
+import android.support.annotation.Nullable;
+import android.text.TextPaint;
+import android.text.style.LineHeightSpan;
+
+
+public class RelativeLineHeightSpan implements LineHeightSpan.WithDensity {
+
+	private final float lineHeightMultiplier;
+
+
+	public RelativeLineHeightSpan(float lineHeightMultiplier) {
+		this.lineHeightMultiplier = lineHeightMultiplier;
+	}
+
+
+	@Override
+	public void chooseHeight(CharSequence text, int start, int end, int spanstartv, int v, Paint.FontMetricsInt fm) {
+		// Should not get called, at least not by StaticLayout.
+		this.chooseHeight(text, start, end, spanstartv, v, fm, null);
+	}
+
+	@Override
+	public void chooseHeight(CharSequence text, int start, int end, int spanstartv, int v, Paint.FontMetricsInt fm, @Nullable TextPaint paint) {
+
+		// Calculate new line height.
+		float currentHeight = this.getLineHeightFromMetrics(fm);
+		float newHeight = currentHeight * lineHeightMultiplier;
+
+		this.applyLineHeight(((int) newHeight), fm);
+	}
+
+
+	private int getLineHeightFromMetrics(Paint.FontMetricsInt fm) {
+		return fm.descent - fm.ascent;
+	}
+
+	private void applyLineHeight(int newHeight, Paint.FontMetricsInt fm) {
+		fm.top = fm.bottom - newHeight;
+		fm.ascent = fm.descent - newHeight;
+	}
+}