Premultiply Alpha in BufferedImageTextureHolder

Initialize texture with premultiplied alpha, as expected by shader.

jvm/src/main/java/io/openmobilemaps/mapscore/graphics/BufferedImageTextureHolder.java

@@ -3,6 +3,8 @@
 import io.openmobilemaps.mapscore.graphics.util.GlTextureHelper;
 import io.openmobilemaps.mapscore.shared.graphics.objects.TextureHolderInterface;
 
+import org.jetbrains.annotations.NotNull;
+
 import java.awt.image.BufferedImage;
 
 /** Implementation of the TextureHolderInterface for BufferedImage and OpenGL. */
@@ -11,7 +13,18 @@ public class BufferedImageTextureHolder extends TextureHolderInterface {
     protected int usageCounter;
     protected int textureId;
 
-    public BufferedImageTextureHolder(BufferedImage image) {
+    /**
+     * Construct a BufferedImageTextureHolder.
+     *
+     * <p>NOTE: this may modify the image by calling {@link BufferedImage#coerceData} to ensure that
+     * we have premultiplied alpha image data.
+     *
+     * @param image Image, may be modified during the constructor
+     */
+    public BufferedImageTextureHolder(@NotNull BufferedImage image) {
+        // premultiply alpha
+        image.coerceData(true);
+
         this.image = image;
         this.usageCounter = 0;
     }